Hello guys;

A/C is not blowing cold. Refrigerant is at full pressure, but compressor does not come on. I've got a good tech for problems that are beyond me, and he spent 90 minutes (at no charge, a good guy) looking the system over, reading climate control codes, etc.

He isolated the problem...when he grounds a certain pin to the brown relay in the brake booster compartment, the compressor kicks on and the air blows cold. When he disconnects that ground, the compressor shuts off and will not come back on.

He says that this ground pin of the relay is connected to the ECM, so something there or between the ECM and the relay is not letting a signal through.

I took the car home, and will start to take a look later tonight. Any ideas on an approach? The electrical world is somewhat new to me.

Any thoughts appreciated, especially helpful ones!

.

 

I think it is much less likely to be the ECM or the wiring, and much more likely to be a sensor connectoed to the ECM (directly or indirectly). The primary suspect would be the refrigerant 4-way pressure switch, connected to the ACCM and then to the ECM via an internal communications network. The sensor is located in the aluminum pipe right near the bottom of the fans.

You should try to ground the blue/black wire on the pressure switch and see if that also causes the compressor to come on. If it does, you have a defective pressure switch (assuming you have a proper refrigerant charge, neither too low or too high).

 

Absolutely agree.
That relay is the compressor clutch control. If you jump it and get cold air it is the pressure switch. On later models it is a thermistor but if yours is the snap action type giving it a tap with the handle of a hammer. If the A/C comes on it is definitely the switch.
You can read the aircon codes if you hold down the AUTO and RECIRCULATE buttons at same time and turn on ignition, then push the auto button again and the fault codes will cycle on the display. If you have a "0" code that means no codes.
You will probably have a code 23. See this
https://www.jaguarforums.com/forum/x...de-23-a-74774/

 

Two Steves,

Thanks very much for the tips. I've looked at the schematics, and I see the indication of the blue / black wire you're talking about. I'll take a look at the pressure switch tonight and try your test.

Question from a non-electrical wizard: when you say "try to ground the blue-black wire on the pressure switch," do you mean;

1. connect that wire (or pin) to ground while it's still in the connector, or
2. remove the blue-black wire from the connector and attach it to ground.

I imagine that # 1 is correct, but please confirm.

Also, I've gone through the 1997 documents in JTIS several times, and while I can find several references to the pressure switch, I can't find any procedures on how to replace it. Hmmm.

 

Going by the description in JTIS, it should work if you unplug the connector on the pressure switch and just connect the blue/black terminal to ground with a jumper wire.

If it does turn out to be the pressure switch, it is really not a DIY job, since the refrigerant needs to be evacuated before removing the pressure switch, and then recharged again afterwards.

 

Steve,
Are you sure about that - I believe there's a Schrader valve actuated by removing the switch.
If not there will be a warning notice beside the switch.

 

Really?...I was not aware of that.

 

I'll be VERY careful if i decide to mess with the pressure switch...should probably assume there's not a shrader valve unless it's confirmed somehow. My car is 16 years old this month...any warning label might be gone.

 

The JTIS says remove it, no mention of empty + refill.
Also (and I can't find it) someone on this forum swapped out the 4 way switch cold - just got a quick hiss as the valve closed.
I'd think it would be safe to unscrew the valve wearing a glove and see what happens.
The blowout pressure from the refrigerant is not going to shoot it out like a bullet.
At 10 Bar you'd get 8 kG on a 10 mm dia screw.
ps re your car - I came off the production line in Coventry May 1944.

 

..and a pair of goggles

 

Absolutely. Wearing specs makes one forget such things.

 

European Steve,

Would you mind telling me where you found a procedure in JTIS for removing the pressure switch...I have found several references to the switch but no instructions on replacing it.

 

This is from the 2004 XKR JTIS 82.10.32
Pressure Cutoff Switch
Raise and support the vehicle.
Disconnect the pressure cutoff switch electrical connector.
Remove the pressure cutoff switch.
Remove and discard the pressure cutoff switch O-ring seal.
Install a new pressure cutoff switch O-ring seal.
Lubricate the new O-ring seal with A/C refrigerant oil.
Install the pressure cutoff switch.
Tighten to 8 Nm.
Connect the pressure cutoff switch electrical connector.
Carry out the A/C system flourescent dye leak detection procedure.

BTW - Jaguar spell check obviously lacking. Presumably a flour-escent check involves looking for white powder around the plumbing!!

 

This was the thread that I recall mentioning a schrader valve, it was in the X300 section, but the XK may use the same idea.

https://www.jaguarforums.com/forum/x...failure-56392/

 

Bloody Hell Norri - do you have total recall?
Note to self - never play cards with this guy..........

 

I wish, sometimes I don't know what I did ten minutes ago.

 

Two Steves,

As you suspected, jumping the blue-black pin on the pressure switch harness to ground DOES appear to turn on the compressor.

Indicated code at the a/c panel is 23. So it would appear the pressure switch is indeed bad.

Strange though, even when the pin is jumped to ground and the compressor is on, it doesn't blow cold enough. The tech yesterday said the system was at good pressure. I wonder if having the pressure switch disconnected impedes refrigerant moving through the system somehow.

 

Yes, you got that right. It also controls the fan operation on the other contacts.

 

Well, darn.

A new pressure switch did not solve the problem. I had my tech do it, with me standing at his side, because I wasn't sure if the pressure switch had a schrader valve. It does.

When the car was started up and the a/c turned on with the new pressure switch in place, the compressor did not kick on and the air did not get cold.

I may have misinterpreted things when I ran the grounding test at home the other night - connecting the blue/black pin on the switch harness to ground. When I made that connection, the RPMs of the engine changed, and when I disconnected the ground, the RPMs went back to where they had been. I interpreted this change in RPM as a load on the engine, and interpreted that as a compressor being turned on. Evidently not the case.

(As you may have guessed, I know next to nothing about climate control systems)

The tech says that the ground signal may also tell the ECM to adjust RPM in "anticipation" of the compressor load, a load which in my case may have never come.

So I'm back at square one, minus $ 105 for the switch and labor. The tech is asking that I leave the car with him for a day or two while he further isolates the problem and works up a fix.

 

That's annoying and sorry if we pointed you in the wrong direction but it's hard to see what else it can be.
I don't believe a blown compressor fuse or a defective compressor relay would throw a code 23.
Certainly the other known problem of a bypass door sticking wouldn't.
Any ideas Steve?