I know for most people AC is not an issue this time of the year. Even here in southeast TX, it's not either, but hot weather is fast approaching, and I'm trying to get a fix for a problem that occurred last summer.

I'm a relatively new owner of a 94 ZR-1 and I'm having problems with the AC not cooling only after the car has been re-started. Based on the experience I had all last year, the AC works fine, cools great, after the car is started for the first time. But if I make a short trip, turn off the engine for even only a few minutes, when I re-start the car to get back on the road the AC runs fine...at least the fan runs and and blows air...but the air is not cold, not even cool air.

I have have tried manually turning off the AC before I park the car and then turn it back on when I re-start the car, but that has not effect. I have not tried to determine what the minimum time, (in hours), is before the AC will begin blowing cool air again. The only thing I can say for sure is that after I start the car up for the first time the next day, the AC works perfectly.

Several years ago I had a 92 (LT1) non ZR-1, for a very short time and it exhibited the same AC problems. Any one have any similiar experiences, along with any ideas/suggestions about how to fix it?

 

Hate to ask an obvious question, but have you checked the pressure/gas in the A/C. I have a very slow leak and do a fill once or twice a year.

 

My guess is that you have a bad high pressure switch that activates at too low of a pressure or you have too much freon in the system and actually have too much pressure. As freon heats up it expands and creates more pressure in the system. When you run the car and get the engine hot, and then turn off the car, the heat from the engine heats up the AC system causing the pressure in the system to go up, possibly activating the high pressure safery switch. Check your freon pressure when the car is hot.

Does the compressor cycle at all, and when does it cycle? This answer could also be used to help trouble shoot your problem.

 

There isn't a High Pressure Switch per se; '90 and up use a Pressure Sensor which returns a voltage signal to the PCM that is proportional to pressure. It's used for Fan Control, Clutch engagement, and in place of the High Pressure Switch. Some GM's have a troublecode for this Sensor which will often be in the BCM, though some PCM's will flash it - see if there's any code in the 70's. Otherwise, you need to scan to see what this signal shows and that will also give you Static Pressure (a/c off) and the High Side (a/c running) which is useful if you don't have access to a Manifold Gage Set. PCM monitors the Sensor for a voltage (pressure) increase when the Relay engages the clutch. If it doesn't increase, power is removed from the Relay. First things first though, is the compressor engaging? Is an LED flashing on the Control Panel?