Automotive Air Conditioning Information Forum (Archives)

TomBaumann on Fri April 22, 2011 7:24 PM

Year: 2006
Make: Chevy
Model: Tahoe
Engine Size: 4.3
Country of Origin: United States

I am troubleshooting a 2006 Chevy Tahoe with 60k miles on it. When I turn the AC on, it blows outside temp air (not cold) and the compressor does not turn on. When I turn the climate control to heater it gets much hotter so the acutators are working.


I have look thru these forums and taken the following steps to troubleshoot:

- Topped off /checked the pressure in the ac system with a can of coolant with a pressure gauge - NORMAL

- Bypassed / jumpered the low pressure circuit/swith just under the hood very close to where coolant would be added - COMPRESSOR DID NOT TURN ON

- Ran a wire from the car battery directly to the connector on the side of the compressor - CLUTCH/COMPRESSOR RUNS, BUT AIR IS STILL HOT - ONLY RAN IT THIS WAY FOR 90 SEC OR SO

I am neither an auto mechanic nor an A/C mechanic, but I have done lots of auto repairs.


A couple of factors that may or may not be relevant:

The car sat for aprox 2 years without being run. I would start it every month or two, but not turn on the AC.

The left vent cover broke, and my kids managed to throw a couple of small pencil shaped toys down the vent shaft.

Any help would be greatly appreciated!

GM Tech on Fri April 22, 2011 8:59 PM

I would contend that that "normal" (green zone) on your pressure gage from your "death kit" means normal for when the a/c is running (compressor is on). Your compressor is not on..therefore, the pressure is NOT normal--- now let's talk real pressures.....it takes 47+ psi to activate your cycling switch- which you said you jumped, but I'm not sure from here you have the correct wiring harness- (it should be the one connected to the low pressure cycling switch on the accumulator)

System static pressure needs to be 47+ - is yours at least that high (at 70+ degf ambient)? If not you have lost nearly 95% of your refrigerant (at 70+ degf ambient)- due to a leak.

Also, I have seen those goofy control heads - un suburban mostly that show an a/c "snowflake" but if you look real close, there is a line through that snowflake - so if this button is pushed, it means NO a/c. Normal control heads have a button to push that ENABLES a/c-- these goofy control heads have a button you push to DISABLE the a/c.

To run the a/c - and have the control head send the proper ground signal to the a/c relay- the "auto" button must be pushed.

The fact that the compressor ran when jumpered out (would have much easier to do it in the underhood relay center with a paperclip BTW)- and the lines and air were NOT cold, only confirms a massive loss of refrigerant.....so two strikes against you saying the system has a massive leak. Do you have rear air?

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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......

Edited: Fri April 22, 2011 at 9:03 PM by GM Tech

TomBaumann on Sat April 23, 2011 2:00 AM

I really appreciate the reply... I will recheck the refrigerant levels and report back.

iceman2555 on Sat April 23, 2011 3:15 AM

There is only one method to determine refrigerant charge.....recover and measure/weigh the amount recovered. Then evacuate the system for app. 15-20 minutes and recharge to OE specifications utilizing the correct recharge equipment. A can of refrigerant and a hose with a $.25 gauge is not going to accomplish this. Service the system correctly....keep screwing around with jumping this and jumping that....and operating the system with a undercharge and a good bet is that you will be spending some serious cash on new parts.....heck, this will occur if the system is not totally recharged.....undercharge this system several ounces and the compressor will suffer serious damage due to lack of lubricant movement.
Static pressures are not an indication of the amount of refrigerant within the system. At any given temperature a 12 oz can has the same pressure as a 30 lb cylinder. It is a temperature/pressure thing...
Adding one can or a parcel charge of one can should be sufficient to activate the compressor...unless there is a problem in the electrical supply to the coil. Be careful attaching 12 volts directly to the compressor....some of these Denso units have a built in diode in the coil and may be damaged.

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Thomas Jefferson