How to test AC Compressor
Burning Brakes
Joined: Nov 2005
Posts: 848
Likes: 1
From: 1992 LT1 6 speed Cayman Islands
1. Start engine.
2. Turn on AC while observing the compressor to see if the clutch energises and turns the compressor.
3. If compressor turns, Check the AC lines going from the compressor with your hand to see if it gets cold.
4. If line gets cold, check vents inside car to see if they are blowing cold air.
5. If all above checks out go for a drive and enjoy that AC. If not post where in the sequence there is a problem and the members here will walk you through a fix.
ONE FINAL NOTE.( or should that be first note)
Before doing the above, disconnect your negative battery cable for 3 minutes and reconnect it. This will reset the computer to send the signal to the compressor if it had shut down because of a code.
2. Turn on AC while observing the compressor to see if the clutch energises and turns the compressor.
3. If compressor turns, Check the AC lines going from the compressor with your hand to see if it gets cold.
4. If line gets cold, check vents inside car to see if they are blowing cold air.
5. If all above checks out go for a drive and enjoy that AC. If not post where in the sequence there is a problem and the members here will walk you through a fix.
ONE FINAL NOTE.( or should that be first note)
Before doing the above, disconnect your negative battery cable for 3 minutes and reconnect it. This will reset the computer to send the signal to the compressor if it had shut down because of a code.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
No codes before '90 so need to disconnect the battery.
Assuming the compressor engages, you want to feel the bigger line from the top of the Evaporator and the one at the bottom - JUST where it enters the Evaporator case. Touch that smaller, bottom line, anywhere else and you might burn your hand! Both lines should be cooler than ambient with the top maybe a bit cooler. If so, and the compressor engages, charge is at least close - something else is keeping cool air from getting to the vents.
Assuming the compressor engages, you want to feel the bigger line from the top of the Evaporator and the one at the bottom - JUST where it enters the Evaporator case. Touch that smaller, bottom line, anywhere else and you might burn your hand! Both lines should be cooler than ambient with the top maybe a bit cooler. If so, and the compressor engages, charge is at least close - something else is keeping cool air from getting to the vents.
Intermediate
Joined: Jul 2025
Posts: 30
Likes: 22
From: Central Indiana
I just pulled all the a/c stuff out of a box and installed it with all new green o-rings, accumulator, oil and 12 oz of 134A. The compressor clutch never engaged. I checked the fuse and made sure it is plugged in. How can I test?
Drifting
Joined: Nov 2018
Posts: 1,798
Likes: 579
From: Mays Landing, NJ
