1977 XJ6C - AC worked perfectly, stopped for fuel, and
restarted car - blows heated air no matter what control
settings, even though compressor is engaged and full charge
refrigerant
Fuses all OK. Hot water valve under bonnet - no vacuum; I applied other
vacuum line, valve closed, so at least not heating the cabin
air (for the moment). Attempted to trace vacuum lines in
dash jungle - no obvious loose or leaking hoses. Flapper
servo has vacuum, but does not respond appropriately to
control settings; it moves Ok with finger pressure.
I conclude either bad temp sensor (Where Is It??), or bad
''Rotary Heat Control Modulator'' - aka temperature knob, or
faulty vacuum distribution due to other cause?
Any thoughts/input gratefully entertained - as well as any
potential source for replacement parts if indicated.
Thanks in advance!
________

 

Are the flaps cycled to heat position, ie:
center facia outlet is now closed
recirculation flaps (at bottom of blower motor housings) now closed, so fresh air flaps are open?

At first blush, what you are describing is what happens when the climate control amplifier fails. The system can cycle to full heat mode and stay there, regardless of selected settings.

The amplifier cotrols servo movement, and two of the functions of the servo is to control vacuum supply to the center facia vent and the heater water valve. The fact that you have no vacuum to close the water valve is a clue that the system has incorrectly cycled, as is the current position of the center facia vent. Recirc flap vacuum supply is controlled through a separate vacuum solenoid, but it also gets signal from the amplifier.

Series II amplifiers are different that Series III, it may be a bit more difficult (and costly) to come up with one. Check out the flap positions as described above and report back if you want more help. Don't draw any inference from the compressor clutch operation just yet.

 

Excellent JTO! The flaps, etc are just as you describe - I'll pursue it as time allows, hopefully this week, and report back.
Thank you!!
________

 

How does one test the AC amplifier, and where is it hidden.....?
________

 

Behind LH console side panel, behind the blower motor relay. There is/ was a factory tester to plug in series to test the system, alternatively you can pull out a wiring diagram and start testing continuity. If memory serves, there is a possibility of the amplifier cycling when one of the inputs goes open circuit, so the best assurance in your case would be to rule everything else out first. The guess based on past experience and probability is that the amplifeir is intermittantly failing. Sometimes they go cold to hot, sometimes the opposite. On occasion you can interrupt the ground (disconnect / reconnect the inline fuse) and the amplifier will cycle back to where you are asking it to be. You can also try cranking on the small potentiometer adjustment screw on the side of the amplifier, and see if it is responsive to the change.

 

-once again you amaze with your expertise.
Fiddling with the potentiometer and removing/reinstalling the fuse does make the system cycle, but only temporarily - it misbehaves again after 2 0r 3 cycles.
Do you have a source for the AC amplifier? It looks like a daunting task to remove the old unit - a spaghetti bowl of wires and vacuum lines crammed into a tight space!
I did find a nice schematic for the HVAC system here: http://tinyurl.com/kod8xz
Again, many thanks for your expertise and willingness to help.
Very Respectfully,
Markus
________

 

Hi Markus,

Thanks for the kind words, and I'm glad to hear you're on the right track. Some squirrel on here earlier this week was trying to make a case that I didn't know what I was talking about after I mis-identified his Mark III system as a Mark IV.

To wit: the link you pasted explains in the description that the diagrams are for '78 and later cars. I'm sure Mr. Squirrel will correct me, but that would be a Mark II system, and yours would be a Mark I. Your car is a Series II Xj6, and uses a different amplifier than Series III..so the diagrams will be similar but not identical.

As for supplying replacement parts, I'll look into the specifics tomorrow and send you a private message.

 

Greetings Markus,

The earlier amplifer is superceded by the Series III XJ6 version, C45402. I have a good used one in stock for $150.00 The two new alternatives to Jaguar ($500. plus) are both aftermarket, the original configuration unit is $325.00 and a smaller, cylindrical style unit is $295. Send me a private message if I can be of further assistance.

 

Greetings JTO! I have found your thread and read it all and I wonder if my 1997 XJ6 has common Climate Control components to these described? My XJ6 has stopped allowing heat into the system, but I tested the Heater Control Valve and it snaps open when 12vdc is applied. The voltage on the connector coming from the Climate Control has a fairly steady 6.15 vdc no matter what temperature setting I enter on the digital control. Any ideas?

 

A 97 XJ has completely different climate control equipment to the XJ Series 1, 2 and 3 1968-1986. The 97 is supposed to be more reliable, is it not Nippon Denso ? I think the old stuff was Clayton Dewandre.

 

reeder, you're heater coolant pump quit.

 

JTO, thanks for the reply. I do not yet know here to find the heater pump. Can you give some description where it is located? I also wonder about the voltage on the connector going to the heater control valve. It does not change from a near-steady 6.15 vdc despite the tempaerature setting in the vehicle. Is there a pwm signal on top of that I cannot see without a scope. or is it as simple as 12vdc pulsed on or off?
Cheers
Russ Reeder

 

Does anyone have a circuit diagram for the "amplifier" which controls the heating /cooling in the XJ6 or know where I can find a circuit diagram. I have tried 2 supposedly working module and both blow hot air most of the time. One gives a/c occasionally. I would like to build a modern equivalent of this controller so that I can have a reliable climate control system. If I can build one then I may consider producing this as a replacement module.

 

Hi, did you ever get a circuit diagram for the ac amplifier c45402? cheers