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Tahoe AC mystery

jmtrup on Sun May 16, 2010 12:01 AM User is offline

Year: 2001
Make: Chevy
Model: Tahoe
Engine Size: 5.3L
Refrigerant Type: 134

I would like some ‘second opinions’ to this diagnosis since the cost is approaching 10 bills.

Both the front and rear AC’s on my 2001 Tahoe work flawlessly for regular driving around town. However, I make a lot long drives and have a problem that only surfaces 2+ hours into a trip. About this time, the front AC starts blowing warm air while the rear AC keeps blowing cold air. This Tahoe has ‘auto’ air so the blower will speed up and blow the warm air trying to keep the car cool. If I turn off the front AC (and let the rear AC cool the car) I can usually turn it back on 45-60 minutes later and it will work for several more hours. If I were to pull off the highway for a stop while it is doing this, I have noticed that no condensate is dripping from the front evaporator. However, 15-20 minutes after stopping, condensate will start dripping at 3 times the normal rate.

Since the repair shop can’t easily duplicate the problem, they can only diagnose based on how it normally performs – and they say it works just fine, pressures are right and Freon levels are perfect. They seem to have a shotgun approach for the repair and want to replace the fixed orifice tube, low pressure cut out switch, drier/accumulator, TXV, and do a system flush. Then we need to wait a month for my next trip and see if it is fixed.

Any thoughts? Thanks for your help.

newton5 on Sun May 16, 2010 2:50 AM User is offlineView users profile

It sounds like your Low Pressure Cutout Switch (or Cycling Switch) has gone out of range and your evaporator is freezing up due to normal condensation .
The front AC system on your Tahoe is a Cycling Clutch system that relies on that switch to turn the compressor off at times to prevent the evaporator from freezing into a block of ice.

The switch is located on the Accumulator (The "AC Can" near the right side firewall).
I don't see the switch listed by the Forum sponsor, but they can certainly get it for you. It should also be in stock at your local auto parts store for about $12-15.

jmtrup on Mon May 17, 2010 8:34 AM User is offline

Since this was the least expensive thing the repair guy suggested, it's worth a try.

Although I have rebuilt several cars in the last 30 years, the AC is something I have not had to mess with - so please excuse my ignorance. Can the switch be replaced on a charged system or do I need to have it evacuated and recharged upon completion?

Edited: Mon May 17, 2010 at 8:39 AM by jmtrup

GM Tech on Mon May 17, 2010 11:13 AM User is offline

You can simply unscrew it- it has a schrader valve in behind it that will keep your refrigerant from escaping- be careful- you are dealing with a plastic base- to not tighten new switch any tighter than snug- I've seen them be cracked before from over torquing-- they seal on the ID, so more torque does not mean more sealing....

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

jmtrup on Tue June 22, 2010 1:49 PM User is offline

I replaced the switch and took a long trip and everything seemed to be working fine. HOWEVER, before I took the trip, it also developed a noise around the compressor. The shop mistakenly diagnosed it as the AC tensioner, but then determined it was the compressor. Since I didn't have time to fix before my trip, I drove about 1400 miles in two days with the AC working great. Then I lost all cooling about 200 miles from home. The compressor still turns, and has quieted down a little, but will not cool. There also appears to be a very small film of melted plastic between the compressor and the pulley. Since my Dallas Chevy dealer is just as competitive as the independent shops on the replacement, I will likely take it to them tomorrow to replace the compressor and determine what else may need replacing.

Any last minute advice or warnings?

Edited: Tue June 22, 2010 at 1:59 PM by jmtrup

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