Hello everyone,

I have a little problem with my AC system, more precisely; I have never seen it running and want to fix it.
The previous owner modified the AC with a switch to completely turn in on/off, at least he told me this story.
I want to start with this modification, followed the wiring and the switch is directly connected to the compressor.
Here a little illustration (89 XJ 4.0):


I'm not a professional in car electronics, so please excuse the stupid question: Should this work?
I expected a 12V supply to power an electromagnet or whatever mechanic is hidden inside the clutch.

Second question: What are those compressor wires originally connected to?

 

That looks normal. There is wiring you can and cannot see. Follow the wire on the left and it should go to an accumulator (canister) on the frame that has a switch on it.

 

Well, that's the weird thing, I only have those 2 black wires running trough the engine bay and a manually activated switch inside the car.
Followed the wire on the left and it goes directly into the drivers cabin to the retrofitted switch.
Stays in the conduit, no splices or anything on the way. No connection to the fuse box inside the car.
Same thing for the wire on the right, directly connected to the retrofitted switch.
Basically the switch connects the both wires coming from the compressor.

 

It should be wired like I told you. Sounds to me like he wanted to bypass the low pressure safety switch I told you about. Your engine bay looks really clean. You might have a leak down issue due to a compressor seal or bad O rings at the fittings, but looking for the telltale oil spot in a cleaned up engine bay won't do it for you. Does the compressor come on with the switch?

 

The wire from the AC Mode switch should go to the low pressure switch, then to the AC relay. One leg splits off and goes to the ECU. The relay then powers the the clutch and the elec fan.

So when you turn on the AC, assuming there is enough refrigerant charge, power from the blower fuse goes through the mode switch to the low pressure sw, the ac thermostat, to the ECU, and relay. The ECU sees the feed and grounds out the AC relay energizing it. With the relay now energized, it sends power the the AC clutch. It also sends to the fan relay to turn on the electric fan. The ECU should also adjust the IAC to raise the engine rpm.

That ground wire connects to a diode and back to the hot side. It supposed to help the magnetic field collapse when the clutch is de-energized.

Personally, I can't see how that switch can work without any 12v source. Are you sure you didn't miss anything?

I agree with 4.3. It was likely done to bypass an electrical issue.

 

Thanks for the help. Haven't tough about the diode at all, this little guy was also missing.
Removed the conduit today and searched a bit more, found a messy connection with electrical tape in the middle. A diode is also hidden in tape.
One of the black wires is connected to an orange wire. This orange one goes to the relays in the engine bay.

It should send 12V to the clutch, had not enough time to go further. What I expect considering your explanation:


And yes, it's totally possible that there is no refrigerant left. I have never seen the compressor running.
First I want to check the modification and rewire it, make clean connections.
I heard the clutch should have a resistance between 2 and 5 ohms, so I will measure it at this point.
When this is done and OK I will try to bypass the pressure switch for a second. Just to see if the clutch reacts.

If the system is OK; No one refills r12 and I would have to find someone who has compatible stuff, or to change oil and use r134a.
If the system has a leak or the clutch is dead; It's makes more sense to replace the entire 30yo system; compressor, sensor and tubes.
Refrigerant, Seal test, Vacuum etc.are things I can't do by myself, don't have the tools or knowledge.

I take a closer look this weekend. Cleaning those Relay-sockets and wires isn't wrong anyway, everything is black and oily.

 

This is from the '88 diagram if it helps.

 

Bypassed the pressure switch (2 green wires) and tested it. Compressor runs, switch engages/disengages the clutch.
Sight glass on the canister is clear, no bubbles or anything noticeable. So yes, probably there is no refrigerant at all.

Will visit the garage next spring.

Thanks for the help.

 

Good to hear. Let's hope there's no leaks in the system when you get it checked out.