This is for a 1999 Ford F150 Lightning. The truck has a Whipple 2.3L on it so I am hoping the issue is not in the tune. A lot of work was done to the truck at one time, but it has not worked since the supercharger and some suspension/tub upgrades.

I got the schematic and traced where I had voltage.

Please help if you can!



-12V out of Low Pressure Clutch Cycling Switch [BLK/YEL] only when AC is demanded on.

-0V at BJB to PCM [PNK/YEL] when AC clutch relay #204 is removed. 12V when relay is in place, whether AC is demanded or not. I tested this terminal 2 relay port (with relay removed) wrt ground and got 9.45 kOhms of resistance with vehicle key in run position (AC demand didn't effect). Out of Limit with key off.

-12V at BJB to Engine Controls System (PCM Power Relay) [RED/YEL] whether AC is demanded on or off.

-12V coming from central fuse #5 into BJB AC clutch relay (If I jump this over to the output I can make the clutch engage).

-Switched diodes with other one, and tested with Fluke, seems fine. I tested the resistance across the diode ports (effectively I think this should represent the resistance across the clutch terminals) and got 3.4 Ohms.

-I have swapped out the AC clutch relay (I guess its known as WOT relay on schematic) with other relays and it didn't help.




Based on this it seems to me like the PCM is not grounding out terminal 2 on the AC Clutch Relay #204, but from my understanding it should be.

I do have P0602 code, PCM Malfunction, but with the Whipple tune I just don't know.

 

If I ground the terminal 2 on the relay it does engage the clutch. So the PCM or tune seems to be the issue?

 

Yes. The clutch is software-controlled.

Call whomever did the tune.

 

I called, but was not helpful. They state they would have never messed with AC settings, which ultimately makes since, but does not help me any.

Unfortunately it seems my PCM may be bad? But then I would have to find a way to load the whipple tune.

I could use the low pressure 12v signal and bypass the PCM with another relay to provide ground to the current clutch relay. Unfortunately I don't like loosing the PCM logic. Does anyone know the full PCM logic. Disable under X% throttle and what else? Coolant Temp? Startup time? Min/max Rpm?

 

My problem turned out to be a bad instrument cluster. My pick-up had automatic climate control and apparently a/c circuits are tied in to the instrument cluster. I replaced the instrument cluster and the a/c now has power and is working fine.

 

Since you FAILED to identify what you have, your comments are not useful and simply do not apply to the vehicle under discussion here.

Why did you feel compelled to post the same almost useless information in so many threads?