Strange A/C issue

[kkeo211]

Just an update. It’s been about 7 days since the envoy was in the shop and the AC system was vacuum filled and the AC system is still working great. I really expected it to be back in the shop in 3 to 4 days given the amount of leaking I was seeing prior to it being in the shop.

Could vacuum filling the AC system could have removed moisture or other contaminants from the system that was causing it to act up?

I’m keeping my fingers crossed. There may be only about another 3 weeks of warm weather (mid to low 80’s) so if I don’t see an issue/get it fixed by October, I may not know if there is an issue until April.

 

[Mooseman]

I doubt that the vacuum filling played a role but the amount that you use it may. With cooler weather, you are probably using it less. If you have a leak on the high pressure side, it would leak faster when running. With the vacuum, they should have been able to see if there was a leak if they left it under vacuum for 30 minutes and see if it stayed the same.

The only other explanation I can see is that one of the connection ports has a dodgy valve seal and hooking it up to the gauges somehow resealed it.

Hope it works out.

 

[kkeo211]

The shop said they could not find the leak so that's why they put dye into the AC system and told me to drive the Envoy around until the AC stopped working. I pickedup a black light from Amazon the other day and tried to find the leak. I spent a good ten minutes looking aroudn but coudn't see any dye coming from any of the AC components.

I hope what ever the issue is, it's an easy fix.

 

[kkeo211]

Just wanted to give an update on my A/C issue. Its been about 6 month since the show vacummed filled my HVAC system.

It finally got hot enough in Richmond to test the AC out. Yesterday, we drove for about 20 minutes and the A/C was cold and worked great. If there were a leak, would the system only leak refrigerent while using the A/C system or would it leak anytime? I'll continue to test as it gets hotter.

 

[Mooseman]

If it has a leak, it will always leak. It might go faster if it's on the high side and you turn it on but it will be too low or empty by then.

 

[kkeo211]

Mooseman, thanks for the info. I was not sure what needed to happen for refrigerant to leak out. As far as I can tell, the A/C system works well and have not had any issue. The shop I took it to said they put die in it. I took a blacklight and can't see any indication that a leak is happening. I've replaced the low pressure switch and compressor relay already so at this point I'm sort of at a lost on what to try next.

If the A/C stops working again, I'll have to take it back to the shop.

 

[MAY03LT]

Could also have been a sticking service port schrader valve that would stick open and slowly discharge the system. I've had a couple GMs do that exact thing.

 

[kkeo211]

Update: Took the Envoy out for a ride and the AC did not work. The compressor engaged but no cold air. I'll have to get my gauges out again to test the pressure and fill if needed.

The Envoy is an extra vehicle so I'm not to worried about getting it fixed soon. I use it for fishing and hunting so AC doesn't really matter in the fall, but it will suck when fishing in the summer.

 

[Mooseman]

If the compressor is running and the receiver is cold, could be an HVAC actuator issue.

 

[kkeo211]

I finally got a chance to put on the gauges today. It was about 77 outside, humidity was high.

For the performance test (engine one, AC highest setting and verified the compresses engages). The readings were:

Low side about 37 PSI
High side about 150

According to the service manual, the readings should be

Low side 31- 44 PSI
High side 160 - 200 PSI

It looks like I'm in range for the low side and just slightly out of range for the high side. Do you guys think this is enough to cause the AC to act strange? The air coming from the vents felt cool but not ice cold like normal.

 

[Texan]

Feel the accumulator (passenger side @ fire wall).
Should be cold, sweating if high humidity.
Probably low on Freon.

 

[mrrsm]

EDIT:

Here is a more comprehensive Tech Article I wrote back in 2010 on another forum where I am known as "60dgrzbelow0" with a 13 part "Baker's Dozen How To Repair Automotive A/C"

http://gmtnation.com/forums/threads/how-to-repair-your-air-conditioning.14558/

Your original post hints that the vehicle was in the shop for the a/c repair. Here are the normal orders of operation for these general repairs:

(1) Recover the R-134A Refrigerant as per EPA-608 EPA-609 Clean Air Act Regulations
(2) Remove the bad components such as a seized compressor & REPLACE SCHRADER VALVE(S)
(3) Replace the Orifice or TXV liquid line metering device and Accumulator
(4) Flush the system high and low lines, evaporator and condenser
(5) Pre-fill the new compressor, new accumulator and condenser each with 2 Oz of PAG Oil
(6) Replace all O rings and rotate compressor 10 Xs B4 installation
(7) Flush the system with Dry Nitrogen and pull a vacuum down to 25 microns
(8) With the Engine off, Pre-fill on the Low Side Service port with 1 can of R-134A
(9) Start the vehicle with the A/C on & Blower set to high
(10) Continue filling the system with vapor on low side until low pressure switch engages compressor
(11) Install Manifold Gauge Set and sample local ambient air temperature
(12) Insert a Digital Probe Thermometer into the air vent inside the SUV
(14) Use a Temperature-Pressure chart to determine how much additional refrigerant to add
(15) Normally ...refrigerants get weighed into the system at the factory...use the Guages
(16) Take at least 10 Minutes to wait for the system to normalize and check the thermometer
(17) A good indication of proper functioning is when condensation settles on Accumulator
(18) Try not to over fill the system...make frequent checks for interior temps

If the system leaks have not been taken care of B4 hand....pulling a vacuum will draw in damp ambient air and non-condensible gases that will cause the moisture to freeze in the low side capillary expansion evaporator tubes and block the flow of the refrigerant. The only way to to know for certain is to use a two stage scroll vacuum pump with fresh vacuum pump oil fitted with a Digital Micron Gauge. Once the system is vacuumed down... The pump is turned off using ball valves and the Micron Guage is observed for any rise in internal pressure. If the internal system pressure rises ...say above 300 Microns in 30 minutes... There is a leak somewhere that must be fixed first...and then another vacuuming must be performed. No matter how new the components are...if ambient air is being pulled into the system....it will have moisture that can completely saturate the PAG oil and Silica Gel pack inside the accumulator ...and the residual water will eventually freeze somewhere inside the expansion-evaporation side of the the A/C system and fail to cool.

If your condensing coils are too dirty....the sub cooling necessary to change the low side refrigerant vapor into a liquid on the high pressure side will not occur with enough heat dissipation to allow the liquid to form...and cause a problem upstream where the liquid must expand through the Orifice and flash into a vapor drawing heat from inside the cabin into the evaporator coils as superheat to be removed by the condenser near the radiator.

 

[kkeo211]

MRRSM,

Thanks for the detailed write up. Unfortunate, that is way over my head when it comes to HVAC knowledge and experience. I think I will just drop it off again at the shop and see what they can find. The Envoy is my extra vehicle so I'm not to worried about this issue. If it were just a little low on refrigerant, I may decide to get it fixed right away. If it is a major leak I will probably just go old school and deal with no AC.

 

[mrrsm]

For those who will attempt to repair and re-seal A/C Leaks that are indescribably difficult to locate on fully installed Automotive HVAC Systems... I would recommend using NYLOG on ALL of your SHRADER VALVES, "O" Rings and Flare Connections and Fittings. You can find the small bottle of this stuff (RED) Flavour for Auto A/C...at Amazon for around $10.00...Very inexpensive insurance for the prevention of Refrigerant Loss and Leaking Fittings that normally plague and aggravate us all eventually!

http://www.amazon.com/Refrigeration-Technologies-RT200R-Nylog-Sealant/dp/B008HOSQ3E?SubscriptionId=AKIAILSHYYTFIVPWUY6Q&tag=duckduckgo-d-20&linkCode=xm2&camp=2025&creative=165953&creativeASIN=B008HOSQ3E