Diagnosing AC 84-89

This covers all the wonderful things one can and sometimes has to do to keep cool air coming out of the dash:)

First we’ll cover the dreaded “A/C works fine till I stop”. This is a normal problem that effects most 84 and newer vettes. The a/c will cool perfectly till you come to a spot and then it blows hot air. What happens is a small switch located in the lowside line goes bad. This pressure switch causes the cooling fan to cut on when the a/c is used. When the switch goes bad the cooling fan won’t come on except for when the motor gets hot enough. As long as the car is moving there is enough air passing over the a/c’s radiator to allow it work. When the car comes to a stop no air is passing over the a/c’s radiator. I.E. it blows hot air. The fix is actually very easy and anyone can do it. The switch has a shrader valve under it so the freon doesn’t escape while the switch is being changed. The switch cost me around $16.00. I had to get it from the dealership. None of the parts places carried the switch. To test to see if this is the problem, wait till the car is cold. Usually 130 to 160 degrees. That way the temp of the motor wont cause the cool fans to come on. Now crank the car and turn on the a/c. The cooling fan should come on within 30 seconds. If it does not then this will cure your problem. If it does then the switch isn’t bad. Another test if to unplug the switch. As soon as the switch is unplugged the fan should come on. Also this is a cheap fix, while your waiting for the new switch to arrive:) Just leave the plug off the switch and the cooling fan will run all the time, as long as the engine is running.



This shows the general area of the switch.



Here we can see 2 switches the small one is the fan switch and the large one is the low side cutoff for the a/c to cycle.



The one I’m pointing to is the one to change. Remove the plastic plug from the switch and unscrew it counter clockwise. I.E. turn it to the left:) Try to do this fairly fast to let as little of the freon out as possible. The simple screw the new switch in place and again do it fairly quickly. The switch doesn’t have to be TORQUED down so don’t get carried away. Shrader valves don’t like to be tightened onto hard:)  Then plug the harness back onto the switch. Now crank the car and turn on the a/c. The cooling fan should come on within 20 seconds of the a/c coming on. If it does then all is well.

The Nest – All things crowz….