Prostar a/c going hot

CK 4 BAD CONN AT comp.

 

The a/c is all computer controlled. Two common problems will shut down the a/c after running for a bit. The temperature thermistors, or circuits will screw up, or the high pressure sensor or circuit will screw up. If the high pressure screws up and the system reads too high or too low a fault will be logged in the body controller. The body controller will not allow the a/c run until the key is cycled. This can be caused from a failing sensor, corrosion in the sensor connector, loose terminals in the sensor connector or broken wires in the harness usually at the sensor because it makes a sharp bend there. The thermistors tell the body controller how cold the evaporator is to prevent freezing. If there is an open circuit due to either a failed sensor or wire the body controller reads zero degrees F. Since the body controller is seeing the evaporator is cold enough it doesn't allow the compressor to turn on. All these problems can take a long time to become active. Typically when the truck is in the shop, the engine is cold and the truck not moving, and so the system works. If the body controllers are not logging any head pressure codes I would replace both thermistors and make sure the body controller software revision is up to date.