88 4cyl 5sp w AC, finally got AC working excellent except relay won't trigger on. What tells the relay (in front near receiver dryer) to go on? I did just read in my searches that said relay may be on left or right, I replaced left yesterday and AC clicked in and worked great, not sure which relay is high fan and which is AC ?
Was wondering if switch panel starts relay, but switch must be good coz fan goes on and idle goes up.
Thanks in advance

compressor relay or front a/c relay?

the 25a heater a/c fuse powers the front a/c power relay & the control head.
The control head turns the relay on, sending power to the blower switch and comperssor relay (by the fuel pump relay in back).

Does the blower motor work? If the blower motor works the a/c power relay is working.

The high speed blower relay wire colors are orange,black,purple and red
The A/C power relay wires are pink, 2 browns and black

That's good info, I found my AC relay was on the far right side, it was supposed to be the other one, and I replaced it and everything works fine now.

OK I spoke too soon, relay in front won't click in. I guess next I'm looking at the switch panel? Not sure where to go from here.
When I can get ac to work its ice cold, now I need to figure out whats up.
On second thought switch panel does turn on the radiator fan and bump up the idle, does same on defrost, max, norm as it should.
I'm studying the diagram posted plus I have FSM to follow, love this work when its successful, dread it when its not.
Could the ECM not be putting out the signal to trip relay? Got new relay at Azone, initially put it in wrong location, next door is fan high speed relay, finally figured that out, high speed fan works great. So now my new relay is not tripping the compressor to engage.
Where do I go next???
Thanks for all your help guys.

Did you test the pressure switch? If you're low on refrigerant, it won't let the compressor clutch kick in.

Mine does not have a pressure switch on the receiver dryer.

4 cylinders have a high and a low pressure cutout switch on the back of the compressor.

The control head has two different power wires coming out for the AC: one for power to the compressor, the other powers
the compressor relay and signals the computer to turn on the fan/raise idle and turn on the compressor relay if the freon pressure is right.

With key on & the control head on AC, check for power with a test light at the BLACK/WHITE compresser relay wire -
you should have power if the control head is working ok.

Next, check for power at the LIGHT BLUE wire on the compressor relay.
You should have power if the freon & pressure switches are ok (sounds like you have power if the fan comes on & idle raises).

If eveything checks good so far start car/AC on & check for power at the GREEN compressor relay wire - if it has power you have a wiring problem
to the compressor or a bad compressor clutch.

If no power at the GREEN wire, ground the DARK BLUE wire - this bypasses computer control & the relay should turn on, you should have
power at the GREEN wire & the compressor should turn on.
If this works the computer is not turning on the compressor relay.

The relay you want is in the back in the engine compartment, next to the fuel pump relay, kind of behind the driver's head. It's the one with the light and dark blue wires.

With the V5 compressor, you need at least 8 psi on the low side for the compressor to kick on. Hook up a gauge set to make sure you still have refrigerant, it may have leaked out. As you mentioned, yours doesn't have the accumulator mounted cycling switch, it's controlled by a valve in the compressor itself.

I was so busy messing w the front AC relay I forgot about the one next to the fuel pump relay. I'll bet that's it .
Those are good tests mentioned above, if the relay isn't it I'll have to go testing.
Thanks