I have an 88 with the electronic climate control and I have a problem with the A/C. When I first start the car with a cool engine, the A/C works just fine but as soon as the car warms up the cool air stops and it starts blowing warm air. The clutch kicks in fine at any temperature so I think it must be charged. Any idea what gives?

 

My car just started doing the same thing, I have found that if I restart the car it cools again and usually continue to work. I think the problem is the climate control computer but have not had a chance to run the diognosis on it yet.

 

Does the compressor cycle (turn on and off) more than 8 times per minute once up to temp? Is there any ice on the lines? If no to the above, remove the Blower Module which is on the left side of the Evaporator Case and look inside. You should see a door and as someone operates the Controls between 60 and 90, that door should move. If it doesn't, the electric motor that controls it is connected to the door linkage with a plastic clip and that clip likes to break. If it has, it'll flop around and give you hot/cold, cold/hot, etc, etc. Access the motor and the linkage by removing the passenger side hush panel. Taking the ECM out helps you see everything too.

 

http://members.shaw.ca/dankai/AC%20Electronic.pdf

 

Did a little more checking and it turns out that the problem is pretty predictable. When the engine is cold, the A/C works fine. As soon as it heats up to the 160 - 175 degree range is switches from solid cold to hot air. Doesn't sound like the door is flopping around, but rather switching at a certain point. Any more ideas?

 

I have the same problem with my 94, the A/C compressor seems to switch on/off every time I mess with the A/C switches, or restart the engine!

freon level is ok, dont know how to fix this ?

 

If it's cycling - turning on and off - that's usually indicative of a low charge or a plugged up system. Whatever liquid gets into the evaporator boils off immediately and by the time anything gets to the low pressure switch, there's no oomph left to it and the contacts open cutting power to the compressor. (For R12, the contacts open at 25 psi; R134, 22.5 psi). The '90 and above also monitor that switch as well as the high pressure sensor for an increase in voltage/pressure when the compressor engages. Cycle too rapidly or if there isn't a couple of point rise in the voltage signal from the pressure sensor ('90 and up), the system shuts down until you fix it. If you have a '90 or above and it hasn't done that (stopped working altogether), another possiblity would be an intermittent connection at the low pressure switch. You might just try holding the connector on the switch to see if the cycling goes away. Otherwise, you need to see what the pressures are. A scan will show you the high side or signal from the pressure sensor ('90 and up). Better to hook up a manifold gage set.

Pressure rises with temperature, so the the higher the temp at the condensor, the higher the pressure of the liquid getting metered into the Evaporator and the pressure the liquid boils at, determines the temp of the air out of the vents. The higher the outside temp, the higher your vent temp, though even at 100, most should still blow out some high 50, maybe 60 degree air.

Realistically, cycling, once warmed up, shouldn't happen with outside temps of 70 or above - as long as everything can get through the screen restriction or orifice. If it is cycling or shutting down with high temps, that could be an indication that the liquid is being held back and with that, the high side goes even higher. Fortunately, the high pressure sensor or switch will signal the ECM to cut the relay (or break the circuit - depends on Year) at 400 psi. That way, it doesn't blow apart and put a hole in the hood. If you're confident that everything else is working, best to check it with some gages and then post your pressures and the outside air temp for more help. Otherwise, the Vette a/c system keeps the clutch engaged as long as the low pressure switch doesn't drop below 22.5 to 25 psi and the high side is less than 400 psi.