A/C Woes

[Mike534x]

I forgot to setup Torque to data log everything while driving home from work this afternoon.

With the truck idling/at operating temp, Torque is reading about 220-245 PSI. While driving *during moderator acceleration* it went up to 240-280. While coasting, I noticed the pressure would fluctuate a lot (this is where I question if its normal).

Temps today at 94* at 43% humidity.

Driving steady @ 40 MPH (with phone mounted in eye sight) these were the readings I was able to catch. I didn't catch the rate/how high it got during moderate/light acceleration.

230
240
224
228
230
200
198
190
185
200
215
218
220
236
245
255
225

Slowing down from 40 by letting off the gas/braking and staying at a stop (at this point I could feel the vents start blowing luke warm, before it switched back to being cool. It stayed at 50* from the vents, and would go back to 60* when coming to a stop, or slowing down.

190
198
170
160
130
142
140
130
124
150
170
180
200
230
250

I tried my best to memorize each point it reached, like I said I'm going to configure Torque to record the data logs for the high pressure side tomorrow, and upload them here to get a better/more consistent idea of how much its fluctuating.

 

[azswiss]

Had a similar situation on my '03 Suburban (w/ CJ3 RPO). The compressor would turn off when pressure dropped below 150psi (running the front blower only). By running both the front and rear blowers at full I was able to load the system sufficiently to keep the pressure above 150psi and keep the compressor engaged.

Edit: Adding link back to my post on this issue.
Leaky Schrader valve on AC System charging port

 

[TJBaker57]

Related, can one have multiple odb's connected / daisy chained in some fashion? sorry for the "side car".

ADDED: I see a splitter cable can be had

Indeed they can! I began with a splitter cable and then progressed to an extension cable which I added a splitting 'block' at the end It is just more convenient for my endeavors.

Now then, while one can add a splitter one can only have a single scantool (or equivalent app) operating at a time. If one tries more than one app or scantool it is like having 2 computers using the same network address if the analogy is familiar to anyone. It just doesn't work well.



What it DOES allow me to do is see the serial data traffic while another device is active. A second device can simply listen in.


So

I do know that you (tjbaker57) provided me with the more "accurate" output formula. One thing that I haven't done is compare the output to the launch data reader

That does sound familiar. I remember working out the formula and checking it against my old Refco Digimon digital manifold gauge set. Fortunately the precision of the high side pressure is not all that significant as will be evident in the graph I am about to post up.



At the left is steady state 65 mph and we see the high pressure side (red) cycling as it is designed to do with the low pressure "cycling switch". There is also see a value (green) that looks to coincide with the high pressure change.

That green line is PID 3701 [nope, it's 3702] (I think) and it shows things like the status of the low pressure cycling switch along with another data item called "A/C permission" which is either "granted" or "withheld". So what is being displayed by the green line is the low pressure switch activating and this makes the A/C Permission change from granted to withheld.

Check the legend on the left and just peruse the graph.

 

[TJBaker57]

I forgot to setup Torque to data log everything while driving home from work this afternoon.

With the truck idling/at operating temp, Torque is reading about 220-245 PSI. While driving *during moderator acceleration* it went up to 240-280. While coasting, I noticed the pressure would fluctuate a lot (this is where I question if its normal).

Temps today at 94* at 43% humidity.

Driving steady @ 40 MPH (with phone mounted in eye sight) these were the readings I was able to catch. I didn't catch the rate/how high it got during moderate/light acceleration.

230
240
224
228
230
200
198
190
185
200
215
218
220
236
245
255
225

Slowing down from 40 by letting off the gas/braking and staying at a stop (at this point I could feel the vents start blowing luke warm, before it switched back to being cool. It stayed at 50* from the vents, and would go back to 60* when coming to a stop, or slowing down.

190
198
170
160
130
142
140
130
124
150
170
180
200
230
250

I tried my best to memorize each point it reached, like I said I'm going to configure Torque to record the data logs for the high pressure side tomorrow, and upload them here to get a better/more consistent idea of how much its fluctuating.

This is a main reason why I really like the Car Scanner ELM OBD app. I don't have to "set up" much of anything to record data plus it graphs the data right there in the app.

 

[TJBaker57]

running both the front and rear blowers at full I was able to load the system sufficiently to keep the pressure above 150psi and keep the compressor engaged.

So what is really going on here is the added load of the rear evaporator and max fan speeds is enough to keep up the LOW side pressure above the cutoff point of the low pressure cycling switch. The high pressure plays no part in the cycling of the compressor. It will only trigger a compressor shutoff if the high side goes way up. BTW, if the high side goes high enough and the PCM fails to cutoff the compressor there is an overpressure relief valve that will pop off like the over-preasure valve on a shop air compressor tank.

 

[TJBaker57]

Here is another clip that shows the system as I arrived home and let it idle for a while.

This was my Yukon which has factory twin E-fans which you may be able to deduce from the graph.

 

[Mike534x]

Hooked up the mechanical gauges;

I'm seeing 55 PSI at idle, and 225 (high side needle fluctuates back and forth between 220-225).

I took a box fan and pointed at the front of the truck, and keep something pressed on the gas to hold it at 2k RPM.

As the low side drops to 22 PSI, the high side rises half way between 250 and 300....from there it drops after 5-6 seconds before getting to 53 and 151ish for the low/high side. This continues for the same duration of time.


I included a video, not sure if it helps any with seeing what its doing. Sorry for the wind noise, we're expected to have a bad storm this evening so I was trying to capture what I could while I still had daylight/before it rolled in. You can hear the compressor (kicking on and off???) in the background somewhat as soon as the pressure rises.

VID20240622180304.mp4

drive.google.com

 

[TJBaker57]

The high pressure plays no part in the cycling of the compressor.

Replying to my own statement !

I haven't read anything that says the high side does or does not have an effect on the cycling, I was again ASSuming things. But watching the OPs video I see his compressor cut back on at right about 150. And I 'think' that's about where my Yukon compressor was also coming back on today. Hmmmmm


EDIT: well hell, my memory is gone! Mine was cutting OFF at 150ish, not cutting back ON at 150 !!

 

[Mike534x]

This is such a bizarre issue. I've been reading for hours now, and I see mentions of an orifice tube restriction or condenser. Been searching for a shop that does A/C only repair, and I haven't found many nearby. I wish I had another 5.3 TB/Envoy to get a comparison reading off of, the pressures just seem too unsteady. I'd rather not part canon this by just throwing a new condenser or whatever else, and hope that fixes it.

Also not fond of my regular shop telling me that this is as good as its ever going to get, and to not drive it on hot days.

 

[AmpOverload]

That 221564 PID is not going to work, at least not with a 4. 2 engine. That PID ## is not supported. For a 4.2 you need a 221144 PID ##.

I know this is potentially "funny".... but it works on my 2008 4.2.... but I don't know where it came from in my travels.

Well this is good information! I had ASSumed that since it didn't work on my 2002, 2003, 2005 and 2006 4.2 PCMs that it wouldn't work in the others. It also does not work on my 2005 5.3 Yukon.

I don't want to go too far off-topic here, but on a 2008 TrailBlazer with the 4.2L engine, Tech2Win actually queries both PIDs, $1144 and $1564.

Here's the traffic I just captured showing the Mode $2C DPID $FA setup as proof:

RxID: 7E0  Data: 10 10 2C FA 13 6D 11 44
RxID: 7E0  Data: 21 15 64 11 6F 20 05 11
RxID: 7E0  Data: 22 54 19 40 55 55 55 55

And the Tech2Win "Cooling/HVAC Data" page shows "A/C High Side Pressure" twice, once in units of volts and again in units of pressure (kPa or psi). At first I thought that that might account for both PIDs being queried, but a similar test as a 2007 4.2L TrailBlazer has Tech2Win showing both variants (volts and pressure) but only querying PID $1144!

 

[Mooseman]

I wish I had another 5.3 TB/Envoy to get a comparison reading off of, the pressures just seem too unsteady. I'd rather not part canon this by just throwing a new condenser or whatever else, and hope that fixes it.

The engine size or type shouldn't make much of a difference between the two as the A/C systems is basically the same. Just the PIDs might be different between the two PCMs. The pressure differences would be caused by just about every other factor like compressor wear, debris in the system, airflow through the condenser and evaporator, temperature. The compressors themselves are basically the same except for the mounting and hose routing. Even idle speed is about the same.

 

[budwich]

Replying to my own statement !

I haven't read anything that says the high side does or does not have an effect on the cycling, I was again ASSuming things. But watching the OPs video I see his compressor cut back on at right about 150. And I 'think' that's about where my Yukon compressor was also coming back on today. Hmmmmm


EDIT: well hell, my memory is gone! Mine was cutting OFF at 150ish, not cutting back ON at 150 !!

Maybe that turns the "analysis" around. Is possible that the high pressure sensor works in both directions. Basically, cycling the system on and off ... on when the pressure is low but NOT as low as the low pressure "safety switch" and then off when the pressure reaches some point as determined by the pcm for the system and environment. Just my guess having never hooked up a full gage system and watched / listened to everything going on.

 

[Mike534x]

The engine size or type shouldn't make much of a difference between the two as the A/C systems is basically the same. Just the PIDs might be different between the two PCMs. The pressure differences would be caused by just about every other factor like compressor wear, debris in the system, airflow through the condenser and evaporator, temperature. The compressors themselves are basically the same except for the mounting and hose routing. Even idle speed is about the same.

I wasn't sure if there was difference between the two. That's the argument my regular guy keeps throwing at me, that it's because it's a V8 and the trucks black so it's too hard on the system to cool it off. I've told him that doesn't sound right, and I would expect the Envoy to blow cold like the Trailblazer..or at the very it should with the system being new. My only assumption at this point is that the first shop didn't flush the system, and there's crude in the lines that may or may not be traveling through and plugging up the condenser and orifice tube (maybe evaporator too?). The radiator facing the clutch has a few bent fins in some spots, but not enough to block air flow or even overheat.

I suppose all I can do is get the system taken down, and pull the lines from the compressor/condenser, orifice tube, and the liquid/suction line to the accumulator and try flushing solvent through it and see if any crude comes out. If those are clear, then it may prove that the condenser is full of debris from the old compressor.

 

[budwich]

I forgot to setup Torque to data log everything while driving home from work this afternoon.

With the truck idling/at operating temp, Torque is reading about 220-245 PSI. While driving *during moderator acceleration* it went up to 240-280. While coasting, I noticed the pressure would fluctuate a lot (this is where I question if its normal).

Temps today at 94* at 43% humidity.

Driving steady @ 40 MPH (with phone mounted in eye sight) these were the readings I was able to catch. I didn't catch the rate/how high it got during moderate/light acceleration.

230
240
224
228
230
200
198
190
185
200
215
218
220
236
245
255
225

Slowing down from 40 by letting off the gas/braking and staying at a stop (at this point I could feel the vents start blowing luke warm, before it switched back to being cool. It stayed at 50* from the vents, and would go back to 60* when coming to a stop, or slowing down.

190
198
170
160
130
142
140
130
124
150
170
180
200
230
250

I tried my best to memorize each point it reached, like I said I'm going to configure Torque to record the data logs for the high pressure side tomorrow, and upload them here to get a better/more consistent idea of how much its fluctuating.

maybe your actuators / air flow controllers have an issue?

 

[Mike534x]

maybe your actuators / air flow controllers have an issue?

They seem to be working as they should when cycling through the different modes. I don't hear any sounds/changes from the actuators/doors, or anything of that sort when it's blowing only when switching where it blows.

 

[budwich]

So you have the "where" and "when" but what about "what"?
There can be issues with the "what" such that heat is not shut off in the "what" mode because the door is "freewheeling a bit".

 

[TJBaker57]

Maybe that turns the "analysis" around. Is possible that the high pressure sensor works in both directions. Basically, cycling the system on and off ... on when the pressure is low but NOT as low as the low pressure "safety switch" and then off when the pressure reaches some point as determined by the pcm for the system and environment. Just my guess having never hooked up a full gage system and watched / listened to everything going on.

In these systems I believe the primary purpose of the low pressure switch is to prevent icing of the evaporator by cutting off the compressor when the low pressure reaches the point where icing is possible or just before that point. Google up an r134a temperature/pressure chart and it will be seen the relationship between pressure and temperature for r134a puts the freeze point right about 26, 27 psi. No coincidence that this is roughly where the low pressure switch activates.

 

[Mike534x]

So you have the "where" and "when" but what about "what"?
There can be issues with the "what" such that heat is not shut off in the "what" mode because the door is "freewheeling a bit".

One of times I wish I had a tech 2 on hand to test, and verify each door and actuators function. Its always been quick to defrost during Winter, and I'm not noticing any issues with the windshield or windows experiencing any fogging up with it set to run at Auto/Manual full blast. I suppose to rule out the doors and actuators, I could try pulling the HVAC fuses and let the climate control head, and actuators reset and go through the recalibration and see if it makes any difference.

Only thing I've really noticed it doing, is that when it's blowing cool while driving and slowing down to a stop/or coasting there is a minor "hiss" sound that comes from the vents when it stops blowing "cool" for a moment like when the compressor cycles off causing my vent gauge to fog up a bit right as it blows cool again. I was noticing that the accumulator doesn't get as cool either when the air from the vents sits at the 60* mark on the gauge.

 

[budwich]

That still sounds like the clutch is not functioning well. The "hiss" is somewhat "alarming" as I don't know of any "vacuum actuated" items on these vehicles like in other older vehicles. That "hiss" may mean a gas release somewhere which ultimately mean the charge is not as expected.

Having said that, it could be just some water / condensation dripping onto some thing hot somewhere.... maybe dripping on the heater.

 

[Mike534x]

The sound is hard to describe, I've ever heard it on the Trailblazer (where its ice cold, starts getting warmer back to cold).

Driving home from work I've noticed the A/C is working...bad. Its only 70* with 80% humidity. Temps from vent at idle were 60* straight, dropping sometimes to 48* on the ride home. It was worse when coming to a complete stop.

Got home, popped the hood and tried feeling the lines going to the evaporator core after noticing the accumulator was just slightly cool. Shut her down, and walked around and heard a hissing sound. Thought it was the accumulator, but it went away after 4 seconds. Started it, let the system kick on and waited and shut down. Listened closer and thought it was the coolant reservoir. Nope....listened more and went to grab the accumulator and it got louder before stopping. Hmmm.....started it again, shut down and started tugging on the accumulator it would get louder and quieter each time I let go. Did it one more time and noticed the sound was loudest coming from the rear corner between the reservoir and accumulator. Started it up one more time, and shut her down.

I only know one line runs between that area, and its the suction line. Did my test again, and with it off took a socket extender and started pushing down on the line in that area and was getting a loud hiss again. Started her up, got as close as I can get and hear it "hissing", pressed it and peaked inside and saw the temps from the vent slowly rise.

So the issue seems to be a pinhole leak in the elbow of the suction line where its encased in its sleeving, if thats the case, the sleeving must be soaking in the dye making it impossible to track down the leak.

 

[TJBaker57]

FWIW, look at a temperature/pressure chart for r134a. You stated the outside temperature was 85. Likely hotter in the engine bay but let's use 85 F. At that temperature r134a will only remain in the liquid state if the pressure is greater than about 95 psi. As soon as the pressure drops below that the liquid r134a will start flashing to a gas. This will be heard as a hiss that comes from inside the refrigerant piping. Chances are great that the liquid refrigerant is actually quite warmer than this 85 F and thus the pressure required to keep it in a liquid phase is a good deal higher than the 95 psi we just spoke of.

Bottom line here, it is absolutely normal for refrigerant lines to hiss when the compressor is shut down.

 

[Mike534x]

Understood, but is it normal for the hissing to audible while the compressor is running? Like I had mentioned. There's a faint hiss coming from the suction line that runs behind the coolant overfill tank, and accumulator. I noticed that when the system is off you can hear it, and even touching the line results in it getting louder. Whenever I touched the line to make it louder resulted in the temps from the vents blowing warmer while the system/compressor is already running.

 

[budwich]

does it hiss on your other vehicle?

 

[TJBaker57]

Understood, but is it normal for the hissing to audible while the compressor is running? Like I had mentioned. There's a faint hiss coming from the suction line that runs behind the coolant overfill tank, and accumulator. I noticed that when the system is off you can hear it, and even touching the line results in it getting louder. Whenever I touched the line to make it louder resulted in the temps from the vents blowing warmer while the system/compressor is already running.

I think if a leak is large enough to be heard, it will disable the system in a matter of hours.

Also, if a leak is in a suction line,,, that leak should be greater when the system is OFF rather than ON because the pressure will be higher in the suction lines when the system is OFF.

Just some thoughts that run around in my grey matter.

 

[Mike534x]

It makes perfect sense when you put it that way, it's more so just confusing to me why it's doing what it's doing. After messing with it at lunch, it'a only blowing cool when the engines RPM is increased otherwise it's barely cool at idle.

Thats the odd part, I would imagine it should be louder when it's off. Why its louder when I touch it is beyond me, regardless the leak has to be originating from that area. I'll need to check the low side and high side pressure again on the gauges.

 

[Mike534x]

does it hiss on your other vehicle?

On the Trailblazer it does when the compressor kicks off, but the sound doesn't get louder when wiggling the suction line like I'm experiencing with the Envoy currently.

 

[Mike534x]

Received the new A/C Condenser, and suction line for the Envoy. Went with a Denso unit, wasn't sure on the quality for the other brands listed. The Denso unit seems nearly identical to the OEM one going off the pictures. However, I did notice that on each side where the fins meet the tubes (sorry don't know the exact name for it) I'm seeing little specs of neon green between the fins. Which is making me wonder if there's a small leak in the unit itself. I tried nabbing pics but its not showing up too well on camera. Suction line I went with a four seasons unit that included the orifice tube. I did nab an ACDELCO 1550121 VOV Orifice Tube, but I may send that back. The reviews seemed hit or miss, but was mostly sold on the "improved cooling" capacity at idle, but I may stick with the regular type.

Temps were about 75* with 40% humidity, and the compressor was cycling on/off while driving home from work this morning. Blew cold as long as my foot was on the gas, and soon as I let off to coast it started to blow luke cool. Would that indicate a possible low low-side pressure?

The Hayden 2851 thermal clutch is working great, though I'm not used to hearing it engage for the first two minutes during start up...but it does kick in a usually during long idles/sitting in traffic. So that's a plus...not bad for a $49 unit.

I should hopefully have the Trailblazer back Monday, so I can get the Envoy taken down and work on the condenser while we have a cool week coming up. My guy nagged me about the new "used 40k mile" compressor, but its a chance I'm willing to take....especially if it actually stays running compared to the old one.

 

[BigSilver]

Alrighty! So I don't throw off the "What did you" thread, I made this one to post the issues I'm having and what's been done. This thread will cover both trucks, but the main focus will be on the Envoy.

So a run down of what's been done;

Envoy
- New Denso A/C Compressor, and AC Delco Dryer/Accumulator as of 6/13/24
- A/C Recharged twice in Summer of 2023 (Shop that services our work vehicles did the service, still didn't blow super cold. Second shop that does our alignments/most of the work looked it over and said it was overfilled. Blew cool, but not cold cold. Temp gauge attached to the center vent showed 70*, and 55-60*F being the coldest with Auto-HVAC set to 60* with re-circulation/max fan.
- EV Fan Clutch swapped to a Thermal Clutch (Used unit pulled from a 2008 TrailBlazer) as of Summer of 2022
- A/C Condenser replaced in Summer of 2017. Shop found a hole where it blew, and send debris into the system. Worked "somewhat" okay but gradually got warmer as the years went by.

A/C worked fantastic in the Envoy after the new compressor and accumulator were installed, took 5 minutes to blow ice-cold but no biggie. The shop is roughly 40 minutes away from home, and the temp reading I was getting from the gauge stayed at around 42-48*F, which is a significant improvement over the last few years. I did notice that the air got less cold at idle/at a stop, where it would go to 50-55* but would drop back down again while moving. Fast forward to today, left the house at 9 AM to run errands/shop and the ambient temp outside was 92* F. Got in, A/C started blowing immediately cool, got about 10 minutes from home and she was sitting at the same readings (42-48* while coasting) beforehand. Pulled into the shopping center, got out, and got back in about an hour later. Noticed its not blowing as "cold" as it did leaving home. Continued driving around, and the gauge was reading 60*F from the vents, even with the recirculate button on (could hear the change in the actuators when pressing it). Drove around some more, and the gauge fluctuated between 55-60*. Noticed that during the fluctuations, I could feel the air getting "slightly" warmer, with that brief "smell" (I can't describe it well) that comes when the compressor cycles off/and it stops sending cold air through.

So now its underperforming, and almost acting like it did the prior summers before it failed. Some suggestions were testing the fan clutch, so if its doing this in stop and go/semi-city driving....would it be better on the highway? Not exactly. I figured if the clutch is acting up, then taking it on the highway with more airflow hitting the condensor should compensate for it (at least thats what I assumed). Drove for about 35 minutes with no traffic, and it took 30 minutes before the air from the vents finally was reading 48*.The moment I got off and came to a stop it shot up to 60*.

Which has me questioning, is the system overfilled, or undercharged?
Did the shop replace EVERY seal as instructed (including the high side at the condensor, not just the compressor/accumulator)
Did they replace the orifice tube and valves (I provided those in the package with the new A/C belt and tensior)
Is my 7 year old A/C Condensor junk/clogged from whatever made its way into the old system?
Thermal Clutch is spinning enough to prevent an overheat, but not engaging to fully move air through the condensor?

At operating temp, it does feel like the thermal clutch is working. When attempting to stop it, it did take some effort to slow it down, but not stop it. I did notice it took a bit a brief moment for it to "catch" and spin back up to speed. It certainly looked and felt nothing like the old EV clutch that just gave up on spinning fully after stopping it. One thing I found odd is, it doesn't roar on cold starts after sitting, or even hearing it on hot days. Operating temp sits between 204-209, so its not overheating.

Was the system fully evacuated prior to recharging it again by the shop?

 

[Mike534x]

Update:

Took Envoy this morning to have the system evacuated.

Found some problems with the first shops install, that I believe fully contributed to the issues I was having. For starters, the seals were not replaced on the condenser. Pulled the upper suction line, and the one that runs to the compressor and they were the original seals (corrosion, and the junk thats been slowly seeping out). Upon opening the old suction line, they didn't even install the new orifice tube correctly. They literally put it in backwards, and it was just sitting inside the line where it joins and tightens up. There was also what looked like a small hair ball attached to the tube itself, so no idea what the hell that is or where it came from. Installed the new accumulator, and replaced the seals that run from the evaporator core to it. New condenser was put in, as well as the seals. I couldn't find a definitive answer for how much oil it took, so I aired on the side of caution and added about 1.5 ounces of PAG 46 oil.

Just waiting on the call for the Trailblazer to be ready, so I can swap it and have them recharge the Envoy and do a pressure test on it. So to hopefully get some money back from the first shop, I'm going to see if my guy can make up an invoice with what I found, and use that to raise some hell for doing such a shoddy job.

 

[Mike534x]

Update 2:

Trailblazer is ready, and seems to be working with the "new" compressor. There was a slight issue with the connectors, I guess the original used a 3 pin, and the one I got from the wrecked 07 was a 2 pin. They cut the connector off the old compressor, and put it on the new one and so far seems to be working without an issue. I've got the old one, so I'll be ordering the one from aliexpress soon to do a rebuild on it, and keep it as a spare.

Envoy was ready too, no leaks, or issues with it holding pressure. Didn't get a good chance to test either of them. We're supposed to be back in the 90s again this week/early next week so I'll be able to report back with how they're both doing.

 

[TJBaker57]

I find it curious that in the automotive field they leak test refrigerant systems with pressure. In the commercial and residential HVAC industry we test with vacuum. Very deep vacuum that cannot be even measured with a standard set of manifold gauges. It requires an electronic vacuum gauge that most often meaures in microns (of Hg).

 

[Mooseman]

They are tested either way. Automotive A/C machines do test by putting a vacuum to the system however a leak detector can also be used to pinpoint the leak, especially in an inaccessible location like the evaporator.

 

[TJBaker57]

They are tested either way. Automotive A/C machines do test by putting a vacuum to the system however a leak detector can also be used to pinpoint the leak, especially in an inaccessible location like the evaporator.

True. We do use pressure to help locate a leak but using pressure as a leak test is unreliable for 2 reasons. Even in a leak free system pressure changes with temperature, that pesky "ideal gas law" and all. Secondly, you must do a deep vacuum test anyway to prove that absolutely ALL moisture has been removed from the system.

The vacuum test is important enough that for one supermarket chain we did the HVAC for (not the refrigeration) the contract douments stated that a representative of the engineering firm must visit the site to witness and sign off on the deep vacuum test. I would triple evacuate the system to the neighborhood of 100 microns. (this took days for a 20 ton system with 2" copper suction piping) The system was then valved off and the vacuum must hold for 10 minutes.

Only a deep vacuum test can prove a system is free of moisture.

Perhaps automotive systems are just not capable of holding such a deep vacuum? I only got to the mid 500s when I last did mine.

 

[xavierny25]

True. We do use pressure to help locate a leak but using pressure as a leak test is unreliable for 2 reasons. Even in a leak free system pressure changes with temperature, that pesky "ideal gas law" and all. Secondly, you must do a deep vacuum test anyway to prove that absolutely ALL moisture has been removed from the system.

The vacuum test is important enough that for one supermarket chain we did the HVAC for (not the refrigeration) the contract douments stated that a representative of the engineering firm must visit the site to witness and sign off on the deep vacuum test. I would triple evacuate the system to the neighborhood of 100 microns. (this took days for a 20 ton system with 2" copper suction piping) The system was then valved off and the vacuum must hold for 10 minutes.

Only a deep vacuum test can prove a system is free of moisture.

Perhaps automotive systems are just not capable of holding such a deep vacuum? I only got to the mid 500s when I last did mine.

View attachment 113811

My 2 pennies here. One thing to note is that in the automotive field you have rubber hoses, I've personally never seen rubber lines in commercial/residential hvac. Unless you count the lines on the manifold gauge which are never left on the system permanently.