The heater and air conditioning does not work on our 1978 XJ 4.2 LWB (The air con only works on demister) . Pulled the dash out and there are a lot of possibilities but where do we start. We have Replaced the climate control module but still not getting any air except out of the demister. It's going to be an expensive exercise if we don't know what to tackle first. Can anyone suggest what and how to fix this problem. Many thanks

 

hi,
I am familiar with the 1980-on a/c system, but if the 1978 is somewhat similar, and only the demister Vents are working, this is most likely that the SERVO unit is not rotating, and probably due to a loss of vacuum. {the Servo is like a miniature 'crankshaft' with electric switches which opens and closes the different Vents according to what is selected with the Selector Switch by way of Rods; in the Series 3 the Servo is located on the front passenger side of the center console, to the right of the radio}. Remove the upholstery Vent panel that would normally be near the left knee; Normally the Servo has a black plastic cover on it, at least in the Series 3 it does.

Also in the Series 3, (1980-1992) there is a little plastic black & white Check Valve located hanging next to the battery, connected on both sides by vacuum hoses that go through the firewall/bulkhead into the cabin and connect to the SERVO.

test the Check Valve by removing it (first note which side goes where), and blow through it on both sides; These have a tendency to clog and stop the Servo from acting. If no air comes through either side, put it in a pan with warm water to try and unclog it by letting warm water get in it, and blowing on it every now and then; You should get air coming out through one side but not the other when you blow on it.

If that Check Valve tests good, then the next step is testing the Servo itself.

first test is to make sure the Master Rod is actually connected to the Servo, these come loose at the connecting fitting. The long Vertical Rod is the Master; Pull it up / push it down to make sure it isn't loose at the screw fitting.

this all assumes the system is somewhat similar to the Series 3. Otherwise someone with knowledge of a Series 2 will need to help you.

 

Good advice from Jose.

FTR, the Ser II and Ser III Climate Control are virtually the same. Both Delanair MkII with only minor changes during the later Ser III production.

All automatic function is bypassed with the mode selector set to "Deforst" ( or demist, or whatever it's labled)

Personally I would begin this way:

Set the mode to "Auto" and slowly turn the temp selector control. Do you *hear* the servo respond? You should hear a whir-type sound and maybe hear the linkages and flaps actuating as well.

If you DO hear noise then we know the system is at least trying to follow commands, even if it can't succeed.

If you DON'T hear the whir, check and/or replace all four system fuses and make sure the fuse clips/contacts are corrosion free. Bear in mind that a fuse that isn't burned might not be good. Old fuses will sometimes have the wire broken off under the steel end cap.

On a Ser III the fuses are located as follows
-One in the left side fuse panel
-One in the right side fuse panel
-One on the amplifier ground wire
-One clipped to the right side of the climate control casing

I suspect, but can't confirm, that they're located in the same places on a Ser II

Cheers
DD

 

oh oh, this user is in Australia! it's a RHD car! everything could be on the wrong side!

 

In THIS case I don't think it matters.

However I've often wonderd if the left and right fuse panels and component panels were in the same, or reversed, position--LHD versus RHD?

Cheers
DD

 

when it comes to XJ, I have no clue either. but if my '65 S type serves as an example of LHD vs. RHD, then most everything is reversed sort of in a mirror image, including the gauges, except one thing was left RHD: the Hood Release pull; in my LHD S type, the hood release is on the passenger side, (as in a RHD car), whereas the hood release pull in my '84 LHD XJ-6, is on the driver's side as it should be. The curious thing is that the S type's sheet metal has part of the built-in bracket for a LHD hood release pull on both sides, but Jaguar did not see it neccessary to install it on the left side, probably because the S type was more of an experiment with the E-type's IRS, made for a short 4½ year run in which only around 24k S types were built for the entire world market, and this is happening while they were still building the MK-2 in 240 and 340 badging, and while at the same time they were introducing the 420 in 1966 AND preparing for the debut of the Series 1 XJ in 1968. In other words, they must have had a big mess in their hands to worry about a hood release cable, or it simply flew by them. Since the main fuse box in the S type is in the center, it doesn't apply.

 

Doug, Jose, Anita,

The S2 fuses are under the steering column = main fuse block.

The amp fuse is on the LH side in the earth wire near that round multi-pin plug, sort of tucked in behind teh multi relay pack for the fan speeds.

The other fuse is on the RH side, attached up behind the tin floor vent of the casing, and being RHD, the handbrake stuff is in the way, and it is just plain PITA to get at. I do that one by feel now, coz I have done so many I know exactly where the little bugga is.

The S2 had no fuse box on the LH side as did the S3/XJ-S cars, well all my S2's did not.

That fuse behind the handbrake is the main issue with most I have been involved with, and I always fit a 15amp in there, no exceptions.

As said, vac supply from the engine TO the inside of the car can get hissy, and that "one way valve" STICKS, and reeks havoc as we know.

 

Apologies for my delay in replying - nothing to do with the time distance just me. I find technology very frustrating yet amazing when I get it to work for me. I was overwhelmed to read that Doug and Jose, followed by Grant, took the time to quickly respond to our heating and cooling problem and with such detail and depth of knowledge, also allowing consideration for RHD. Thank you. We will try the suggestions you have provided over this coming week and write back, hopefully, to share our success.

 

Aw, it's nothing, really. We're just in love with the sound of our own voices. Wind us up and we'll go on endlessly :-) :-)


Good luck,
DD

 

who? moi? :-))

 

How true.

The wife has "selective hearing", and I always thought that was a male infliction haha.