Hello everyone,

The long path to getting my 1986 SJ6 up and running has been bearing fruits - the car runs and drives quite well now and I have slowly been restoring bits and pieces. I’m currently on the aircon system (I’m in Arizona so it’s a necessity).

Right now the system runs sporadically and the fans occasionally come and but not for long. I started with the vacuum system but that appears to be working well. So on to electrical. I’ve been using the excellent Jagtech wiring diagrams and the service manual. I notice when I probe power at the main set of relays I get a solid 12v, but the brown wire going to the amplified is less than 2v. Is this normal? I can’t see a reason for it in the wiring diagrams - seems like it should be a full 12v. If it’s not getting the full voltage does that mean a poor connection coming from the mode control switch?

i also note that the coolant temp sensor on the line above on the left side is disconnected. I have shorted the brown and brown/yellow wires resting there to bypass this.

There are a couple of other loose disconnected wires there as well, one pink and the other black. Per the wiring diagram these are supposed to be connected to a vacuum vale, I think? I can’t see one near there though. Anyone know where these go? Pic is below showing the loose wires.

 

Yes, you should be getting 12v on the brown wire. Could be a dirty switch, or bad connector at the switch.

The drawing below from the Delanair II manual shows the solenoid above the cheek cowl outlet in your photo.



Jon

 

Thanks!

I notice if I disconnect the round connector on the right side to the servo the voltage is normal, or close to it, on the brown wire circuit (10.5-11.5v, depending which position the mode switch is in). My battery is a little low too since I’ve been messing with this for the last couple of days.

I’m assuming the servo is bad. Has anyone had success taking these out and cleaning or revitalizing them or is a replacement in my future?

 

It may be that the switch or relay contacts cannot support a load required to power the amp and servo. With the servo and amp disconnected, you see full voltage. You need to rule that out first. A 12v light bulb that draws a couple of amps should verify the circuit.
Here's a video that shows how to test the servo by itself. If it operates during those tests, look elsewhere.
Jon

 

The symptoms sound like you possibly have a bad microswitch on the mode control. It has 4 microswitches, one of which is the main on/off switch. This connects incoming power on the green wire (from fuse #6) to the brown wire which feeds the amp and servo etc. If the internal contacts of the switch have become dirty, that could explain the voltage drop.

On my car I was finding that the system would not turn on, or sometimes it did but only for a few seconds. Changing this microswitch solved the problem.

It is quite tricky to get the mode control switch out and if you do, take a photo or two first to help remember which wire goes where in its terminals.

Suitable replacement microswitches are available from electronic component retailers for very little cost.

 

This indeed sounds very similar to my issue. In my case the system does usually blow for a few seconds, especially in the "low" position, but if I turn it to auto or high it shuts off completely. If it's one of the microswitches at the mode control knob, can I test resistance through the harness to confirm before taking it apart?

 

Resistance won't tell you squat, unless the circuit is under load. That's why you need a test light with reasonably high resistance to load the circuit; if the light glows bright, its good. If dim or it goes out, it's not.
A relay, switch, plug contact, or partially broken wire can test fine with a multimeter, but fail miserably under load. All a multimeter will tell you is if the item failed so completely that it won't carry current under a no load condition.

 

This has me getting ready to delve back into that switch again on mine, only been checking with ohm meter for continuity!!! Never even crossed my mind about draw!!! Will be great if this fixes my issue!! ( same as others, intermittent operation)

 

This is perfect timing, my system has always worked perfectly. Yesterday I took the car out for a drive, the A/C was on and it was cool out so I turn the system off. I decided to add some heat, when I switched the knobs to temp and low nothing. No power to the blower, no sound of the servo motors when I adjust temp!!! I check the line fuse on each side of the transmission both are fine. Anything else I should check before getting into deep investigation??
79 XJ67L

 

If you turn a/c back on by setting it on cold temps, do all three speeds of blowers work? If so, you know issue isn't with your blower or blower relays.
If you turn the fan knob to defrost, does the center vent close, and sir start coming out of the defrost vents? If so, Is that air hot or cold?
The blowers won't come on for heat until the water temp switch for the a/c closes one the water temp warms up. If you short across the connectors on its terminals, blowers should come on when heat is selected. If they do, then that switch is bad.
Here's a description and location of that switch.

 

Post #2 of this link has copies of two Delanair manuals.
https://www.jaguarforums.com/forum/x...manual-256066/
Jon

 

Thanks Ill look this evening, it was just a all of sudden thing, worked then stopped, no power for anything AC, heat, Defrost, which is why I assumed it was a fuse (or at least hoped)

 

Remember…. the system has four fuses. You’ve checked the two in the console so now check the two in the fuse box

Also, before going too far into the weeds, clean/tighten all the connections at the relay pack behind the console cheek panel, left side.

Cheers
DD

 

tried that, all 4 fuses have been replaced, all the wiring and connections look like new, must be the relay pack

 

This is excellent - I did a bit of a search on Youtube but this guy's videos eluded me. They're great!