Strange A/C issue

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kkeo211

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My wife told me today that her Envoy has been having strange A/C issues. She says, sometimes the A/C goes from being cold, to sorta of cold (not warm or hot) and sometimes goes back to cold on the same trip. Today, she was on the highway (55 mph) and the A/C when from cold to sorta cold but never went to cold again. Then in another trip today, in normal city traffic it went from cold, to sorta cold, back to cold. Reading other post on A/C issues, it seems like I should look at the following things.

1. A/C low pressur switch
2. Fan Clutch
3. A/C low and high pressure.


For #1, I have read that the A/C low pressure switch can go bad, but would it go bad everyone once in a while as described in the condion above? In other A/C post, it seems to either not work at all or cycle the A/C on and off.

For #2, I have noticed a low ticking sound for a while when the Envoy is first started. The fan blows like crazy for about half a mile then all seems normal. This is my first guess as to what may be causing the issue.

For # 3, I don't have any tools to messure the low and high pressure so I'm not sure if I would be worth it to just take it somewhere or by guages to see if pressure is low, and if it is, wouldn't that just mean that I need to take it to an A/C shop anyway because it may have a leak?

Any help would be great? Thanks!
 
Check Harbor Freight for a sale on A/C gauges. Around $50-$60 I think.
Is your CEL on? Any codes set? May just be a little low on Freon. Because it is not
a true sealed system (has rubber hoses) and O ring connections, it can loose a small
amount of Freon over the years.

Edit: you can add Freon with the gauge set, and proper directions.
 
Hi Texan, thanks for the quick update. There are to CEL or Codes thrown. It's strange, I was thinking about the low freon but wouldn't that just make the air not as cold all the time? I have a Harbro Fright near by that I can buy the gauages from but I'm not sure if that would help me out any, as I know nothing about A/C stuff.

So can I use the gauge on one of those freon refill kits to see if the pressur is low? and if it is, just fill it up with more Freon?

Thanks!
 
Look for other threads on the A/C system. To answer your question about one of those kits, not the best way
to check the system. You need to know both low and high pressures when operating the AC. There is a aluminum
vessel near the firewall on the passenger side (under the hood) known as the accumulator. It holds a level of
liquid Freon which bleed through a orifice into the evaporator as a cold gas. If the level gets to low, the system
will not cool. If you place your hand on this vessel and it is working, it will be cold to the touch. Years ago there
was a sight glass that you could look at for gas bubbles, but they are long gone for various reasons. From the
comment in you first post, it sounds like it may be the level of liquid Freon, but that is pure speculation.
 
Also check the temp of the passenger vents compared to the drivers side vents when set to cold if you have separate L&R controls.

I had my drivers side temp actuator go bad and wouldn't block all the heat when set to full cold.
 
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Thanks for the advice guys. I may go ahead and get those gauges from HF because I can use them for my other cars.

gmcman, I'll ask my wife to check both sides when this happens again. Its very strange, because it only happens once or twice a week. I'll have to see if it tends to happen just on really hot days (it was 96 yesterday).

I'll make sure to post as I try to identify the issue.

Thanks,
 
Here is the post on the tools at HF:
http://gmtnation.com/forums/topic/11174-ac-tools-at-harbor-freight/?hl=tools

Also grab my manuals as they have a pretty extensive section on HVAC. The first one (HVAC.pdf) has a troubleshooting section and chart of the pressures you should be seeing according to temperature and humidity.

From your first description, I don't think it's the fan as you said that moving at speed the temperature fluctuates. Another question is, do you have a manual (with sliders temp settings) or automatic HVAC (with the knobs and digital readout)?
 
Mooseman, I have manual sliders for tmp settings. I'll download the manuals and try to figure this thing out in the following weeks. My wife says it doesn't happen often so she is not pushing to get it fixed ASAP.

Thanks for the help.
 
So I picked up the AC gauge set from Harbor Fright. It looks like I am way low on refrigerant. Here are my readings.

Temp is around 92

With engine and AC off: Low is 29 and High is 30.5
With engine on and AC at highest setting. Low is 5 and high is 56.

From what I can tell, with the engine and AC one, it should be more like

86F-95F Low Side 48-50 PSI High Side 200-240 PSI

I'm I right on this with the low refrigerant and I need to add more? It seems like it is really low.
 
You're right. But adding refrigerant without troubleshooting the leak is not a good long-term tactic. Like jumping your wife's sister - might satisfy a short-term need only. Just sayin'.

Note: My wife has FIVE sisters and I only have ONE brother, so I've resisted FIVE times the temptation she has. :wink:
 
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And I would stay away from sealers. They are snake oil that cause more problems than they fix.
 
So I think I have been reading the gauges wrong. My first attempt, I just read the numbers of the gauge for r134a, but didn't read the inner black numbers. I read the instructions on the gauge set but didn't see any description on how to read the gauge correctly.

I did take pics, can someone confirm? From the new readings at 92F, it reads 41 on the low side and 256 on the high side. According to the service manual, I'm a little low on the low side and a little high on the high side. Is that still within spec, or I'm I low on refrigerant, or I'm I still reading the gauges wrong?

Thanks!


ac_on.jpg


ac_on2.jpg
 
It appears to me that the low psi is 37 and the high psi is 205.
The outer scales are temperature in C. I hate the metric system.
Look at your post #9 for proper pressures. Probably less than
one 12 oz can low.

Edit: It would interesting to see the instructions.
 
So, is the correct way to read the gauges is to only read the inside pressure. I thought the correct way to read it was to read the the inside setting, then add the pressure reading for r134a. I read the entire instruction set, and it never explains how to read the gauge set.

Here is a link to the gauge set. The instructions that came with my set are slightly different.

http://manuals.harborfreight.com/manuals/92000-92999/92649.pdf
 
This is a complicated subject. I can not explain it simply. Those outside numbers are temperature values in C
for various types of Freon. Blue Green and Black. The red scale is pressure in bars. You should only be looking
at the Black inner scale PSI (pound per square inch). This scale also shows vacuum (negative pressure) in inches of
mercury (inHg). The instructions are rather light, but assume that you understand how the system functions. I would
suggest that you search for more information about basic refrigeration system operations.
 
I've never used those other numbers, just the straight PSI. Found this video which is pretty good.

http://www.youtube.com/watch?v=UW1GDiOa0kE


If you download my manuals, the HVAC section has charts for what pressures you should be seeing according to temperature and humidity and what vent temperature you should get.
 
Guys, thanks for all the help. It goes to show you that if you don't know what you are doing, "Ask". If I had just used what I thought was the correct readings, I would have either over/under charged my AC system.

Thanks for all of your help, I will let you guys know how things turn out. My plan is to charge it back up to normal levels, then see if there is a significant leak or maybe just a small leak over time. That will help me decide my timeframe for taking it to the shop.

Thanks!
 
Okay, so this issue has not gone away. About 2 weeks ago, I bought a 12 oz. can of r134 with no additives from Autozone and charged the system back up. For a while it seemed to have worked and pressure on the low and high side seemed within the guidelines.

Now, last week we took a trip to the beach, and during the 3 hour drive the AC started to get cool twice on us(as if the AC was not working, but the fan was blowing). I turned the AC off for about 10 minutes and when I turned it back on, it started working again. This happened once while going about 55mph and while again while stuck in standstill traffic. The temperature outside was about 85-90. It didn't happen again for the entire week at the beach.

When we got home, I checked the AC pressure again and here are the readings.
In my garage at 80 degrees with over 50% humidity,
Low is at 35 and High is at 200.

According to the service manual, this is within range
76-85 Low should be 31-44 and High should be 160-200.

What else could cause this issue? I was thinking about just replacing the low pressure switch just in case it is starting to go bad. Does anyone have the part number? Looking on rockauto and not sure which one it is. Not sure what else to check.

Any help would be appreciated.

Thanks,
 
I think you needed to check the pressure while it was flaking out. Your high pressure could have been TOO high, and the compressor shut off for high pressure. That's a sensor IIRC, not a switch you can change easily. Also, when it quit working, was the compressor not running and therefore the accumulator wasn't chilly? There have been multiple reports about compressor clutches failing to pull in due to weak magnets / excessive gap, that happens more when the under-hood temps are extremely hot.
 
The_Roadie said:
I think you needed to check the pressure while it was flaking out. Your high pressure could have been TOO high, and the compressor shut off for high pressure. That's a sensor IIRC, not a switch you can change easily. Also, when it quit working, was the compressor not running and therefore the accumulator wasn't chilly? There have been multiple reports about compressor clutches failing to pull in due to weak magnets / excessive gap, that happens more when the under-hood temps are extremely hot.
Click to expand...

Hi Roadie,

It’s been difficult to diagnose the problem. It happens so infrequently that when it does typically happen, my wife is driving the Envoy and I'm at work. The few times it has happen to me, I'm on the highway or by the time I get home, it starts to work again. When the AC stopped working while we were stuck in beach traffic I was thinking about popping the hood and seeing if the compressor clutch was catching but then traffic started moving again.

I'm hoping to catch it again when I have the Envoy. I'm going to just pack the gauges with me so I'll be prepared to diagnose it. At first I thought it might have been a bad fan clutch going but what is strange is that it happens while I'm going at highway speeds (good airflow and cooler engine compartment) or while at a stop (I would assume hotter engine compartement from no airflow).

BTW, I found the part number for the low pressure switch.
autozone cost part#MT0968 for $19.99.
 
The_Roadie said:
Have you changed the compressor relay just for fun?
Click to expand...
Other than charging the system, I have not done anything else. Should I go ahead and just change the relays and low pressure switch? I hate to throw parts and money at it, but they seem cheep enough.

Autozone Duralast Part Number: 19307 for $13.99.
 
About the only two choices there are is troubleshoot it, or shotgun it. Flaky intermittent issues often don't present themselves for structured troubleshooting. Only you know how deep your pockets are, and what your threshold of frustration is, to know if shotgunning is on the table. For me, if it's under $100 and troubleshooting might take more than a couple of hours, I consider shotgunning, but only changing one part at a time (if I can) so I end up knowing what the root cause ultimately was.
 
The_Roadie said:
About the only two choices there are is troubleshoot it, or shotgun it. Flaky intermittent issues often don't present themselves for structured troubleshooting. Only you know how deep your pockets are, and what your threshold of frustration is, to know if shotgunning is on the table. For me, if it's under $100 and troubleshooting might take more than a couple of hours, I consider shotgunning, but only changing one part at a time (if I can) so I end up knowing what the root cause ultimately was.
Click to expand...

Thanks for the response. I think I will buy the parts and swap them out one at a time. What should I swap first considering how the AC has failed? The parts are under $40 so it's not a big deal money wise.

I was going to take it to a shop but my thought was if the failure did not present itself while at the shop, the tech would be guessing just like I am.
 
Another thing you could try is clean the condenser, either with a regular hose or a pressure washer with a wide fan nozzle. Some have had poor performance due to clogging of the fins by bugs, dirt and sand.
 
This is a complicated subject. The level of the liquid Freon in the accumulator is critical,
and it moves up and down to a degree. That is why it is called a accumulator. You may
still be slightly low. If the system was completely empty, you would refill by weight.
In the meantime, I would change the low pressure switch and see what happens.
Next, if that does not solve the problem, I would a "little" more Freon.
 
If your high side and low side pressures are in the correct range while the compressor is running then you either have a bad low pressure cut out switch or a bad compressor field coil along with excessive "air gap". To eliminate the low pressure switch variable, when you notice the AC no longer cooling, stop and check the compressor. If the clutch is not engaging, jump the low pressure switch temporarily with a paper clip. Yes....a paper clip, un wound so the two ends can be put into the female end of the connector. If the compressor engages.....you have a faulty low pressure cut out switch. If it still doesn't engage, then you have a bad compressor field coil clutch assembly. Often this can be remedied by pulling a shim out from under the clutch assembly and closing down the "Air Gap". If the coil is failing altogether (which is often the case as it heats up) it does not have the strength to pull in the hub and engage the compressor 100% of the time while it is being "Called". At this point you have two options.....Put in a new compressor....or find a clutch/field coil assembly and install it. New compressor requires opening the system, new accumulator, orifice tube, evacuation, and recharge. Clutch coil hub replacement requires finding one in the first place (next to impossible) then pulling the old one off and installing the new one. This is a good option as it does not require "opening up" the system and thus saves the accumulator, emulsion tube, evacuation, and recharge step. HTH.....c good
 
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Everyone,

Thanks for all of the feedback and tips. My plan is to pick up a low pressure switch, and relay, replace them one at a time. I will also clean out the condenser. First I'll start with cleaning out the condenser then changing out the low pressure switch, if that does not work I'll swap out the relay. These parts are under $40 so I don't mind trying to solve this sporadic issue that way.

c good, thanks for all of the details. Part of the issue I have with resolving this problem is that in most cases, it happens while my wife has the car. The few times it has happened while I'm driving it, I'm either on the highway or by the time I get to a safe spot, the AC kicks back on.

I'll update as I try to resolve this issue.
 
The_Roadie said:
My wife would insist that I teach her to troubleshoot it under those circumstances. Or at least make some good observations. An option?
Click to expand...
I attempted to explain to my wife what to look for the next time it happens but she doesn't feel comfortable with trying to trouble shoot it. Her aversion to help me diagnose may change if the issue happens more often but as of right now, it is so infrequent that should would rather I trouble shoot off and on.
 
Update on my AC issue.

This weekend we were driving back home from the beach and about 45 minutes into the trip, the AC stopped working. When I arrived home, I pop the hood to see that the compressor clutch was not engaged. I turned the Envoy off and start to connect may AC gauges, when I start the Envoy back up and turn on the AC, I can see and hear the compressor clutch engaging for 5 seconds then turning off for 5 seconds (I observed this for about 30 seconds). After hooking up the gauges, I see that the pressure when the compressor is on goes down to about 25 psi, then goes to about 55 when it is off. This happens a bunch of times so I did a quick search online, and it looks like the AC system is low on refrigerant.

I went to autozone and picked up a bottle of r134 and start filling the system. As soon as I start filling it, the compressor kicks on and stays on. Thinking that I've solved the issue, I fill the system to about 43 PSI (its about 89 outside).

All is well until the next morning. I start the Envoy up and no AC, the compressor is not engaging. I take a shot in the dark and decide to drive to the parts store to pick up a low pressure switch and compressor relay. On the way there, about 10 minutes, the AC kicks on and works well. I decide to replace the low pressure switch and compressor relay anyway to see if one will fix the issue (they are only 35 bucks for both parts).

After replacing both parts, the AC system was still acting up. I put the gauges on and the low side is reading about 35 PSI, hmmmm (I filled it to 43 a day before, outside tmp is about the same).

Today, my wife says, it’s been working off and one sporadically. I'm going to hook the gauges up when I get home to see what the PSI readings are. If they are low, I may have a leak on my hands.

So for now, my assumption (guess) is that I may have a leak that is getting worst. But it is strange, that sometimes, after driving for a few mintues, the AC would start to work after warming up a bit. I've replaced both the low pressure switch and compressor relay. I don't think it is the "air gap" issue, because the compressor clutch does not engage when the engine is cold/warm sometimes.

Could a bad compressor cause this type of behavior?

Do I need to take my Envoy to an AC specialist? Or will most shops know what to do?

Thanks for any help on this.
 
You likely have a leak somewhere. I believe there is a dye by or recommended by GM for use in diagnosing leaks... or is the dye already in the refrigerant? Bah, I don't know as I've never had to deal with it, but look it up. Usually takes a UV lamp to spot the dye but it'll show where your leak is.

It's a sealed system, so refrigerant shouldn't magically disappear. It's just like an old fridge, as long as all the hoses and seals stay intact that same refrigerant charge can keep cooling for literally decades.
 
IllogicTC said:
You likely have a leak somewhere. I believe there is a dye by or recommended by GM for use in diagnosing leaks... or is the dye already in the refrigerant? Bah, I don't know as I've never had to deal with it, but look it up. Usually takes a UV lamp to spot the dye but it'll show where your leak is.

It's a sealed system, so refrigerant shouldn't magically disappear. It's just like an old fridge, as long as all the hoses and seals stay intact that same refrigerant charge can keep cooling for literally decades.
Click to expand...
I think you are right. When I got home, with the engine on and AC at full blast, I hooked up the gauges and saw that the low side was a little over 30 PSI and high side just under 200 with outside tmps around 90 or so. That is about a 4 PSI drop in a little over a day.

So when I revved the engine to about 1600 RPM, the strange compressor cutting on and off thing starting happening again. The pressure would go up and down from between 25 PSI compressor cutting off to 60 or so PSI to witch the compressor cut back on (about 5 seconds between cycling on and off).

So it seem with no engine load, the compressor would stay on at 30 PSI but with engine load, the compressor would cycle on and off. My guess is a leak somewhere causing low pressure on the low side that causing the low pressure switch cycle turn the compressor on and off.

I'm going to find a good shop to work on this. I'm not confident in my ability to find the leak and then fix it once it is found.
 
:iagree:
If you fill it one day and the next, it cycles on/off again, sounds like a leak. You should be able to buy a can of R134a with tracer dye in it but you will need a UV light to look for the leak (I've seen some as LED flashlights). Is your truck an extended 7 passenger? If so, that will add to the number of possible leak points with the rear system. It may also be leaking in a non-visible place, like inside the HVAC at the evaporator (like mine) so that would need a refrigerant gas leak detector, which is available at HF for $50. You could just go straight to the detector to find it.

Edit: you posted while I was typing :biggrin: . Good idea on taking it to a shop.
 
Dropped the Envoy off at the shop this afternoon. I'll update when I find out what the issue and cost are.
Crossing my fingers that it won't be much to fix.
 
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Picked up the Envoy from the shop yesterday. They said they couldn't find the AC leak and that I was almost out of refrigerant (so obviously, there is a leak somewhere). They "vacuumed filled" it? and have added dye in the system. They said to drive it around and when the AC stops working to bring it back and they won't charge for the follow up diagnosis.

I'm not experienced with AC issue, I guess this is sort of normal operating procedure right?

Thanks
 
Kinda. A good shop would have had a refrigerant gas leak detector. I have one I picked up at HF for $50 and helped me find my leak in my evaporator. They're hoping that the leak will be visible.
 
I was hoping they would just find a small leak that was easy to fix and take care of it. I just ordered a cheap UV flashlight on Amazon to see if I can find the dye/leak myself.
We will see what happens.
 
The "vacuum" part of a refill process involves putting a special vacuum pump on the system, pumping it down until there are only a few molecules of air inside, and leaving it like that for a few hours. It does two things - checks for leaks that let air INTO the system (if the vacuum doesn't hold with the pump turned off) and more importantly, it gets all moisture out of the system that typically gets into it when any part is exposed to outside air, as it would be if you change a compressor, hose, or any other part of the sealed system. Moisture will freeze and clog tiny orifices and kill the performance. That's why most DIYers aren't going to succeed working on their own AC systems. Without a bunch of special tools and a bunch of reading/youtubing.
 
The_Roadie said:
The "vacuum" part of a refill process involves putting a special vacuum pump on the system, pumping it down until there are only a few molecules of air inside, and leaving it like that for a few hours. It does two things - checks for leaks that let air INTO the system (if the vacuum doesn't hold with the pump turned off) and more importantly, it gets all moisture out of the system that typically gets into it when any part is exposed to outside air, as it would be if you change a compressor, hose, or any other part of the sealed system. Moisture will freeze and clog tiny orifices and kill the performance. That's why most DIYers aren't going to succeed working on their own AC systems. Without a bunch of special tools and a bunch of reading/youtubing.
Click to expand...
Thanks for explaining. I was not sure what the difference was, but it makes sense.
 
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