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Old 05-28-2013, 07:39 PM   #1
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Join Date: Nov 1998
Location: Louisville, KY
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AC problem?

It's finally starting to warm up around here. I turned the AC on today, and nothing but warm air came out. I tried it about three weeks ago, and it worked. I don't think the compressor is coming on, as I don't hear the "click" I usually hear when it comes on. There are no strange noises from the compressor. I seem to remember the relay can be removed, and a jumper used to check to see if the compressor will come on. Which pins do I jumper, and I'll listen to any other suggestions about checking the AC.
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Old 05-29-2013, 12:21 AM   #2
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Location: Kernersville, NC
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Re: AC problem?

If your AC system has lost it's charge, then the pressure sensor in the system will prevent the compressor from coming on. It's to protect the compressor, so don't try to bypass it if your system pressures are not correct.

There could be other reasons like a bad relay or a few other things. I know it can hurt the wallet, but I'd leave the AC troubleshooting to the certified techs. I recently had to have my low pressure schrader valve replaced because it was leaking. I had the good folks at Flow Chevy do the work. Approx $200 to discharge the system, replace the valve, and recharge the system.

The only thing that kept most of the charge in the system is that plastic cap on the port. There is a seal in there that is a last resort to keeping the system charged in case the valve leaks.
Eric R.- Electrical Engineer - ODU
1996 Blue Z28, 6M
CC503, 1.6 Pro Mags, Kooks, Stock heads, K&N CAI.
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Old 05-29-2013, 12:56 PM   #3
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Re: AC problem?

As ace says, running compressor w/o refrigerant can destroy it. PCM will not pick relay if the sensor is reading below 22 lbs. Here is the schematic ref shbox.com http://shbox.com/1/hvac_compressor_control.jpg . You can pull relay and with ignition on and engine off jump B1 to B4 you should hear the clutch click. If engine is running only do it momentarily enough to see if clutch plate engages and compressor moves w/o squealing. Since you say you can't hear clutch click, most likely you lost the 22 lb cut off threshold, no need to run the engine. If clutch activates w/jumper , next step would be to get a 134 can w/a cheap gauge attached and verify pressure w/engine off. If below 22 lbs start adding.. At current warmer temps above 70* F one 12oz can of 134 on and empty non running engine system should give the system at least 22 lbs enough for the compressor to start sucking when engine is turned on. ALSO when you jump the clutch it will most likely throw an AC DTC (w/o SES indicator). That prevents the PCM from picking the clutch until the PCM is reset. It can confuse the heck out of you after you add 134 and it still does not run...Good practice is to reset PCM BEFORE trouble shooting to eliminate any old AC codes preventing clutch pick and AFTER trouble shooting to clear any DTC's you created. Also some try jumping the pressure sensor --DON'T -- the pressure sensor is a 0-5v sensor feeding the PCM not a switch, jumping it will throw an AC DTC in the PCM and prevent subsequent AC activation, again causing confusion after a fix and requiring a PCM reset.
I'm Bob.. 1994 Z28, A4, Stall, CAI, Cam, RR's, 342 rear, LT's , CatBack, Tuned

Last edited by bobdec; 05-29-2013 at 01:16 PM.
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Old 05-29-2013, 12:56 PM
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