9100 a/c issues with the APADS

When the a/c is on and blowing cold the engine fan won't cycle when stopped or at low speed. The APADS detects a fault and shuts the compressor off. If the fan override is on all the time everything works as normal. All the pressure switches and the APADS moduale have been replaced with APADS type. I was told that the problem is with the programing of the ECM. International and Cummins cannot find anything in the ECM. The blink code is 3 red

 

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.

 

Tried that, all the wires check out, the clutch and compressor have been replaced. Everything works until you slow down or stop, the engine fan wont cycle and the head pressure gets to high and throws the fault and shuts the system down. when the engine heats up the fan cycles normally.

 

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

 

It's 3 red blinks. But as stated before, if you leave the fan over ride on there are no faults and the A/C works fine. Leave it off and when you stop the pressure builds and fan won't cycle

 

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.

 

That makes more sense than everything else I've tried, I'll let you know how that works out.

 

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

 

That was one of the first things I did, thanks for the response.

 

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?