Aircon gurus -- check in

Reprise

Lifetime VIP Supporter
Hell, I'll even take semi-gurus. :laugh:


Background:

3 vehicles
0 with working A/C
1 (Sierra) had all seals replaced during my build, and the correct amt / type of PAG oil added
(new receiver/drier, and drained oil out of compressor & added new, per specs. Also drained / re-oiled condenser)

2 hold vacuum fine, per the manifold gauge set (only about 22lbs @ ~ 700ft elevation, but both are same, & stable)
Temps warming up & gonna be upper 80s - 90s F in a few days

Watched Eric the Car Guy videos a few times about recharging A/C
If there's one thing I'm good at, it's following directions, if they're halfway decent :book:
Heeding advice elsewhere NOT to overfill (a little difficult with partial 12oz cans; I'm acknowledging neither vehicle has a full charge.
However, in the past, when I've used those 'hack' A/C 'recharge in a can' (per Eric), I've noted compressor clutch starts cycling very quickly.

Vehicle I'm talking mainly about -- '03 Sierra Crew Cab (with auto climate)
Closed off both high / low sides
Hooked up 12oz can of R134a
Started truck & set A/C & fan on high
Opened up the can and the low side (blue) and let it start filling

Refrigerant loosened up the low side connector hose at the valve, and lost a little refrigerant in the process (and maybe introduced air?) Tightened up and rechecked all connections -- no more issues.

Capacity for the Sierra, per GM service manual, is 1.6 lb (25.6 oz). @ 11oz realized per 12oz can, that's 2 full and 1 partial can.
1st can in and low / high side gauges roughly equalized at 70 somethings-or-other (using the larger 'black' scales, which represent different things on each gauge). NO cycling
2nd can in, gauges equalized at just above 90 something-or-others. STILL no cycling (!) :wowfaint: Estimate 21-22oz in (again, hard to tell, with cans)
Shut truck down (running in enclosed garage).
Ambient is upper 60s Fahrenheit, not a ton of humidity.
Decided to check in w/ forum for advice / follow-up questions


Other vehicle, for reference (Honda Accord, which uses a Denso compressor, just like the Sierra)
Did this one a couple of weeks ago.
Capacity is about 16-19oz (forgot, but I have the info handy)
Added (1) 12oz can -- no cycling.
Gauges equalized at about 70 something-or-others during process.
Ambient was 50s at the time, but have since turned on when warmer -- no difference (so ambient temp is little / no factor here)
Was going to let dealer look at it (always a mistake) while they were taking care of two open recalls. Need to take it in soon, to stop the near-weekly notifications from Mother Honda.

I very much doubt *both* Denso compressors are trashed.
In the case of the Sierra, when I had the truck apart, I made sure the clutch still spun freely.
The truck didn't have an A/C belt when I bought it, and the one I put on is still intact (so the clutch didn't lock up and rip it off).

Suggestions?
Do I just need to go for the full charge? Like I said... I'd expect *some* cycling, from both, at this point.
 

TJBaker57

Well-Known Member
I am having a hard time following here. Are you saying your high and low pressures are about the same while the compressor is running!!
 

TJBaker57

Well-Known Member
2 hold vacuum fine, per the manifold gauge set (only about 22lbs @ ~ 700ft elevation, but both are same, & stable

Do what now?? Are you speaking of pulling a vacuum on the system with a vacuum pump for evacuation/dehydration of the system prior to adding in the charge? If so you should be seeing something on the order of 29.7 inches of HG vacuum or greater for best results.
 
OP
Reprise

Reprise

Lifetime VIP Supporter
I am having a hard time following here. Are you saying your high and low pressures are about the same while the compressor is running!!
No, in that I only consider the compressor to be running when the clutch is engaged (am I wrong, here?) The pressures eventually roughly equalize with one another on both vehicles (and they're close to one another to begin with), so I figured I'd point that out.

I know that if the compressor engages, I'll see the gauges change. Right now, they're steady.


Do what now?? Are you speaking of pulling a vacuum on the system with a vacuum pump for evacuation/dehydration of the system prior to adding in the charge? If so you should be seeing something on the order of 29.7 inches of HG vacuum or greater for best results.

Yes -- I'm using a (brand new 2.5cfm) vacuum pump, and on each vehicle, the pump is creating about 22 inches, per the gauges.

I know in a 'perfect' world, the number should be closer to 30. But 30 is just about impossible on earth, unless I'm located in a hurricane or similar. The fact that the two dissimilar vehicles pull / maintain about the same vacuum is telling me (at least) that both of them have a pretty leak-free environment, IMO. Or the pump is faulty, but I doubt that. And I'm even using the recommended 'Black Gold' oil in the pump.

In the case of the Honda (which I did first), I left the vacuum connected for the better part of 2 days, for what it's worth. The Sierra only got about 2hrs on / off the pump, but just as stable, vacuum-wise.
 

Mooseman

Moderator
So the compressor isn't running? Have you tried shorting the low pressure switch? Maybe the switch is bad. If it still doesn't run, check the high side switch. There's also the relay and fuse. Beyond that, something is telling the compressor to not run. Hook up your Tech 2 and see what the pressure switches are reporting and the compressor commanded on/off.

It is normal for a non-running compressor to have equal pressures between low and hoigh side. If you have pressure in the system above the low switch cutoff, it should run.
 
OP
Reprise

Reprise

Lifetime VIP Supporter
Thx, Moose. Appreciate the feedback. Will find the A/C settings in the Tech 2 (hate the menuing in that thing...lol) and see what it reports out
 

TJBaker57

Well-Known Member
, in that I only consider the compressor to be running when the clutch is engaged (am I wrong, here?)

You are correct there.



know in a 'perfect' world, the number should be closer to 30. But 30 is just about impossible on earth, unless I'm located in a hurricane or similar.

This is incorrect here. Well sort of. Yes you will not see 30 inches of HG,,, but 29.9something is possible and this is what is actually desired! The big issue is that standard gauges (bourdon tube) simply cannot measure to this level of accuracy. This is why in the professional world of HVAC we use electronic gauges for vacuum here. Like this here... This was my final pull down on my TrailBlazer yesterday....

20210518_084112.jpg



549 microns is roughly the equivalent of 29.89 in Hg.

If indeed you are only getting to 22 in Hg then you are leaving moisture in the system. That alone will not cause it not to work but it can lead to a shortened life of compresaor etc due to formation of acids and such and in some cases can cause intermittent operation due to the formation of ice crystals in the refrigerant. Yes, the drier will help but a deeper vacuum is better as it removes the moisture from the system and that is the bigger goal in evacuating a system. At 22 inches of Hg water vaporises at about 150° fahrenheit. So in your case the moisture just stayed in the system. At my approx 29.89 inches Hg water boils at about 0° F so residual moisture in my A/C circuit vaporised and was removed from the system.

It can take a long time to fully evacuate a system that has been moisture compromised as the pressure (vacuum) must be low enough to cause the moisture to boil off and be removed from the system.

Is this likely causing an issue right now?? Not likely. By now I have forgotten what the issue is/was!! Will post this and re-read :wink:
 

TJBaker57

Well-Known Member
In the case of the Honda (which I did first), I left the vacuum connected for the better part of 2 days, for what it's worth.

This is worth a lot!! If the gauge used to read the vacuum is accurate I suspect a leak or two in the system.
 

TJBaker57

Well-Known Member
using a (brand new 2.5cfm) vacuum pump, and on each vehicle, the pump is creating about 22 inches, per the gauges.


New pumps normally state their max vacuum specs. Have any such info?

Can you post your setup, ie: what gauges, what is connected to what and how etc? Is it possible there is a leak in the gauge set or hose connections? I know I have some very small leaks in my equipment right now or I would have seen even less the the 549 microns I got.


That said I agree with @Mooseman that whatever is causing the compressor not to engage needs attention as that is your primary issue right now.
 

Beacon

Well-Known Member
My 2 cents, on the Honda... Make sure you're getting power to the clutch coil. And as @TJBaker57 advised me in another post, there should be continuity in that coil.
 

NJTB

Silver Supporter
As Mooseman said, jump the low pressure switch on the accumulator. If the A/C clutch engages, it's either a low charge or a bad switch.
If there's no engagement, look at the high pressure switch, it's on the lines near the compressor.
I know what you mean about the menus on the Tech 2. On one, you have most of the A/C info, however, there's another menu that has the rest of it (Powertrain and Body? Don't remember). The good part is you can check all the switches, sensors, etc. from there.
I had an intermittent problem with the high pressure switch that drove me nuts (bad wire) until I hunted around and found the other menu that had the switches output.
 

xavierny25

Well-Known Member
You are correct there.





This is incorrect here. Well sort of. Yes you will not see 30 inches of HG,,, but 29.9something is possible and this is what is actually desired! The big issue is that standard gauges (bourdon tube) simply cannot measure to this level of accuracy. This is why in the professional world of HVAC we use electronic gauges for vacuum here. Like this here... This was my final pull down on my TrailBlazer yesterday....

View attachment 100442



549 microns is roughly the equivalent of 29.89 in Hg.

If indeed you are only getting to 22 in Hg then you are leaving moisture in the system. That alone will not cause it not to work but it can lead to a shortened life of compresaor etc due to formation of acids and such and in some cases can cause intermittent operation due to the formation of ice crystals in the refrigerant. Yes, the drier will help but a deeper vacuum is better as it removes the moisture from the system and that is the bigger goal in evacuating a system. At 22 inches of Hg water vaporises at about 150° fahrenheit. So in your case the moisture just stayed in the system. At my approx 29.89 inches Hg water boils at about 0° F so residual moisture in my A/C circuit vaporised and was removed from the system.

It can take a long time to fully evacuate a system that has been moisture compromised as the pressure (vacuum) must be low enough to cause the moisture to boil off and be removed from the system.

Is this likely causing an issue right now?? Not likely. By now I have forgotten what the issue is/was!! Will post this and re-read :wink:
Off topic:
nice gauge there @TJBaker57 .
I just recently picked 1 of those up for the split system I'm installing at home. Have to do a pressure test first and check all the flare fittings tomorrow morning. By the afternoon I should have the vaccum pulled and ready to run. The condenser comes pre charged (w/410a) for about 150' of line set, I'm short of that by about 20' so I should be good there. Have a fresh 30lbs tank of 410a just in case.
I haven't used my hvac gauges in about 3 yrs. I really should look them over. I'm really into the digital gauges but not trying to invest $400-$600 in a tool I'll only use ones every few yrs.
 

TJBaker57

Well-Known Member
Sometimes I like to begin by confirming the clutch circuit by jumping the A/C relay at the fuseblock. Jumper terminals 87 to 30. The clutch should engage even without the engine running or the key inserted as power to the relay is hot at all times.
 

TJBaker57

Well-Known Member
Have to do a pressure test first and check all the flare fittings tomorrow morning.

Pay particular attention to those flares. They are the most common leak source. Compared to a standard flare the face of a 410a flare is larger and the flare nuts are heavier than standard flares to accomodate the higher torque they require.
 

xavierny25

Well-Known Member
Pay particular attention to those flares. They are the most common leak source. Compared to a standard flare the face of a 410a flare is larger and the flare nuts are heavier than standard flares to accomodate the higher torque they require.
I'm well aware and to be completely honest I was really considering just cutting out all the flares and use an expander at the head units lines and just brazing the lines together. Which I can probably still do if they are an issue. Not so lucky at the condenser though as those can't be cut and brazed. I'm hopeful I did a good job at each flare and that they are torqued correctly. I used to work for and with my X-father-in-law he had small hvac-r company and we used to install these systems all the time with no issues. Of course now that kind of feels like ages ago coming on 11yrs since my divorce.

SORRY @Reprise for jumping in on your thread. Carry on folks.
 

c good

Well-Known Member
I had a compressor on my Envoy with around 130k miles that had too much "air gap" and a weak field coil. System was fully charged, low and high pressure cut outs were good. PCM "calling" compressor. It would run for awhile, and then just shut off as it got hotter outside. Cool weather no problem. It would run perfectly. When it got hot outside, boom...it would just turn off. I installed a new compressor and everything was better. I could not find a field coil separately otherwise I would have tried that. Others have had this problem and just took the clutch off and removed a shim. This allows the clutch plate to be closer to the electromagnet and allows easier and more positive lock up.
 
OP
Reprise

Reprise

Lifetime VIP Supporter
Ok... I'm back. And based on suggestions / findings, I'm pretty sure that (at least) the clutch on the compressor is gone. Since there's about $30 difference between a clutch kit and an entirely new compressor... I'm likely going with (at least one) new compressor.

(@xavierny25 -- No worries at all, and I'm glad you & TJBaker were able to exchange info. But in keeping this thread 'vehicle-related', maybe it would be a good idea to move your posts into their own 'off-topic' thread? Discuss w/ mods, if desired.)


Catching up...

@TJBaker -- your posts were *quite* helpful, and woke me up out of my stupor. :sleeping:

I had said "well, both compressors can't be bad". BUT -- I have *no* history with either vehicle's A/C system (I purchased both with inop A/C). So... from a logic standpoint, how do I *know* they can't both be bad? I can't (without going through the steps of testing them). The Accord is moving down to 3rd in 'priority', as the Envoy had cranking A/C before it lost its charge late last year (gradually got weaker, not a sudden stoppage).

Anyway... back to TJBaker's post / info...
He mentioned that I should be damned close to 29.xx in. of vacuum. He also asked what the specs were on my fancy new pump. Well... it's spec'd at 29.xx in. 'ultimate vacuum'. Or 5Pa (which most people said, "yeah, right", in their Amzn reviews)
Since I can only get 22-ish in. out of it... and the 'negative' reviews indicated 22-25 in. was all they could get... I know now that my new pump is defective, per the mfg's own specs. Unfortunately, it's too late to return it, and while it's technically in-warranty, a couple of people indicated the vendor ghosted when contacted... I'll probably spring for another pump (yes, I can probably get Amazon to step up, if I wanted to pursue it, but I've had it about 8mos now -- I'll spare the details of my ownership experience). It was the highest reviewed of the cheaper pumps, not that 2000 reviews with about 80% positive means anything, on Amazon (it really doesn't... but I digress).

So... likely, a bad pump, which doesn't preclude me from getting / maintaining *some* vacuum, but not *optimal* vacuum, to ensure moisture burnoff. That's the first issue.

Broke out the Tech2, and I did find the menus for the HVAC, without too much trouble. And it did report the 'pressure switch' as 'normal' (it didn't differentiate between high / low). But, using this was an unfulfilling experience, to be kind, as things that I was ostensibly supposed to be able to command (per my logic)... didn't respond, as I thought they would, specifically with the control head (RPO CJ2 -- the automatic system). I didn't bother with the door mode actuators, as I've not been having trouble with them, and didn't want to *create* any.

Again, I'll spare details. But I'm giving some thought to selling the Tech2, and getting a different tool, for the future. I'll be using it on the Envoy, to see if I have the same experience, there (I know it has no issues with the control head).

Next, I tried jumpering the low pressure switch (the harness plug), at the accumulator (or receiver / drier, as I called it yesterday -- same thing). Had the engine running, and could detect no engagement of the clutch. Again, thanks to Moose for his suggestions, as always.

After that, I checked the underhood fuse box / relays. 2 10A fuses (both good), and 1 relay. Interchanged the DRL & low beam relays (which I know are good)... no improvement.

Finally, I ran across TJBaker's suggestion to jumper 87 and 30 on the relay, which should energize the clutch at all times, given the 'constant hot' on 87.
First, I disconnected the belt from the compressor, so that it would have no resistance from turning. The first time I jumpered the two pins on the box, I thought I might (?) have heard a tiny, tiny faint noise in that area? But only once.

Given that, I think the clutch / compressor is buggered on the Sierra, and I'm going to order one up after posting here.

There *is* one more thing I need to check, and that's to remove the 'deslugger' device I have in series between the compressor and its harness (it's a plug/play, with connectors at both ends, so I didn't have to cut any wiring. But it's a potential failure source, so I have to check that, too, and retest everything above. Depending on results, I'll also breakout the DMM and ensure continuity at all of the system points.

After that, I'm going to grab some more R134a, this time for the Envoy (and for what I'll need for the other two, as well), and see if I can get the A/C running on that one (because I know it worked, previously). Wasn't planning on driving it much this summer, but it's the one that I'll have the least guesswork to fix. Looked up the spec, and since I have the rear air -- which I don't use -- I'll need 2.6lb / 42.4 oz. of R134a for that truck, alone. :yikes:

HOPEFULLY, it'll hold vacuum, and I won't have to replace the rear aircon lines (or find a workaround to block them off, if they're leaking. I already have replacement seals, and figured I'd have to replace all of those -- no biggie, there.

My thanks, as always, to everyone who chimed in, even if I didn't mention you by name. And this thread can stay open, in case anyone wants to continue to add info (and I can also post back, once I get the A/C on 1, 2, or all 3 working again)
 

TJBaker57

Well-Known Member
There *is* one more thing I need to check, and that's to remove the 'deslugger' device I have in series between the compressor and its harness

By design this device interferes with the normal operation of the clutch so I would recommend all testing be done with this device removed.
 

TJBaker57

Well-Known Member
Looked up the spec, and since I have the rear air -- which I don't use -- I'll need 2.6lb / 42.4 oz. of R134a

There should be a sticker in the engine compartment that lists R134a capacity of the system. On mine it is on the airbox. This would override any other spec.
 
OP
Reprise

Reprise

Lifetime VIP Supporter
By design this device interferes with the normal operation of the clutch so I would recommend all testing be done with this device removed.
Yes -- and I had forgotten about it, yesterday. I did remove it today, and retested. Same results, though :worried:
There should be a sticker in the engine compartment that lists R134a capacity of the system. On mine it is on the airbox. This would override any other spec.
Yep - I'm familiar with that. But I'm so used to working with the service manuals. That said, I'll look and verify what's on my airbox lid (pretty sure I still have the label)
Here is a brief look at my 2002 A/C clutch activating and releasing as I jump the relay terminals...

Yes - you figured out I was looking for the thing to *spin*, not be drawn back / energized via electromagnetism. :dunce: Thanks for this. I'll recheck, but I know I would've heard that sound, tbh.
 

Mektek

Well-Known Member
I use a recycled compressor from a window AC unit as a vacuum pump. It goes to 28-29".
I have another more powerful vacuum pump but it's only needed for large split systems.
The small compressor works fine for small automotive AC systems and was free!

In the last 2 cars where I replaced compressors I found the orifice tube screen 2/3 blocked. So If you've never checked it it only costs a few dollars to replace.
 
OP
Reprise

Reprise

Lifetime VIP Supporter
That's a great idea with the compressor. I found a Mac Tools-branded Robinaire pump on CL, and the guy says it pulls 29" quickly.
And I have a new orifice tube - it came with the line I replaced during my head / cam swap. So it and the accumulator are new. By Saturday, the only major 'old' component will be the condenser.
 

aaserv

Well-Known Member
All the auto parts around here rent Vacuum pumps. Id probably put fresh oil in one even if the oil looked clean that was in one. I bought a set of gauges strictly for Auto use at Harbor Freight for less than 30 bucks. You definitely cant get a good vacuum if your gauges or hoses or leaking. If your doing charging very often you should probably look into getting a charging cylinder. You put the gas into them and you can see how much your putting into the vehicle.....probably a good many used 1's out there on the market since every refrigeration guy used to have to have 1 but they are not so much needed anymore with all the electronic equipment used today. They come in various sizes but a small 1 used for refrigerators that only holds a couple lbs should be fine for auto work.

If you suspect moisture in the system that is a whole different problem itself. For 1 you cant use too big of a vacuum pump as it will not get the moisture out, the 2.5 or 3 will probably be fine but I would just crack open the gauges and not open them fully for the 1st couple of hours. Its fairly common practice to pull the vacuum down to 25/27 or so and then add enough R-134 to get it above 0 and repeat the entire vacuum process again. Another thing is if your pump wont pull down it could be because of moisture in the system. Ideally I would want to run Dry Nitrogen thru the system 1st if the moisture is causing that big of a problem but thats probably out of the range of most Diy'S.... In my experiance systems rarely have moisture problems unless the moisture was introduced into the system by the mechanic thru improper procedures. I think people worry a lil to much about moisture actually and most shops just like to talk it up as a reason to skyrocket the charges..
 

littleblazer

Gold Supporter
I actually had the AC crap out in the sierra last week. Worked alright when cool out and nothing when warm, as in above 70 degrees. In my mind I already know what that meant... at 310k and in use its entire life the friction material on the clutch wore off... the air gap was fine it's just with the compressor engaged it still spun free because it was just metal on metal trying to compress a gas... long and short, about 120$ in parts and 40$ in tools it was fixed in about 2 hours. This could potentially be your issue... but I am not too sure. For laughs I attached the hammered out pulley.
20210522_021216.jpg
 
OP
Reprise

Reprise

Lifetime VIP Supporter
So for the garden variety DIY auto A/C servicing this may be a bit much,,, but for those with a desire to know more.....
Well, that describes me to a 'T'... so I thank you (and recommend following the link, for the curious amongst us). I also saved the chart to my HDD, for future reference.
If your doing charging very often you should probably look into getting a charging cylinder. You put the gas into them and you can see how much your putting into the vehicle.....
Believe it or not, that's one of the things that most annoys me... it's stressed that 'exactly' the right amount of refrigerant be used (+/- maybe 0.5lb ?) and yet nothing really exists to be able to measure the transferred amount (without spending $$$($) on pro equipment.)
I will definitely look into this. Thanks for the info.
long and short, about 120$ in parts and 40$ in tools it was fixed in about 2 hours.
Kudos to you (seriously, not sarcastic-like). For me, I compare $160 and 2hrs (if I'm lucky) to $185 and the same 2hrs for a completely new assembly... and I kinda go for the latter. That's what I found as well, when I was looking at clutch vs. new unit.

Seems to me that the price delta between clutch & complete unit didn't used to be so great (my age is showing here, I guess... but it really wasn't that long ago). Anyone else waiting to see if rescinded tariffs actually lower prices back down on goods from PRC? I'm guessing 'not' (and I don't want to get too off-track / political). Just my musings.


So... my latest...
Took the Sierra back outside, while I wait for it's new compressor (later today), and pulled the Envoy in. Yes... same 21-22" of vacuum. And as I suspected, it didn't hold -- in 30min, it lost all pressure. That's fine, I have seals, right?
As I got ready to replace them, the light bulb went on, and I realized that *this* was the right time to get a rear blockoff kit, even if that wasn't the source of the leak. Searched Google for the kit / info, and where was the best info? Right here, on GMTN, thanks to Mooseman's post from about a year ago. Ordered up a kit from the Bay, and it'll be here in a few days. Which now makes the Sierra the 'winner' in, 'which vehicle can deliver cool, refreshing A/C to me first?'

(For a couple of reasons) I felt like Thanos, in Avengers: Endgame... "You could not live with your own failure. Where did that bring you? Back to me." :hahano:
(as an aside... for some odd reason, I think that's one of the great movie lines of the last 20yrs or so)

So now I'm on hold again for a bit, until I get the new (to me) vacuum pump tomorrow from a guy on CL... a MAC-branded Robinaire, for $65. It's about 90min away, so I arranged a pickup time in the morning, before it gets too hot outside... LOL. And he'll demo how fast it pulls down to +29.xx in., before I hand over the cash. He advertised it as 'quick'. We'll see. I looked for a long time on CL, months ago, before giving up and buying the POS I got from Amazon. Wish this had been available, then. Oh, well...

(Yes, I could rent a pump, and save a few hours (and have a vehicle with working A/C to go pick the CL one up (I knew someone would bring that up)... but I'm still working on the Sierra's tune, now that I got the fuel pump replaced again (which, this time, I dropped the tank to swap it out... which has its own attendant issues. I'll cover that in a different thread.) :coffee:.

So... I'm deliberately keeping the Sierra off the road (and especially highway trips) until I get the tune sorted out. Now that the fuel sending unit issue is resolved (was slow to update), I can finish my tune, using a wideband sensor (yes, I bought one!) I also have a couple of other goodies (tools & parts) that I've been collecting for future use... those'll go in a 'build, pt. 2' thread. I'm thinking some "jaws may drop"... LMAO :shhh:

Anywho... after tomorrow, I should (?) have working A/C in the Sierra... and soon after that in the Envoy. Following up the rear is the one I'm driving the most right now (naturally)... the Accord.

Thanks again, guys. I'll update once I've got some cool air blowing on my sweaty brows 🥵
 

littleblazer

Gold Supporter
Well, that describes me to a 'T'... so I thank you (and recommend following the link, for the curious amongst us). I also saved the chart to my HDD, for future reference.

Believe it or not, that's one of the things that most annoys me... it's stressed that 'exactly' the right amount of refrigerant be used (+/- maybe 0.5lb ?) and yet nothing really exists to be able to measure the transferred amount (without spending $$$($) on pro equipment.)
I will definitely look into this. Thanks for the info.

Kudos to you (seriously, not sarcastic-like). For me, I compare $160 and 2hrs (if I'm lucky) to $185 and the same 2hrs for a completely new assembly... and I kinda go for the latter. That's what I found as well, when I was looking at clutch vs. new unit.

Seems to me that the price delta between clutch & complete unit didn't used to be so great (my age is showing here, I guess... but it really wasn't that long ago). Anyone else waiting to see if rescinded tariffs actually lower prices back down on goods from PRC? I'm guessing 'not' (and I don't want to get too off-track / political). Just my musings.


So... my latest...
Took the Sierra back outside, while I wait for it's new compressor (later today), and pulled the Envoy in. Yes... same 21-22" of vacuum. And as I suspected, it didn't hold -- in 30min, it lost all pressure. That's fine, I have seals, right?
As I got ready to replace them, the light bulb went on, and I realized that *this* was the right time to get a rear blockoff kit, even if that wasn't the source of the leak. Searched Google for the kit / info, and where was the best info? Right here, on GMTN, thanks to Mooseman's post from about a year ago. Ordered up a kit from the Bay, and it'll be here in a few days. Which now makes the Sierra the 'winner' in, 'which vehicle can deliver cool, refreshing A/C to me first?'

(For a couple of reasons) I felt like Thanos, in Avengers: Endgame... "You could not live with your own failure. Where did that bring you? Back to me." :hahano:
(as an aside... for some odd reason, I think that's one of the great movie lines of the last 20yrs or so)

So now I'm on hold again for a bit, until I get the new (to me) vacuum pump tomorrow from a guy on CL... a MAC-branded Robinaire, for $65. It's about 90min away, so I arranged a pickup time in the morning, before it gets too hot outside... LOL. And he'll demo how fast it pulls down to +29.xx in., before I hand over the cash. He advertised it as 'quick'. We'll see. I looked for a long time on CL, months ago, before giving up and buying the POS I got from Amazon. Wish this had been available, then. Oh, well...

(Yes, I could rent a pump, and save a few hours (and have a vehicle with working A/C to go pick the CL one up (I knew someone would bring that up)... but I'm still working on the Sierra's tune, now that I got the fuel pump replaced again (which, this time, I dropped the tank to swap it out... which has its own attendant issues. I'll cover that in a different thread.) :coffee:.

So... I'm deliberately keeping the Sierra off the road (and especially highway trips) until I get the tune sorted out. Now that the fuel sending unit issue is resolved (was slow to update), I can finish my tune, using a wideband sensor (yes, I bought one!) I also have a couple of other goodies (tools & parts) that I've been collecting for future use... those'll go in a 'build, pt. 2' thread. I'm thinking some "jaws may drop"... LMAO :shhh:

Anywho... after tomorrow, I should (?) have working A/C in the Sierra... and soon after that in the Envoy. Following up the rear is the one I'm driving the most right now (naturally)... the Accord.

Thanks again, guys. I'll update once I've got some cool air blowing on my sweaty brows 🥵
I'd have replaced the whole thing but the factory charge is still perfect and it blew ice cubes when I was done again. Company paid for it so I don't care and I made 400$ for fixing it. :redface:

The problem for me was that I needed to be done today. I knew I couldn't evac an AC system, replace the compressor and accumulator, and still have the truck back for that day working. And to get a compressor locally it was close to 300$. I looked online and it was cheaper bit being it's only noon right now and already 90 degrees or so... I think I made a good call lol. Like I said, not my money to spend.
 
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Update:

Good news -- after installing the compressor a couple of days ago, I now have cold air coming out of the vents on the Sierra. :woohoo:

(Tip for compressor removal: remove the A/C belt tensioner, release the trans cooler lines from their clip retainers (not from the radiator end, just the little bracket under the engine), and remove the unit via the front, under the truck. This works especially well if you've added PAG (compressor) oil recently, but found the compressor itself was shot -- because all the oil will still be in the compressor, and as soon as you tip / twist it to remove it from the engine bay... you'll be wearing the oil, facing a messy cleanup. Or swap the plastic plug from new to old, before tipping the compressor. Anyway... )

My new problem (?) is that the new compressor now doesn't cycle off. From what I can see, this could be due to: ambient cabin temp, a faulty low-side pressure sensor, or an overcharge of refrigerant (along with a couple of other things). After about 20min running & charging, I shut off the A/C while I researched the 'doesn't disengage' issue. I had the windows open, and the controls set on 'max cool' -- but even after I eventually turned up to '72F', the compressor was still engaged :confused:

Our 'mini heat wave' ended, and as I write this, it's 45F outside, and will be until Sunday. Brrrr! After it warms up a bit, I'll look into the cause of the thing staying engaged. I'm working on some other things on the truck until then.

Hopefully, it's not the pressure sensor, as I'm pretty sure I'll be looking at evacuating the system *again*, to change it out (from what I recall, I had to swap the switch from my old accumulator, when I replaced it). As far as the observed PSI... it seemed like it was slightly high, vs. ambient -- low side at about 50psi (ambient between 70-80F), and high side at about 275psi (?) So I'm a little worried about overcharging. I left the manifold gauges in place, and the system *did* equalize to ambient on both sides, when I checked it the next morning.

Oh, and the new (to me) vac pump worked well. When the guy I bought it from demo'd it, he had it hooked up to a manifold gauge set in what was a 'closed loop'... and it immediately went down to 29 in.
When I got it home, I found out I need to re-center the low-side gauge to '0', every time I use it (or add the 'notches' that it shows on the +0 side, to the inches of vac on the -0 side) Such is a cheap HF gauge set -- but it does work adequately, for someone like me.
As it turns out, had I done that from the outset, I might have seen the first pump take the vac down to 28-29"... but since I have a better quality pump now, I'll just use the 'new' one, going forward.

So that's where I'm at, now. Will update again with resolution of the newly observed non-cycling issue (but now 'always on', vs. 'always off') Fingers crossed that it's ambient / cabin temp related.
 

NJTB

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Does this happen only at idle? On mine, the low pressure guage reads about 30lbs.at ~80 degrees F and won't cycle. However, if I hold the throttle at about 1500-2000 rpm. it does, going from ~20 to 40 psi.
Hooked the guages up and laid them on the windshield to check. Gets cold, pressures were right for the temperature, so I didn't worry about it.
 

Mooseman

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Hopefully, it's not the pressure sensor, as I'm pretty sure I'll be looking at evacuating the system *again*, to change it out
There is a shrader valve under the sensor. Just unscrew and screw new one in. You might have a little refrigerant loss while unscrewing/screwing it.
 

aaserv

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I think its possible your pressures are out of whack. 50 is a lil high and 275 is way high. I would be hoping for something in the range of 35 and 160. I would definitely want to vacuum it down and measure the correct charge into the system and see what you have then. If the head press is still that excessively high you have other problems/s to look for...
 

TJBaker57

Well-Known Member
My new problem (?) is that the new compressor now doesn't cycle off


I would observe the high side pressure while in motion. Can be seen with Torque Pro or equivalent. I suspect you will find the system cycles while in motion where there is more airflow through the condenser.
 
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So... finally got a chance to finish this up. It's cycling properly. :thumbsup:

I did take a video of the manifold gauges resting on the windshield, and was going to post it here, but it's 212MB -- so I grabbed a couple of stills.

(unfortunately, Torque Pro only had the high side pressure, and it wasn't capturing / displaying it, even though I had the PID active - ran the test on the PID and got a 'no comms' message) So I had to go back to the actual gauge set, and got to do that today, after finishing some other things on the truck, earlier.

These were captured pretty much at the extremes of both sweeps.
System was verified equalized to ambient (almost 90F) on both sides before starting the truck and A/C (separately).

As you can see below, the low side cycles between 30-32psi and 50-55psi, while the high side cycles between 140 and 225psi. After verifying those readings against the chart, per my research... I'm calling it good. I might be off by an oz. or so of R134a, but that's actually acceptable, and I prefer that to trying to put 'just a leeeetle more' in (and potentially overcharging).

(Apologies for the washed out quality of the pics -- it's due to the strip light I have above my garage door. Tried to get it out of frame, but wasn't too successful.)

Lo_32_Hi_225_PSI.jpg

Lo50_Hi_140_PSI.jpg

So after I took the thing out for a drive, I noticed a couple of things...
- The A/C taxes this engine a LOT, for some reason. Nothing as far as a CEL or anything, but it's noticeable, IMO.

- I noticed while sitting idle for an extended period with the temp at 72F, that the system kicked into recirc on its own, after a few minutes -- guessing it was not cycling at idle, and finally some sensor kicked in to make the compressor come on. (yes, I have the auto climate)

- Finally, it looks like my next thing to fix will be the P/S pump, as it stopped providing assist at idle (even with the A/C off). Checked the fluid level after it cooled down; it's perfectly on the 'cold' mark. Checked the weep hole on the hydroboost unit I put in a few months back - it's fine. So I'll be researching that tonight. Oh, well... :book:
 

Chickenhawk

Well-Known Member
Don't worry about the recirc mode. It kicks it on automatically in conditions where water may be building up on the condenser. It will run like this for a few minutes to dry the water so that you don't get a musty smell in the cabin.

On our Trailblazers, GM added this capability in a PCM update somewhere around 2005 or so if I remember correctly. Anyone who had a factory update or a tuned PCM using the latest firmware will experience this. I get it on warm mornings where it was a humid evening the day before and I ran the a/c on the way home. It is weird, and it changes the sound and cuts out the a/c at the same time. I also notice the recirc light never actually comes on, even though that's the mode it goes into. Normal, unless it lasts more than a minute or two.
 

Mooseman

Moderator
So that's why the Saab used to do this whereas the 02 TB didn't. At least my 07 is the manual system. Haven't noticed it in the Avy yet.
 

Chickenhawk

Well-Known Member
No idea about a list of updates. I found it on a GM TSB many years ago, dealing with a musty smell when running a/c.
 
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Don't worry about the recirc mode. It kicks it on automatically in conditions where water may be building up on the condenser. It will run like this for a few minutes to dry the water so that you don't get a musty smell in the cabin.

On our Trailblazers, GM added this capability in a PCM update somewhere around 2005 or so if I remember correctly. Anyone who had a factory update or a tuned PCM using the latest firmware will experience this. I get it on warm mornings where it was a humid evening the day before and I ran the a/c on the way home. It is weird, and it changes the sound and cuts out the a/c at the same time. I also notice the recirc light never actually comes on, even though that's the mode it goes into. Normal, unless it lasts more than a minute or two.

I should've been clearer... the recirc wasn't a concern, per se, just an observation. Now, the P/S pump is a concern, b/c I'm going to have to replace it, after looking into it :hopeless:

A couple of additional notes on the recirc...
- This is in my Sierra, not the Envoy (just for clarification). The control heads are *similar* on both, but they do have some differences (I can take / post pics if anyone asks, but I don't think you will - ?) Not sure of the development cycle of either vehicle (e.g.; which was in development first / longest; their (total) featuresets are very similar, across the board). They're both '03s / SLTs.

- While my SOBs with auto-climate are smart enough to kick themselves into recirc (both at startup and at anytime the HVAC is on), this is the first time I remember one of my GMs doing so. Or maybe it's been too long since I've observed working A/C in one (about 2 summers for the Envoy, IIRC, and 'never' for the Sierra, until recently).

- What I did notice is that the air *did* get cooler when the recirc activated, and AFAIK, the A/C itself did *not* turn off. I'll need to pay attention if this ever happens again (and maybe the logic is covered in the service manual -- I'll need to check. If I find anything, I'll post back).
TBH, tho... it's more of a peculiarity ATM, and some other things are closer on my radar screen, so it'll be a bit until I come back to this; probably after I get the A/C leak fixed on the Envoy, so I can compare both, directly.
 

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