XJ6 S3 heater fans/blowers test

Hello, Neither heater fans working. Fuse OK. Power to the brown white tracer wire on relay. ignition on or off. Fans will work if Ii disconnect battery and run a feed to either the red, green grey tracer or blue wires.
a) How do I test the relay? I have a vague memory I repaced this years ago.
b) What controls the relay?
c) Where are these resistors that control the fan speed?
BTW, UK spex car.

I’m away from my resources at the moment but, firstly, do you know that there are four fuses to check? I wouldn’t spend too much time digging until all four have been checked.

Two are in the RH fuse box. One on the amplifier wiring. One clipped to the RH side of the heater case, visible if you remove the ‘cheek panel’.


Hello Doug I did not know four fuses were involved.
Apart from the 50amp, 3rd fuse from the left whicjh is the second one?
I am not sure what amplifier wiring is -is it an AC thing?
Cheek panels- do you mean the ones at knee height either side? I have the left one offto check the relay.

The 50A fuse (#3) runs the fans, Punkydog - a 15A fuse (#6) operates the relays, AC amp andan inline servo. Both must work to run the fans - check

In addition there is an inline 1A fuse to protect the AC amp itself, as Doug describes, and sometimes an inline fuse protecting the compressor clutch . Neither is involved in running the fans.

Red, green, blue at the relay is connected via a resistor unit to give varied fan speeds - they will run the fans when ‘jump’ wire is used. The various relays are operated by microswitches; two at the function control ‘Hi’ and ‘Lo’ and two at the servo in ‘Auto’…

‘Peculiarities’; the fans will not run if the system is in ‘heating’ mode and engine temp is below 40C (104F). Either set the temp control to ‘65’ (cooling mode) or run the engine up to high temp. The retest…

Voltage checks are unreliable; check brown/white at the relay with a test lamp. Due to the high current load; the connection at the 50A fuse may overheat and loosen the wire and/or distort the fuse holder. This may still give 12V

  • but not enough amperes to run the motors…

Beyond that; testing gets more involved…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

Thanks, I am not going to be able to try anything for a few days.
No, A/C I removed it all, spent too much time and money on it.
The ski slope and radio panel has been out so I need to check that the connections on the rotary heater switch.are still OK.
I noticed that when I tested the fans they only appared to run at one speed.

With AC items, amp and servo disabled, Punkydog - you should have 2 speeds. Either ‘Hi’ and ‘Lo’, activated by the function switch. In ‘Auto’ there may be no fan action - it depends on the extent of your AC removals and eventual other back-ups…

The heat related fan functions and fan speed resistors are still active - but the 15A AC fuse is basically redundant, unless used for ‘other’ purposes…

Basically the ‘Hi’ and ‘Lo’ switch functions are best tested at the relay bank…

xj6 85 Sov Europe (UK/NZ)

Update -Warmed up the car -still no fans.

I removed the radio panel, hoping to get access to the two controls, you cannot.

Spent ages shoving the rats nest of audio wiring back plus the fiddly and useless optic light cables.

I thought I had better test the head unit, ignition on, I heard some whirring and movement, fans stated working control was set to demist BTW. Other options appear to work

A bit asthmatic, but I cannot recall them being that powerful anyway. Just got used to modern car fans I suppose.

Noticed recently replaced right hand tank fuel sender playing up.

Thanks to those that offered valuable advice.

I removed and replaced a failed microswitch in the Climate Control Panel Micro Switch and Cams Assembly (AEU2743) in my former 1984 XJ6 Vanden Plas when it failed. It was a real PITA to access, and much worse to remove and replace it with a good microswitch from one of my parts cars, but it can be done and it was the only way I could return the climate control system to full A/C and heater functionality. I also removed and replaced some of the broken fiber optic cables inside the console that were probably broken by whoever installed the aftermarket stereo years ago. That was another real PITA job, but I did it at the same time because I had intact fiber optic strands from another of my Series III XJ6 parts cars because it had the original stereo and apparently no one had torn the center console apart before. This was a memorable project tearing the dash apart to fix the climate control system because it was so difficult to access and remove and replace the failed component.


The whirring sound is the servo re-setting, Punkydog, indicating that the AC amp (head unit?) and servo is working.

In ‘Def’ the defrost vents open, in other positions the vents are closed. The fans run at high speed, same as in ‘Hi’ - ‘Lo’ will give much lower speed. In ‘Auto’ the fans’ speed is controlled by two microswitches at the servo giving medium high and medium low speeds.

(Testing is a bit iffy; if the cabin temps is outside the range, ‘65’/‘85’, fans will run at medium high in all settings. Also, in some versions the medium high is configured to run at ‘Hi’ speed - and turning the temp control also activates the servo
Just for your eventual further testing…:slight_smile: )

Your manipulations may have induced the ‘fiddle factor’ - proper function may not last…?

As an aside, everything working as it should; the air flow is better than on some modern cars I have driven…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

Hello Frank
Head unit: In-dash car stereo control unit.
I am quite sure that it will not last probably dodgy electrical contacts/connections but at present working enough.

These cars appear to be built around the A/C and heater -they must have thought it would never go wrong.