9100 a/c issues with the APADS

Three red is open or shorted compressor clutch circuit. It is also logged from fluctuating voltages, but you would see other problems, mostly headlights flickering or things like that too. I think the fan operation is just keeping it cool enough to not trigger a fault. Make sure the wiring isn't rubbed through anywhere and connections are good between the apads and compressor. You would need to put a multimeter inline between the clutch and compressor and have it on amps and measure what the current going through it is. Most compressors are well under 5 amps, normally about 2-3.5 amps. Let it run until it faults while watching the current flow. It could be going open too and drawing zero amps to trigger the fault as well. Compressor clutch coils will change in resistance when hot to cause problems.

 

Three red blinks is compressor clutch circuit open or shorted.
Two red blinks is high pressure detected.
Which are you getting?

 

Ok, I think the way it specifically works is, the apads tells the engine when to turn on the fan. The apads opens the fan circuit to signal the ecm to turn the fan on. The ecm is watching that input from the apads and when the wire is connected to ground it is signalling the fan to stay OFF. When the wire is open the ecm will turn the fan ON. I have seen this before where the wiring is actually rubbed through somewhere and therefore constantly shorted to ground and so the ecm never sees the open circuit to turn the fan on. So you need to check the fan signal wire between the apads and ecm for being rubbed through and shorted somewhere. The fan signal wire at the apads is Orange. By my diagram it turns to green 23AC, then the next connector turns to a yellow wire with no id which is usually running alone the intake manifold and around the front of the engine and back again, then another connector it becomes 23C tan wire to the 21-way round engine interface connector cavity T.

 

Also check the AC high pressure switch . It could also create the same type of problems as well.

 

Sorry about asking 3 years later… but did you ever solve the problem? My truck does the exact same thing. Was it rubbed out wiring or something else?