Testing AC compressor

Basically, the compressor has to be run in a fully charged system to evaluate it's performance. A vibrating needle on the high side gauge would mean that a reed valve is defective.

 

Could you explain how you test an a/c compressor that is installed? I have had two used compressors put in to replace one damaged in a minor accident. I still don't have A/C. The dealer said a valve was probably clogged and took apart the dash to get to it, but that didn't solve the problem. They initially said the compressor was OK, that it looked like it was operating, then changed their minds. One crazy thing is that it sometimes blows cold when I drive up a long, steep hill at the beginning of a trip. I am wondering if something is up with the electronic controls. Thanks.

 

The compressor in the Prius is a scroll unit, and does not have reed valves. You can check the electrical windings with a meg-ohmeter. The scroll itself is pretty dependable. If it has a problem, it is usually very obvious....noise, vibration, etc.

 

If you have / can get a mini-VCI you can do some testing on the compressor while hooked up. The techstream software will let you read the rpms on the compressor to verify that its spinning. You can also manually set various rpms to make sure its responding independent of the climate control system. More simply you can also listen up near the front of the engine when the AC is turned on and hear the whine of the compressor spinning up.

If its connected but the system is not charged there is a procedure in the service manual on TIS for overriding the pressure sensor. I did this a while back to verify that my compressor was still ok after the system had been left uncharged for a long time due to a hole in the condenser. You just don't want to do this for any significant length of time as the compressor will not be lubricated when its not charged.

Without being connected I think you are out of luck. There is a section of the inverter that drives the ac motor in the compressor, and an electrical module, I think they call it the AC amplifier?, that controls it. This module can sometimes fail too, making it seem like the compressor has failed when it hasn't. The Mini-VCI should find this too, or it probably wouldn't be able to talk to the AC ECU correctly. As I recall there is a troubleshooting flow chart in the TIS manual for all this, but it does assume you have techstream (mini-VCI).