could AC cutout be related to thermostat?

meerschm

Original poster
Member
Aug 26, 2012
1,079
had a brain fart earlier today i want to run past you.

last spring I replaced the thermostat, old one was too cold. temp seems ok, but with the new thermostat, the AC got flaky, when very hot (at first when 100 and in traffic, by the end of the summer, would happen on an uphill run to work in the high 90s, with humidity)

a few threads here discuss some thermostats which do not open well. i was thinking if the coolant flow was restricted, it could get too hot, and the computer would turn off the AC compressor to save the motor. a couple times I noticed the temp gauge inching up a bit as the AC cut out

( I guess I am a little fuzzy on how hot that would have to be)

i now have some software which should be able to catch the details. so when it does finally get hot, might be able to figure out exactly what is up, and if it seems connected, or just a few old AC clutch coils.

do you think if the thermostat is not opening up all the way it would cause the AC to cut out?
 

meerschm

Original poster
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Aug 26, 2012
1,079
just looked up my paperwork, the thermostat I put in is a Gates 33939 was under $20 at rock auto last March.
 

c good

Member
Dec 8, 2011
521
Not related to thermostat. These older model compressors start to get a weak compressor clutch coil assembly, as you have noted. The "airgap" can be reduced by pulling off the front of the clutch assembly and pulling out the shim. Sometimes this will solve the problem. Otherwise you're looking at a new clutch assembly (if you can find one) or replacing it with one from a junkyard compressor. Mine had this problem, but there were so many miles on the compressor I just went with a low mileage used (new to me) compressor from salvage yard. It's worked perfectly ever since....

What a nightmare it was....right when things got hot out, the compressor would just disengage. When temps were below 85 degrees the thing would work perfectly....freeze you out of the vehicle...Finally figured it out as the clutch coil assembly.....HTH c good
 

CaptainXL

Member
Dec 4, 2011
2,445
meerschm said:
do you think if the thermostat is not opening up all the way it would cause the AC to cut out?

No, but if it is hot out and the high pressure side gets too high it will turn off the compressor which will mimic it. It's not related to engine temp. Have you had the AC checked for proper fill of R134A? You should have it initially filled by volume and not pressure.
 

meerschm

Original poster
Member
Aug 26, 2012
1,079
I had the system emptied and filled by weight, including a leak check dye. also changed the low pressure switch. my Fan clutch replacement was also motivated by this issue. (which it did not solve)

can you buy a compressor clutch anywhere? just from a salvage yard?

( I sent an e-bay message to airpartsinc. Guess I can wait and try a few other places if I find any ---hint hint, suggestions appreciated--- I hesitate to tear into the R134a plumbing if I don't have to.)
 

c good

Member
Dec 8, 2011
521
Clutch assembly is specific to the compressor. I searched extensively for a new one on line, etc but could never come up with just the clutch assembly. that's why I went with a salvage yard one. I would try removing the shim first to see if it solves the problem. Others have had success with this method.

Best way to absolutely confirm a weak coil assembly is to try pushing on the front of the clutch with a stick when the compressor cuts out. It should get it close enough to grab and engage the compressor. Just be extremely careful not to get the stick, ( I used a broomstick handle)in the serpentine belt or other rotating parts. By using this method you will confirm there is power to the coil assembly. HTH c good
 

meerschm

Original poster
Member
Aug 26, 2012
1,079
If the coil is only weak, or slips, that would be the way to go. hard to troubleshoot since it only happens so far when the temps are well over 90.

I guess a weak coil would result in pressure increase and then shutoff. (if the coil was weak instead of electrically opening up when hot)

They sent me an e-mail saying the techs would put together a kit when they get back in next week if they have the parts in stock.

I will let you know what they come up with. might need a trip to one of the local Harbor Freight stores to buy some snap ring pliers

thanks for the feedback.

:smile:
 

c good

Member
Dec 8, 2011
521
compressor having a weak coil has nothing to do with over pressure in the system. A weak coil simply does not have enough strength to engage the clutch plate and keep it engaged. Thus the compressor will not spin.

The coil assembly does get weaker as it gets hotter. Mine would cut out, actually go "open" with temperatures over 85 degrees outside. I spent weeks, and over $300 at two different dealers and they never figured it out. I finally took a spray bottle and would hose down the front of the compressor to get it to engage. Then a friend of mine told me to try the broom stick method. That solved the mystery.
 

meerschm

Original poster
Member
Aug 26, 2012
1,079
c good said:
compressor having a weak coil has nothing to do with over pressure in the system. A weak coil simply does not have enough strength to engage the clutch plate and keep it engaged. Thus the compressor will not spin.

The coil assembly does get weaker as it gets hotter. Mine would cut out, actually go "open" with temperatures over 85 degrees outside. I spent weeks, and over $300 at two different dealers and they never figured it out. I finally took a spray bottle and would hose down the front of the compressor to get it to engage. Then a friend of mine told me to try the broom stick method. That solved the mystery.


I see your point, it is not a case of clutch slipping and not pumping fast enough, either it spins the compressor or not. (and the clutch is supposed to cycle off and on many times in normal operation, depending on load conditions and demand)

( I just changed the belt on my washing machine, which was ten years old and suspected of slipping a bit. quite a different application.)
 

c good

Member
Dec 8, 2011
521
Great Find! I looked everywhere (albeit a few years ago) and couldn't find one of these anywhere. This should solve the problem. Please keep us posted. c good
 

meerschm

Original poster
Member
Aug 26, 2012
1,079
Guess I will have to pick up a pair of snap ring pliers and take the fan clutch and fairing out again.

( I might try with the fan in, but it looks pretty tight)

will be a couple weeks before I dig into this anyway. will let you know how it goes.
 

c good

Member
Dec 8, 2011
521
I don't think you'll have to take the fan clutch off. Pretty sure you can get to it from the bottom (IIRC) with just taking off the fan shroud. A little 3/8" drive air rachet works perfect for knocking the nut loose on the front of the compressor. Good luck and keep us posted. Cam (c good)
 

meerschm

Original poster
Member
Aug 26, 2012
1,079
Thanks for the hint on the air ratchet. Always glad to have a good reason to fire up the compressor.

can you really get the fan shroud much out of the way without taking off the fan clutch, fan, and opening up the upper radiator hose?

:undecided:
 

meerschm

Original poster
Member
Aug 26, 2012
1,079
just back from a ski week my wife won.


the A/C clutch got here before we left, but had to wax and sharpen the ski edges. (it was 90 here in VA, but the snow was flying in Colorado)

anyway, today i took her out for a short drive, and no A/C. my cheapy single gauge (the kind that attaches to a freon can and the low pressure port) shows the compressor cycles on and off, pressure bobs between 50 to 25 PSI..(just to the edge of the green) (which I can see by looking at the front of the compressor) works enough to cycle the low pressure switch. on and off. I suspect now that there is some leak of the R134a. I am rethinking the problem. I could have it recharged and see how it does, then troubleshoot when it hits 95 or so, to verify if the clutch coil is going bad.

perhaps it would be better to order a compressor, dryer and orifice. any other parts to change after ten years?

any suggestions?
 

c good

Member
Dec 8, 2011
521
You need a full set of gauges to read both high and low side pressures. You really need to verify both low and high side pressures before you can determine any course of action. I thought from your previous posts that this was already done. If you have proper pressures on both the low and high side ports when the compressor is running and you've already replaced or tested the low pressure cut out switch, then you've got a bad clutch coil assembly. Heck, if you got the cash to ski in Colorado..just take it to an AC shop! :smile:

Start with the basics...c good
 

meerschm

Original poster
Member
Aug 26, 2012
1,079
I had the TB filled with R134a by weight with leak check added last summer. (and verified proper operation) after that, it did cut out a couple times, but only when it was very hot (over mid-90s, with some idle time in traffic, or up long hills) of course this was fully loaded on the way to the beach, with an impatient wife. would cut out in 98 degree hot slow traffic, but come back after we started to move.

after getting home from that trip, I updated my diagnostic software, so I could see what was up, but the weather cooled off. (hard to troubleshoot a working system)

was going to verify as soon as the weather warmed up. now must have a slow leak to figure out as well.

I will probably stop by the firestone place I had fill the freon with leak check and see if they can see the leak location ( I took a quick look last night with a UV designed to see cat urine, but did not see any leak evidence) it could be the last trip in the winter road salt which I rinsed off also took any leak dye evidence with it.

might invest in a double gauge set and vacuum pump. have not been to Harbor Freight in at least a week. :smile:

the ski trip was a one time good deal. wife was in a ski race in Jan at Pico in VT (which we drove the TB) they had a promotion that had them sign up in six person teams, random drawing for 5 days lift tickets and lodging at Copper. she won, step son had school, so I took his place. we flew on points and miles, (plus $100 or so) plus an AARP rate rental car for $110, and $50 gas money. pretty cheap trip, and it snowed most days.View attachment 27444 you can see I-70 in this photo.

we both managed to avoid any serious injury so a nice trip.

I could take it to a shop, but still stinging from paying last summer to have the fuel tank dropped to change the leaking fuel pump. I am afraid the cost to fix the AC reliably would come to half the value of the truck!
 

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meerschm

Original poster
Member
Aug 26, 2012
1,079
OK stopped by wally mart today and picked up three cans of 75000 miles plus R134a, and my goodies (vacuum pump, Gauge set and can tap) came from Amazon.

so I charged up the TB

View attachment 27546
vacuum pump

View attachment 27547View attachment 27547
all hooked up (was not much left so I vented the last 20 psi)

View attachment 27548



pulled down pretty close to -30 psi

View attachment 27549

View attachment 27550

ambient was 75 degrees and 60 % RH. sorry for the fuzzy photos, used a flashlight and my cell phone camera. serves me right for working after dinner this time of year.

( I used a scale to measure how much went in. ended up probably two ounces under the 30 oz spec, but pressure was a little higher on the low side.)

when filling up, the compressor did not cycle at first, till after the first can and part way into the second. cans held 11 oz R134a and 1oz oil and leak stuff.
use of a bucket of hot tap water helps motivate migration of the refrigerant from the can. (place the can into a part full bucket of hot tap water)

low pressure switch cycled fairly regularly until almost the end of the second can.

when closer to full, the compressor stayed on. no cycling. HVAC control set for 60, windows open, fan on high.

now to drive her a couple days and see how it works.

when it hits 90 I can see what makes it drop out.

more later. ( I will hook up the gauges in the actual sunshine Saturday for a better photo or two.)

Mike
 

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CaptainXL

Member
Dec 4, 2011
2,445
Isnt it only like $50 to have a shop evacuate a system? I was debating getting a vacuum pump but it seems kind of a waste. Especially if only using it once in a millenium. Did you change the receiver drier and orifice tube? I would have pressure tested with nitrogen as well.

Many times (as in my case) poor ac performance can be the result of too much moisture in the system. In which case I had the sytem evacuated had the drier replaced . Then they refilled per temperature spec tables in the service manual. Hope it works out for you.
 

meerschm

Original poster
Member
Aug 26, 2012
1,079
around here service at the on base hobby shop is $100. shops charge more. since I have had to fill this twice, I suspect I shall have to again. esp if it leaks bad and I have to open up the system. probably an optional purchase, in the use it twice or three times to pay the difference. biggest part is enabling DIY maintenance.

interesting to me is that after pulling the vacuum, it took a few ounces less than stated capacity to get the pressure. I suspect that the last shop filled by pressure, not weight. this would leave the system underfilled.

the R134a I used has an anti-leak additive, so perhaps it will stop the slow (like a year) leak.
 

c good

Member
Dec 8, 2011
521
Looking good so far. Did you do a leak down test after pulling vacuum? It's always a good idea after pulling vacuum to close off valves and let it sit for about 15 minutes to see if you lose vacuum. That will pretty much verify a leak. Won't locate the leak, but will verify it. I've had good luck with the sealer type 134 so unless it's a catastrophic leak it should seal it up. Thanks for keeping us posted. c good
 

meerschm

Original poster
Member
Aug 26, 2012
1,079
I figured it had held over 30 psi for the weeks before I worked on it, so a 15 minute -30 PSI test would not tell me much more. (and I did run out of daylight.) I did not disturb any of the refrigerant lines, except to connect to high and low side ports.
 

CaptainXL

Member
Dec 4, 2011
2,445
The problem is that refrigerant is subject to temperature differential (expansion/contraction) and nitrogen is not for the most part. That's why professional AC installers use it. And the system is pressurized up to the max test pressure (usually 1.5 - 2x the working pressure). In our case close to 300 psi. Nitrogen is also used in brazing lines to displace oxygen and prevent formation of soot in lines. I'm not saying what your doing is not gonna work but you will never find a small leak doing it this way. Most of the time you can use a blacklight in the dark to search for leaks. The refrigerant comes with green fluorescent dye to aid in tracking leaks.
 

meerschm

Original poster
Member
Aug 26, 2012
1,079
Thanks for the advice.

in my case I do not think there is a huge leak, and in fact, think it possible the sealing additive may do the trick. last summer, I did have the fill include added fluorescent dye, which I understand is in the oil, which I do not think leaked out. I suspect the refrigerant leak is likely from the ten year old seals in the compressor. (pure wag on my part...wag stands for wild ass guess)

good point about checking in the dark, will take a look after it stops raining...

the real complaint is that last summer the otherwise fully functioning a/c dropped out when it was 100 and we got stopped in traffic. If can verify this happens when the clutch is still signalling to operate, I will replace the compressor clutch. I do plan to get the feeler gauges out to check the gap in the clutch..
 

meerschm

Original poster
Member
Aug 26, 2012
1,079
Here are the better photos I promised.

when I tried this last week, it was sunny but cooler and the compressor was cycling. I then noticed the high pressure hose on the gauge set I ordered from Amazon was leaking, between the fitting compressed on the hose and the one that hooks to the adapter for the vehicle. bubbles, oil, leak detector fluid... pissed me off.:hissyfit:

I looked at night with my UV flashlight, and saw some glowing around the joint between the condenser and the high pressure hose headed for the accumulator. picked up a $5 seal from mr goodpart.

today the Amazon package came, so I hooked up the new hose with the older gauge set.

I was surprised that it looks like the AC is working ok. (glad I did not dig right in to the plumbing)

View attachment 27728
have to know the ambient.

View attachment 27729\

chart from the service manual.

and after ten minutes or so with a couple doors open, temp set to 60, full fan on,

View attachment 27730

Looks a little low on the high side, but I think it is ok. it had been sunny before, so I think the TB was a bit over ambient temp. (service manual wants you to park inside or in the shade)

and just to check on how it really works,

View attachment 27731

Now I just need a 95 or 100 degree day to see if I the clutch is weak.:smile:
 

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triz

Member
Apr 22, 2013
746
I had my AC Clutch Seize on me on a trip from Florida to Texas. Nothing like a new belt snapping at like 1am on I-10. I was able to get a brand new ac compressor with new clutch for 175 bucks at Advance Auto. Symptoms were similar. AC would work periodically and sometimes blow hot. Then a slight noise. On the trip the clutch actually melted.

All I can say was glad I had AAA.
 
Dec 5, 2011
570
Central Pennsylvania
If your A/C is still acting up I would seriously consider checking the clutch and the clutch mating surfaces.

Here's what happened to me:
Intermittent A/C - worked wonderfully well in temps below 85-90, above not at all.
One day, I decided to observe operation of the clutch (after some troubleshooting to verify wiring was all good - it was). I cold see the clutch ATTEMPT to engage (the gap between the clutch plate and the pully got slightly smaller) but the clutch plate wouldn't spin. I knew my compressor was not seized. I removed the clutch plate and discovered the pullyside clutch mating surface was deeply gouged in a pattern that matched the clutchside mating surface. With a dremel I was able to grind the circular ridges flat and basically make the pulleyside mating surface flush/flat again. I would have preferred to take the pulley itself to a machine shop and have it "decked", but found the dremel did a good enough job of it. After reassembling everything, minus the airgap shim, it worked perfectly.
A link to my (albeit sparse) thread: http://gmtnation.com/f23/yet-another-c-thread-clutch-seriously-worn-3906/.

My fix was in June of 2012 and I haven't had one problem with it since. And I had MANY days in the 90+ range. With 130,000 or so miles on this thing, I'm not about to soak $1000 into the A/C if I don't have to. The simplest (cheapest) fix that works, for me, is what I go with - but to each their own.

I saw you ordered a clutch but haven't installed it yet. I would do that before anything else - if that fails to solve the problem, then maybe a compressor - but my money is on the clutch.
 

meerschm

Original poster
Member
Aug 26, 2012
1,079
Thanks.

my plan is to verify what is wrong before swapping parts. (unique approach, i know.) I was out today configuring my scan tool software to capture the AC related info. when it warms up I want to verify that the system is asking for the compressor to work and it is not. (would hate to dig in if it is something else, like a hot transmission or something)

I like your suggestion that it could just be the increased gap in the compressor clutch. said I was going to gap it, but did not do so yet. I think I read it is supposed to be .050 inches or so. I think I have a set of feeler gauges someplace.

if/when I get it to stop, i may try to pull a shim and if that does not work, change the compressor clutch.

I was going to just go ahead and change the clutch, but not sure it can be done without pulling the fan and shroud (with the fan clutch) and we all know what a minor pain that can be.
 

triz

Member
Apr 22, 2013
746
You might be able to drop the compressor a bit to give you enough to be able to get the clutch off. I cant remember how much slack there was left.
 

c good

Member
Dec 8, 2011
521
TequilaWarrio said:
If your A/C is still acting up I would seriously consider checking the clutch and the clutch mating surfaces.

Here's what happened to me:
Intermittent A/C - worked wonderfully well in temps below 85-90, above not at all.
One day, I decided to observe operation of the clutch (after some troubleshooting to verify wiring was all good - it was). I cold see the clutch ATTEMPT to engage (the gap between the clutch plate and the pully got slightly smaller) but the clutch plate wouldn't spin. I knew my compressor was not seized. I removed the clutch plate and discovered the pullyside clutch mating surface was deeply gouged in a pattern that matched the clutchside mating surface. With a dremel I was able to grind the circular ridges flat and basically make the pulleyside mating surface flush/flat again. I would have preferred to take the pulley itself to a machine shop and have it "decked", but found the dremel did a good enough job of it. After reassembling everything, minus the airgap shim, it worked perfectly.
A link to my (albeit sparse) thread: http://gmtnation.com/f23/yet-another-c-thread-clutch-seriously-worn-3906/.

My fix was in June of 2012 and I haven't had one problem with it since. And I had MANY days in the 90+ range. With 130,000 or so miles on this thing, I'm not about to soak $1000 into the A/C if I don't have to. The simplest (cheapest) fix that works, for me, is what I go with - but to each their own.

I saw you ordered a clutch but haven't installed it yet. I would do that before anything else - if that fails to solve the problem, then maybe a compressor - but my money is on the clutch.

I agree, but not necessarily linked to excessive "air gap". Usually linked to weak field coil not having enough electromagnetic "pull" to capture the plate and engage compressor 100%. Reducing "airgap" by removing he shim will partially compensate for the weak coil for th short term. As ambient temperatures go up the clutch field coil overheats and capture strength weakens. This is why there is a failure at temps over 85 degrees.....please see post #3.
 
Dec 5, 2011
570
Central Pennsylvania
c good said:
I agree, but not necessarily linked to excessive "air gap". Usually linked to weak field coil not having enough electromagnetic "pull" to capture the plate and engage compressor 100%. Reducing "airgap" by removing he shim will partially compensate for the weak coil for th short term. As ambient temperatures go up the clutch field coil overheats and capture strength weakens. This is why there is a failure at temps over 85 degrees.....please see post #3.

Coil failure is usually evidenced by an increase in coil resistance (even if only at high temps). I don't remember the readings but I remember my coil was in spec for ohms even at high temps. The air gap setting has to do with the distance the clutch leaves have to flex to make contact. The greater the distance the harder it is to flex. That's why air gap is critical - too large a gap and the coil can't flex the clutch enough - too small a gap and it can make unwanted contact. After I ground my pulley and removed the shim I found the air gap was in spec - voila, clutch works.

I "get" what you're saying though, and the OP will be we'll served eliminating things by diagnosis. I was just ready to wrench sooner than he was with my problem. If his is a weak clutch at least he already has a replacement available.
 

meerschm

Original poster
Member
Aug 26, 2012
1,079
I did break out the feeler gauges, and it looks like .015 gap in the clutch.

( It looks like the clutch moves more than that, but that is what I could insert)
 

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