Hey guys,

Just bought a 1989 XJS, in great shape. But I had to drive it home in 20-degree weather last night thanks to no heat. That's because whenever I turn the HVAC system on, no matter the setting, the compressor kicks on immediately and the car goes to max cool. I can tell the heater core is OK, because if I shut everything off, heated air will leak in around the windscreen vents. But as soon as I kick on the system, I get full cold.

The rheostat for the temperature control feels a bit "loose," looser than in any other XJ I've had. Any ideas on where to start?

Jess

 

Normal for the compressor to kick in whenever the system is on, even when heating is called for. The system is designed to refrigerate all the air first for dehumidification...then heat it as needed.

First question: when you dial in max heat on the control knob does the air flow switch to the footwell vents? If so, the system at least understands that you are asking for heat and is trying to comply.

Cheers
DD

 

The compressor is designed to run in all settings if I'm not mistaken hot/cold/defrost. You may have a blend door not working which is not allowing for air to enter the heat matrix/core. I'm STILL trying to sort my 86 some 3 years later, luckily I live in NE Florida and don't need much heat.

 

When I dialed to max heat, the system did start trying to send air to different places. Even after 5-10 minutes running, though, the air was still cold.

And I believe air is coming out from all vents anyway ... so it would seem I may have blend door issues.

I almost hate to ask the follow-up question -- how hard are those to get to?

Jess

 

Good that the system is at least trying to work.

Before taking anything apart trace out all the connectors for the system (there will be 6 or 7 of them.... tiny wires and tiny connectors....you'll see) and clean them. A couple are hard to reach....way up high on on the left side of the climate control case.

I've turned a couple of these systems from "sorta working" to "fully operational" by simply cleaning the connections. Clean the grounds, too......one on each side of the climate control case on the vertical dashboard support braces.

Cheers
DD

 

Is the heater valve working? This is a very common, cheap and easy solution to many XJ-S no-heat issues.

 

The XJS.
Too hot.
Too cold.
Only Jaguar could come up with a vehicle that could simultaneously boil it's engine whilst freezing it's occupants.
Long may they reign.

 

Here's a neat follow-up, never had this happen on a car before...

The system is operating ... backwards.

It is sending hot air to the defrost vents, while sending ice-cold air blasting out of the floor vents. So instead of warming my feet and cooling/defrosting the windshield, it is doing exactly the opposite. This has the side effect of fogging the windshield pretty badly after the car is shut off (i.e., condensation as warm air continues to waft into the cabin).

However, if I set the system to around 75 degrees and put it in Auto mode, it will at least not send ice-cold air to the floor vents. It sends cool air then, but not COLD air.

This is progress, I must admit, as initially it would blast cold air out of everything. I'm at least getting some hot air now, although the car doesn't have a clue where to send it.

If I operate the system in ANY mode other than exactly as I described above, I either get hot to the defroster and cold to the legs, or cold to both places.

At least the system is trying. It is properly sending correctly-tempered air out of the face vents. Basically, all I need it to do now is stop blasting my feet with cold air and we're good to go.

Jess