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There are a couple of other items that will cause intermittent A/C Clutch operation before the switch. First the clutch is operated by a relay. They can get warm and loose connection. The other possibility is a faulty low pressure switch. I have attached a layout for the relay, you can swap it with any known good relay with the same markings on the side. The low pressure switch is located behind the left front wheel arch liner. You can remove the plug and jumper it for testing.
avern1,
My 4-way pressure switch is in a tube that runs along the bottom of the base of the radiator? I need to know how to bypass it to prove it's at fault before I shell out $130 for a part I may not need.
also, there are no relays under the panel LH side (Looking FWD), just brake booster and reservoir. HELP?????
Any further info greatly appreciated. it's 100 degrees in Keller, Texas and I'm glad I another car to drive but I can not stand it when things are down so I'll make the time.....
Sorry buddy wasn't ignoring you. Just got caught in the Honey do trap. LOL.. I have attached the wiring schematics for the AC system. I guess the first challenge is finding the AC relay. Since your AC works intermittently I am hesitant to condemn the pressure valve. I am still leaning towards a faulty relay. Take a look at the diagrams and see if they help.
This seems like I could remove the connector and ground UB (Blue with white tracer) wire and it should bypass the pressure switch.....and if the pressure switch is bad the compressor clutch should engage.
I'm concerned about the note underneath that says " NOTE circuit revised VIN number" but I can't read it the vin number.
Let me know what you think, and that goes for all you tech minded souls with a honey do list!!!!!
Michaelh,
Thanks for the info...you are correct also..... my notes say UB is Blue/Black.....but typed Blue white??????
My question is still the same ....
1. When the a/c fails to cool....(remember it's intermittent)...and clutch fails to drive the compressor....I want to bypass the 4-way pressure switch to PROVE that the switch is the problem.
BUT, I just read in the Jag service training manual that, "During normal ambient temp conditions the switch contacts should be closed." If that is the case, does one of these contacts OPEN if pressure get's too high? If not....is there another high-pressure switch?
I have a new switch on order.......but don't want to vacuum and reservice the system unless I prove the switch to be faulty!!!!!!!
If you look at the 4-way switch in Vern's diagram, you can see that the top item is '2-30 bar'. This sets the lower & upper limits for the compressor's operation.
I found an article (it's for the 2001 XJ, but relevant) which explains the switch operation more fully:
" Pressure (Bitron) switch:
• Located in the discharge pipe.
• Provides a signal, via the A/CCM, to the ECM, to disengage the compressor clutch should the refrigerant
pressure be < 2 bar or > 30 bar.
• Provides a hard-wired signal to the ECM, to switch the cooling fans to HIGH speed at 22 bar rising pressure
and to LOW speed at 17,5 bar falling pressure.
• Provides a hard-wired signal to the ECM, to switch the radiator cooling fans to LOW speed at 12 bar rising
pressure and to switch the fans OFF at 8 bar falling pressure.
"
Michaelh,
EXACTLY what I was looking for! Thank you so much. It looks like WU and YW just control the fan operation and are both normally closed in normal operation. Looks like UB will normally be closed in normal operation if pressure is between 2 and 30 BAR.
Soooooo.. If I drive it until the compressor quits....and the pressures are still good....my assumption is If I put a ground to UB and the compressor runs....I have a bad switch and it's worth buying a new one, evacuating the system and installing new switch.
Yell out if anyone sees I'm missing something here.........I HAVE been wrong before.
My compressor used to quit after driving for awhile. It ended up being a worn AC clutch. The magnetic clutch couldn't overcome the clutch air gap when everything heated up.
Understood, and that is still a possibility, thank you. That's exactly why I want to prove the switch is bad before I replace it. Last week after the clutch failed to engage I bypassed the control circuit by running 12v straight to the clutch and it engaged normally.
OK....most people don't want to admit when they do something stupid....me either. But, I hope this helps someone down the road. Bypass of switch showed switch was good....still no power to the compressor. But I still could not find the relay for the clutch...and I swear it was NOT in the LH forward bulkhead area with the brake booster as I looked there TWICE! Turns out at 61 years old I'm going blind....................... because right there in front of my damn face IS the small relay box slightly tucked under the hood seal on the outside wall of the "forward bulkhead area"! AND....the relay was just resting in the slots and not pushed in causing the compressor to be intermittent. Now, all is good for days. some days you just have to step back, grab a beer, and say.....what am I overlooking!
Anyone want to buy a used 4 way pressure switch?????
Good to hear that you got it resolved. I always when dealing with my Jag electrical problems start at the fuse, then go to the relay, then the switch and last to the device.
06-28-2018, 01:23 PM
