OK, I'm new on here but have searched and can't find an answer for my problem, its a 98 with climate control. Here's my problem; air is not working in auto or manual settings, took to shop and pressure was fine, when you hit the air button on dash it blinks 3 times but clutch doesnt engage, check fuse & relay & both ok, I am not getting any voltage to the high/low pressure sensor and when I jump across it nothing, I can jump across the relay at pins 3 & 5 and the compressor kicks on, have switched relays with same results. I can take and run a jumper from a good ground to the ground side of the relay coil and the compressor kicks on but still nothing at the hi/low pressure sensor. not sure if it is an ambieant sensor or even how to check them. Any help would be appreciated, Thanks

 

The low pressure switch just grounds out the circuit so one side should have ground and the other goes to the PCM.

The high pressure switch connects the A/C REQ output from the HVAC control module to the PCM.

The PCM tells the A/C compressor clutch relay to energize by completing the ground circuit.

Here are a few wiring schematics for you: