My A/C and heat used to work really well. The heat would always work and the A/C would work unless it was really hot out. It would come on for a while then kick off intermittently. Now the problem is that the control unit will not power on at all. I turn the fan switch from off the low and nothing happens. None of the lights come on and the fans will not start. I've tried tearing the whole dash apart trying the chase down the wiring to see where the power comes from for the A/C controls and also the A/C ECU. I was not able to find a fault. I tested the micro switch located on the fan control and it tested good. Does anyone have a wiring diagram for the A/C controls and the A/C ECU and how they work together? All the fuses in the fuse boxes are good and I charged the refrigerant not that long ago. Any help would be appreciated. Thank you.

 

UPDATE I found that I'm not getting battery voltage to the microswitch. I'm reading only .6V across the micro switch. Does anyone know if there is a wiring diagram showing where the micro switch gets power from?

 

Replace the microswitch. Climate control microswitch failure is a common XJ40 problem.
It's happened to me and just about every XJ40 owners I know.
Jaguar offers a kit for about $20 U.S. You can seek out your own microswitch for a few dollars. Search the forum, there's plenty of tech help available about this.

 

Hi nathansallade,

First of all, I'm assuming we're talking about a 1988 XJ40 as in your signature line and not a 1987 as in the title of your thread - let me know if I need to move your thread to the Series III forum.

If your car is an '88, the Electrical Guide does not give any detail on how the power arrives at the microswitch. All the wires to the HVAC Control Panel connect directly to the Climate Control Microprocessor (CCM). I'm not sure if the '88 system is similar to the one in our '93, but the photos at the links below show where the CCM is located on the right side of the Climate Control Unit (CCU):

Welcome to Jag-lovers - Members Photo Viewing Page


The CCM receives battery voltage via the A/C and Radio Relay, which is located on the component panel below the glovebox (behind the passenger-side knee bolster). The A/C and Radio Relay passes along battery voltage from Fuse 10 in the Right Fuse Panel at the bottom of the right A-pillar.

Unfortunately the schematic shows no internal details for the HVAC Control Panel, but its battery power (or possibly lower voltage) must come from the CCM. You could test the pins of the connector to the HVAC Control Panel for an incoming 12V or 5V.

Cheers,

Don

 

The car was made in March of 1987 and imported to Canada. The USA did not get them until 1988. That's I say it's an '88. I just forgot that when I made the title. I got a MK 3 schematic from this site and went through the testing. It seems the micro switch is supposed to connect pin 12 to pin 44. I get the .6V from pin 12. I am assuming that I have a bad ccm. I might just try to take it apart see if i can fix it internally since they are around $100.00 used on ebay. I'm fairly certain there is no documentation on the inter workings of the ccm, so I will just chase the line from pin 12 all the way through the box. Thanks for the help.