need an assist here guys.. ac compressor fully functional in the morning. first start of the day. clutch will not engage after the car has been sitting outside in the sun. somehow I am losing the ground to the compressor clutch relay. my book says to test the relay by applying power and ground to one side and the other should have continuity. the top right terminal of the relay harness has battery power so to simulate the continuity as if the relay is working properly, I apply 12v to the bottom right terminal and the clutch engages and ac blows cold. this morning when the ac was working fine I shot for ground at the bottom left terminal and there was ground. does anyone know where this ground comes from and why I might be losing it when the vehicle sits in the sun? I drove about an hour away with the ac working just fine.. when I tried it on the way home.. nothing.

dryer replaced and expansion valve. system vacuumed and serviced.

thanks..

 

The most common reason to not engage when hot is that the clutch gap has grown too wide. Really rule that out by confirming no power to the clutch wire when supposed to be engaged.

The ECU controls the relay. When the A/C button, interior fan switch, evaporator temperature switch, and refrigerant pressure switch are all satisfied, that circuit sends a ground to the condenser fan relay, starting the fan. The fan relay drive is also an input to the ECU. The ECU detects the call for A/C and raises the idle speed slightly then about half a second later grounds the compressor relay coil to start the compressor. If the idle speed is abnormally low and possibly other conditions defined in the ECU software, the ECU does not run the compressor.

So the thing to look for is condenser fan starts and idle speed increases when the A/C button is pressed.

Should also be noted it is not advisable to jump the compressor with the engine running-- if the condenser fan is not on the system will overpressure within seconds and can blow the discharge hose or pop the relief valve.

 

Got it. Thanks for all the useful information. After searching and searching I’m going to try swapping out the climate control first. It already has an issue where all settings for fan work except number 4. After pulling the original out you can see charring on one of the fan switch terminals as well as melted plastic where it mounts to the climate control.

 

problem fixed!!! it was the climate control, the A/C switch to be exact. all of the solder joints were cracked.