AC switching and wiring

[jkempf]

Been fighting some AC issues with a 2002 US D2 v8 without rear air.

Anyway, first I discovered a small oring leak at the compressor, fixed that and system ran perfect for say a month. Then it started getting grumpy through the hot part of the summer. It would start sort of randomly and run absolutely perfectly but only after a short drive. Then it quit. Just started doing diag and found the freon is still perfect. I jumpered the compressor and the system was working fine. Found the condenser fan lock rotor and the 40amp fuse blown. So I put in a new fan and verified I can run the fan from the relay socket as well as the compressor. So now what I am seeing is that the system is not turning the compressor or fan on at all.

I am sure it is somewhere in the control circuit as the big voltage all traces and operates properly and the system is putting out cold air when jumpered. I cannot get the system to run with any combination of jumpers on the coil side of the two relay sockets and both relays bench test fine.

Is this some sort of ground switched Body Control Unit thing like the alarm problem I fought with? I would think key on and AC switched on and both sides set to low I should get 12V at both relays.

Confused as to the logic of switching the compressor and condenser fan on.

 

[discostew]

Take the underhood fuse box up off its mount and look at some of the connectors under it for burnt terminals and loose contact.

 

[jkempf]

Will do,

Meantime did some quality time with the wiring diagrams. I just checked continuity and voltage of the circuits that go from the main relay to the fan and compressor relays on the coil side of the equation and it all checked out.

The main relay has to be good or the truck wouldn't start is my understanding. The circuits that go out to the FI computer I am wondering about now... Looks like a ground path for the system to prove some sort of engine running condition?

Confused.


2002 US D2 V8

 

[jkempf]

Pulled the fuse and relay panel up and checked all wires for any signs of heat or corrosion. All completely clean and in beautiful shape (which was a shock for the mileage and location in central Vermont).

So down to something dumb that I can't figure out.

Logic would dictate that blowing a 40amp fuse with a fan that was locked and couldn't rotate would say that something somewhere else blew at the same time or overheated.

Anyone know how to test grounded circuits through the Engine management computer for the AC gear? Anyone know if I can bypass or put on redundant grounds and still have proper function?