A/C Compressor Clutch won't engage
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Instructor
Joined: Apr 2012
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From: Arvada Colorado
A/C Compressor Clutch won't engage
Hey guys. Thanks in advance for all your help. I have a '99 manual with just the single controls for HVAC.
I'm having some A/C issues, I can't get my clutch to engage.
I found the schematic that Bill Curlee posted and followed it through and checked that fuse 24 is good. I also jumpered across the relay 34 contact and found that my clutch engaged. At this time I read the pressure on the low side and found it to be low so I added some Freon to get it up to within the green zone on the can (based on the ambient temperature).
This initially lead me to believe the relay was bad so I saw that the horn relay was exactly the same so I tried swapping and found the clutch would still not engage.
Now I'm thinking there is something wrong with the A/C Refrigerant Pressure Sensor. Where can I find this? And how am I checking it? Am I looking for 5V on Pin C if it's working?
Anything else I can look at? There is the A/C Clutch Relay Control in the PCM but I wouldn't really know what to do there.
I'm having some A/C issues, I can't get my clutch to engage.
I found the schematic that Bill Curlee posted and followed it through and checked that fuse 24 is good. I also jumpered across the relay 34 contact and found that my clutch engaged. At this time I read the pressure on the low side and found it to be low so I added some Freon to get it up to within the green zone on the can (based on the ambient temperature).
This initially lead me to believe the relay was bad so I saw that the horn relay was exactly the same so I tried swapping and found the clutch would still not engage.
Now I'm thinking there is something wrong with the A/C Refrigerant Pressure Sensor. Where can I find this? And how am I checking it? Am I looking for 5V on Pin C if it's working?
Anything else I can look at? There is the A/C Clutch Relay Control in the PCM but I wouldn't really know what to do there.
Last edited by tycksena; Jun 8, 2018 at 12:27 PM.
Zen Vet Master Level VII
Joined: Mar 2016
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From: Southlake, TX
The fact that you were low, tells me to check the low side first. The sensors are located on the steel lines of your AC.
If you think you have enough AC, reset your system by disconnecting the battery so as to get a full, fresh reading.
Last edited by billschroeder5842; Jun 8, 2018 at 01:24 PM.
Thread Starter
Instructor
Joined: Apr 2012
Posts: 111
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From: Arvada Colorado
This is the right direction. There is a low pressure sensor and a high pressure sensor.
The fact that you were low, tells me to check the low side first. The sensors are located on the steel lines of your AC.
If you think you have enough AC, reset your system by disconnecting the battery so as to get a full, fresh reading.
The fact that you were low, tells me to check the low side first. The sensors are located on the steel lines of your AC.
If you think you have enough AC, reset your system by disconnecting the battery so as to get a full, fresh reading.
When I checked the low side it was at 32 psi. How would I go about verifying that the pressure switch is working correctly? I'm assuming it's difficult to replace the pressure switches as those lines have pressure on them. Would probably have to remove any Freon from the system.
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Joined: Feb 2018
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Remove the low pressure wire connector at that sensor then jumper across the two wires in the harness plug. If the clutch engages, you either still have low Freon or a faulty pressure switch. Most complete connections from an ECM or PCM are the result of a ground being provided rather than say, 5 volts. When a PCM commands something on, it completes a ground circuit.
Last edited by grantorino; Jun 8, 2018 at 08:29 PM.
