1994 XJS climate control not working properly
 

I have a 1994 XJS convertible that only supplies hot air through the vents. It may be no concern, but I have no vacuum present at the hot water valve supplying the heater core. Any suggestions?

Much thanks for any and all help!

No vacuum at the heater hot water valve is normally open positron all the time heat is selected as long as AC is not selected. Selecting AC supplies vacuum to the valve thus closing it it off. So, no vacuum,... valve open. Vacuum... valve closed.

Are you saying that heat comes out of the center vents no matter what selection is selected on the climate panel?.. defrost/no defrost? closing the slider on the center vents?

Thanks for the quick response! Yes, there is heat at all times no matter what selection is selected; also it doesn't matter if in defrost no defrost, slider position of center vent, etc. All I ever have is hot air.

Rick

Will the temperature of the hot air get cooler when selecting a lower temperature? Meaning con you confirm the temperature knob is commanding temperature changes? Temperature changes are done with flapper doors as the heated air exits the heater core. Because hot water runs through the heater core at all times (except when AC is selected), flapper doors control the heat output to the various exit outlets, floor, defrost and center. In full Defrost, you should hear the doors move from floor outlet to window defrost outlet. It is slow to move so be patient. De-selecting Defrost should port the hot air back down to the floor (default position). Demist; a little hot air goes to the windshield defrost. Center vents, slide to left, full hot air at vents, slide to right mix of cooler air.
Right selection knob; Off at 6 o'clock, Low at 7 o'clock. Med (Auto Fan) at 9 o'clock. High at 10 o"clock(not auto). 1200 o'clock defrost (full hot, high fan and auto opening of defrost to windshield, closing of floor.)
Does your AC work? Can you confirm the heater valve closes when you select AC?

I have diagnostic info for the AC if you PM with your email I will email them to you. For some reason I can not attach them to this post.

May I request same documents for the climate Control for my 95 conv? Thanks. What system do the facelift models have. I found an old doc for a Delaniar but not sure if that is used on the the 95 or face-lift years.

warrjon, my email is rblassiter@cableone.net in the USA if that matters. Thanks fpr the help and info!
Rick

Climate control
 

warrjon, my email is rblassiter@cableone in the USA. Thanks for your help and info!!

Rick

All XJS models after 87 used the Delanair Mk3. There was an update an for MY94 covered in one of the docs I sent you

That's not quite the complete picture. The valve is only closed if full cooling is required - if the temperature is in regulation, even with A/C on, the valve is open to allow warm air to be blended with cold air to achieve the desired temperature.

Ah, ok, gotcha...thanks for the correction. That makes sense. Is there no "econ" where cooler temp is achieved from the cooler outside air rather than engaging the AC clutch for regulation. Also, I thought just stopping the AC will "warm" the interior air rather than have to introduce actual heat to make it warmer if it's too cool during climate regulation.

I know that late cars had some revised controls including, I think, an 'econ' setting (or similar wording) that cuts out the compressor

But in normal/full operating mode the idea is to refrigerate all incoming air first and then heat it as needed. This is done to dehumidify the air. That's why you don't see Jags driving around with fogged-up windows :)

Cheers
DD

Fr. Rick again. I am afraid that I gave you the wrong email address. The correct one is richardlassiter@cableone.net in USA. Please send the info via this address and I am so sorry for the confusion.

Let me upload today. Here are the docs

With the '94, you should have the AC ON button at the top left--I assume you've tried that. And I assume you've checked for refrigerant in the system. What could be happening, and happens sometimes with my '92 (same basic Delanair Mk III) is that the aircon compressor clutch doesn't engage. I've found in that case, either turning the system off then on, or even better, turning it to full defrost then back to cold, kicks in the clutch. A weakening magnet is apparently the cause, if I remember rightly.
Doubtless one of the actual experts will chime in to tell you I'm quite wrong, but it does sound similar to my issue.

Didn't realise you had a 4-litre, but glad you got it sorted. Sounds like you tried something different, but hey, it worked.