Attached are the wiring diagrams for the HVAC. Yes, the PCM turns the clutch on and off, but the relay should have battery voltage on pins 30 (constant bat) and 86 (key on). There are a lot of sensors and switches that can tell it not to turn on the A/C as well. It sounds like the clutch and its power circuits are okay as you did have it working. So, the next step would be to see if the switches and sensors that control the PCM are the issue (likely are).
For testing you will want a test light and a jumper wire or two. First go to the clutch relay and check the socket for battery voltage. Now stick a light jumper into the terminal 86 and put the relay in. Now with the key on touch the jumper to ground, the clutch should engage. If it does, then the issue is on the control side. If it doesn't then check the ground and the wiring to the clutch. As you had it working directly, we'll assume the clutch circuit is good and that it engages with the jumper test. That means you really should have a scan tool with bi-directional control and the ability to read live data from the HVAC and PCM modules. In particular you want to see the two temperature sensors, one behind the grille and the other behind the dash. Say it is 60 degrees outside, but the interior sensor has failed, and it is telling the PCM that it is 40 below inside the car, the heat will work, defrost will work (and it will run the AC on defrost) because it thinks it's very cold. But you won't see any codes without a scan tool. Then there are the low- and high-pressure switches on the system.
The high pressure should be closed if the system is at the proper pressure, it opens if the pressure goes high. A quick test is to simply jump it in the connector. AC now works? Replace the high-pressure switch. The low pressure can be tested the same way.
For any other testing you do need a scan tool. With it you can command the HVAC and see if it's operational or if there is an issue.
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Saturday, May 10th, 2025 AT 2:28 AM
