I just used my AC for the first time and found out that the system is no functioning properly. Blower motors work fine but only warm air comes out of the vents. I charged the system hoping that would solve the problem but no luck.

It appears that the compressor is not kicking on. I am very very much a rookie when it comes to air conditioning. I don't even know what the compressor clutch is or where it is located to know whether it is operable or not.

If anyone can offer any AC help or pointers, I would really appreciate it. Thanks

 

The compressor clutch is in the center of the pulley on the front of the compressor that rotates via the belt. When it is energized with electricity by the AC switch it locks the shaft in the center to the pulley and that turns the compressor. When not engaged the center part of the clutch/pulley should not be rotating along with the outer part of the pulley and belt.

When you turn on the AC yous should hear a click from the clutch indicated it is engaging the to the pulley. If you don't hear a click it may not be getting power or is not working. When working it should start rotating along with the pulley

Also when the motor is off, see if you can rotate the exposed part of the clutch while the pulley is stationary. If not it isn't working properly.

Hope this helps

Bob McCormack

 

The clutch does not engage. However, it will turn with the engine off. I guess I will need to check for power to the clutch.

AC fuses look good and I cleaned the relay contacts. Where would I start to see if power is being delivered to the clutch?

Or is it better to simply replace the entire clutch/compressor unit?

 

The compressor clutch is controlled by 2 wires in a separate loom...... On my car there is a joiner just before the compressor so you can easily unhook the wires and test for voltage....

If you can find this loom on your car it gives you the chance to do 2 pieces of elimination work.....


1) disconnect the loom and check for voltage across it when you turn the A/C on


2) Rig up a temporary connection straight to a known power source and see if the compressor starts

Did you ever have A/C ? or is this the first time you are trying to get your A/C working since you owned the car ? On my car, when the compressor engages, it's quite noticable, ie the idle drops a little bit and my already bad fuel consumption gets worse, but at least I'm cool :-)

 

I just tried the AC for the first time. The compressor has never kicked on. All of my other issues with the car have been electrical in nature and I've gotten most of those bugs cleared up. I'm hoping that this will work out the same. It's just that AC units scare me because I'm so unfamiliar with them. I don't want to turn what may be a couple hundred dollar issue into a couple thousand dollar issue because of my ignorance.

Thanks for the information

 

The clutch is probably not getting 12 V power from the AC system. Do what Sarc says to test it. If the clutch clicks and turns the compressor it is good. Then you wil know where the problem is. Still may not be an easy fix as these AC systems are computer controlled and quite troublesome.
RagJag

 

As RagJag said, even if you find out you have a power issue going to the compressor and get that fixed, it still won't guarantee you will get cool air...... take it step by step and we'll get you cool again (eventually)

 

I know that you said that you had the system recharged but is it still holding pressure?
There is a pressure switch that stops the compressor operating if the pressure drops too low. I think it is because the gas contains a lubricant that keeps the compressor sweet and if it leaks out then the compressor will run its bearings.
I had this happen on a series 2 XJ12 a long time ago; quite spectacular with long lines of sparks exiting either side of the bonnet at night at 80mph in the fast lane.
Had to pull over and cut the belt off to carry on.
Steve

 

Thanks for all the info.

I didn't have a chance to work on it last night. I will have some time tonight and I will report my findings. My protocol will be this: 1) make sure power is getting to clutch 2) determine if the system is holding a charge and 3) come back here and beg for more help.

Thanks.

 

Ok. I determined that there is no power to the compressor clutch under the normal setup. Further, when I wired power directly to the clutch it did engage. So, now I know that the compressor does work or at least that it will turn on when given power. I also checked the charge and the pressure is holding. I have power to the relay so somewhere between the relay and the compressor I am losing power. Does anyone know how/where the wire travels from the relay to the clutch? Thanks

 

Some more information:

When I test for voltage coming into the AC relay, both incoming lines read 12+ volts. That tells me that the dual pressure cutoff is not the source of my problem because if it were, there wouldn't be power to the relay from that line, correct? In addition, it tells me that my AC or compressor switch is functioning as well for the same reason listed above.

I'm getting all of this by trying to read the circuit diagram. Am I correct or do I need to give up trying to read a circuit diagram?

Thanks

 

I did that. When I powered up the compressor directly, I used the relay input as the power supply. Also, I switched the relay with one I knew was working and still no power to the compressor. Further, the relay I took off of the ac line works in the location from which I took the replacement.

 

When you recharged your AC with refrigerant, you should have noticed the Fan Clutch engaging while doing so. If it didn't engage, you didn't get a complete charge of coolant anyway. Follow Sarc's suggestion and by process of elimination you will determine the problem. Assume it is something simple before looking at the ECM/ECU. More than likely there is a faulty contact (electrical) somewhere or it isn't holding any refrigerant. When you find it, it will likely be something simple more often than not.

 

I felt like I was getting close to the source of the problem but I am getting more confused. I'm going to list what I know is going on and see what you guys think my next step should be.

1) AC button on and in manual control = no compressor spin and no voltage across the loom to the compressor.
2) applying direct power from the power input at the relay connection to the loom at the compressor = spinning clutch/working compressor
3) refrigerant charge shows adequate pressure at the low pressure valve. I am nervous to add more and overcharge the system.
4) relay swapping does nothing to fix situation so not a bad relay.

 

Do you have power from the relay? It sounds to me as if it could be faulty. Try bypassing it with a feed from the relay input supply directly to the compressor clutch and see if it works.
Steve

 

Are you getting power to and from the A/C switch? It might be worth taking out the panel and bypassing the switch to see if that is the problem.
Also, have you checked the fuse for continuity? It may appear to be ok on a visual inspection but still be faulty.

 

That first point is what I have been thinking. Please excuse me if you have already done this, but I am not clear completely about what has been tested and what has not. I suggest therefore, on the basis that applying current directly to the compressor makes it cut in OK:

1. identify the relay that switches on the compressor clutch and make sure the high-current feed side of the relay has power when car is running and the aircon is switched off at the aircon control panel. If it does not have power (ie even if the relay closes it is not receiving any power to switch) that is part of the problem.
2. Then identify the low-current feed side of the relay that should go live when the aircon is called for from the control panel, and see if this goes live when the aircon is switched on. If not, that is part of the problem.
3. Test for continuity between the control panel switch and the relay; test for continuity between the relay and the compressor; test for continuity between the relay low current earth side and earth.

Between them, all these should help to narrow down where the fault is. Post the results and I am sure the guys will sort it.

 

Thanks. Here is what I've found. The high current part of the circuit has power constantly when the car is on. When I press the AC switch in the car, the low current side gets power. However, the power never gets to the compressor. So, I'm thinking that the problem lies in the wiring from the relay to the compressor. But how do I find out where the problem is without rewiring the entire line from the relay to the compressor.

 

Great so far. Next question:

Does the high-current output side of the relay (ie the relay pole that feeds current to the compressor) go live when you press the aircon button? If it does not, the new relay is also at fault.

If it does, you have a break of continuity in the wire from the relay to the compressor. You can verify this by switching everything off, then disconnect this wire from the relay, and applying 12v to it, and see if the other end at the comprssor gets 12v. If you have been putting any screws in anywhere, it is VERY easy to penetrate the loom and inadvertently break a wire.

Running a new wire down the outside of the loom wrapper is the simplest way to fix this, but for the pure at heart (not me!) opening up the loom and finding the wire break and fixing it is the other way.

Greg

 

Thanks. I will try to see if the output goes live with the relay in place this evening.

I am not a purist and assuming the relay is good, running a completely new wire to the compressor from the relay output seems much simpler than trying to find a break in the existing wire.