so my dads 98 xjs a/c is not working. the entire system checks out, the problem is the compressor clutch relay is not getting 12v to pin 86.

the system is charged fully with no leaks. i tested the line going to the ac clutch for power and get nothing. i then jumped a wire from the 12v+ battery terminal to the ac clutch line and the clutch turns on just fine and the system starts blowing cold air. there is a relay in the engine bay for the ac clutch. pin 30 is getting 12v+ with the engine on, pin 87 is going to the ac clutch, pin 85 is making ground just fine but when i voltmeter pin 86(i assume this comes from the ecm) i get fluctuating voltage from .8-3.7......none of which is enough to activate the relay and turn the clutch on.

is this and ecm issue? i have already tried different relays, and i tried swapping the hvac switch panel inside the cab with one from my 01. i also compared the same relay function on my 01 and eveything is the same, but mine gets 12v+ on pin 86 when the ecm wants the ac clutch engaged. my ac system is working fine.

i would try swapping my ecm with his, but my thinking is that wouldnt work because there are too many engine control differences between my 01 and his 98.

so whats my next step? is there any other switch or sensor i should test here? or is my only option to swap in another ecm and see what happens? if i look for an ecm i would find one from a 98, but does it matter if it is auto or manual? his is a 5 speed.

thanks for any help.

 

Check your high and low pressure switches.

 

You should have 12v constant at pin #30 From fuse nine at PDC.
Pin 87 goes to the clutch.
Pin 86 FUSED IGNITION SWITCH OUTPUT (ST-RUN)
Pin 85 is ground from the PCM to activate relay.
Mine is 2000.
http://www.google.com/imgres?imgurl=...QEwAw&dur=2093

 

this is good to know, thank you. i was wondering whether it was the ground or 12v+ that activated the relay, now i know.

now that i think about it more my money is on one of the pressure switches, gonna check those tomorrow. can i change a switch out without discharging the system?

 

Yes,you can.