Any GM air conditioner experts out there?

[Professor]

Any GM air conditioner experts out there?

99 GMC Sierra 2500 (99-2006 BODY STYLE)
AC works and then stops blowing cold air. Compressor is cycling off.

1) You can turn of the AC and continue to drive a few miles and then turn it back on it will start working. Turning it on immediately will not.

2) Another 3-10 minutes it will stop again.
Air flow seems to slow down slightly. Running the blower at the highest level will make it run longer.

3) Higher humidity seems to make it last less.

4) Outside air lasts less than recirculation mode.

5) Split between air intake and discharge is usually 40 degrees or more.

6) Driving a constant speed 95 degree ambient air outside I can easily see low 40s on at the discharge.

7) Cabin air filters have been changed.

8) System has been checked once (was told it was a couple ounces low). Took it back as it was doing the exact same thing when I left. They discharged the system, pulled vacuum , and recharged. Still the same.

I think the evaporator is freezing up but why? Low refrigerant and they missed it twice?
I may have to dig out my gauges and take a look at the pressures.

Anyone have any ideas?

 

[rubber2burn]

Rick does it stop all together or does it move to the Defroster?

 

[Professor]

Rick does it stop all together or does it move to the Defroster?

no, it remains coming out of the primary vents (or whatever is selected), it just seems the amount of air drops a bit.... maybe 10-20%. It may just feel that way because of the temp rise.

The compressor does not kick back in until it the ac button is turned off for a while and back on.

Almost like the low pressure switch dropping out on the older r12 systems for low freon but it never cycles back on.

 

[SHADiGUY1]

replace hi and  low pressure switches man..they still have them on the r134 system very common problem im a mechanic and come acrossed this quote frequently actually. Either that or could be a clogged orfice tube.

one way to check if its the pressure switch is there is a little plug run a jumper acrossed it if compresser comes on and stas on its one of your hi or low pressure switches.

 

[Supergank1]

replace hi and  low pressure switches man..they still have them on the r134 system very common problem im a mechanic and come acrossed this quote frequently actually. Either that or could be a clogged orfice tube.

one way to check if its the pressure switch is there is a little plug  run a jumper acrossed it if compresser comes on and stas on its one of your hi or low pressure switches.

+1 on that orifice tube, they get clogged easy. that low pressure switch should be on the accumulator(another thing that goe`s on GM`s) or low pressure line .

 

[Red05]

It does sound like a clogged orifice screen, but that could be a sign of a compressor on the way out. Checking the pressures and what they do as the system begins to malfunction will tell you a lot.

 

[In10SS]

orifice tube screen clogged is my first guess too.

 

[BusaWizard]

Put A/C gauges on system, if orifice tube is clogged the low side will draw into a vacuum, also is the drain hole for the evaporator open and draining? I've seen these clogged and freezing the evap. Check coolant level, are cooling fans working properly? Does the condensor have any debris in it? Try blowing it and the radiator out. You can take it to the car wash and pressure wash it.

 

[Spudley]

Excellent coverage guys !!!

If you ended up with one of the "screwie" production compressors with the teflon vanes, you're screwed. Microfilter / Orifice is clogging, and compressor is failing. It goes off, the particulate relaxes, and it acts as if it's clearing, then re-clogs. Check pressure switches, via bridging, and if that yields no results vacuum down, pull Orifice screen and check for small black gunk. If found, pull compressor, condensor, and flush anything in between thoroughly including evaporator. Replace compressor, condensor, orifice filter, and receiver / dryer.....been through this a couple times....

If you go the latter, do your homework and stay away from the teflon-vaned compressors in the future....

 

[SHADiGUY1]

i am good for something lol... let me know how it works out,

 

[johnnycrash]

My 2004 GMC 1500 Sierra does something similar. You're going down the road and the cold air is blasting, then all of a sudden the air goes very hot. I mean REAL hot like not only has the compressor stopped but like the heater is on. What works for mine is simply turning the key off for about 30 seconds and then restarting (PITA if you're on the highway).

Mine is the SLT version with the auto climate control if that matters - and I have two friends with similar trucks that do the same thing. Seems to be worse on super hot days when you really have the AC on max.