Edited on 2007-04-11 22:53:58

I have a 1987 XJS with the V12 engine that has a baffling, at least to me, condition with the climate control. If the car has sat unused for at least 24 hours and I select "Heat" after engine warm-up, I get heat. So far, so good. The odd part comes in when after getting heat from the unit I turn the temperature selector to a point below ambient temperature or the temperature selector is below ambient to begin with. What happens? No heat.

It doesn't seem to matter whether I have the climate control in auto or manual mode. I've tried turning off the car for a short time hoping the electronics would reset but this doesn't seem to help and I've had some chilly drives this winter because of this. However, if I let the car sit a full day or more, I can get heat and lots of it so long as I don't do either of the above. Any ideas?

Any and all advice would be greatly appreciated.

Al

Submitted by rrudy2@charter.net on Fri, 04/13/2007 - 09:53

Hi Maynard and thank you for responding. Actually, what you describe is what should be happening but isn't. Lord knows, I'd be tickled if it was. I should have been a bit more descriptive in expressing myself. Sorry.

What is happening is, upon engine warm-up, I select, say, 75 degrees when the interior temperature is below 75 degrees and I get warm air. But if I move the temperature selector to any point below the ambient/interior temperature, whether the heat was on for five seconds or five hours, all I will get is cold air from that point on until the car has a chance to sit unused for 24 hours. There is no getting the heat back regardless of how high the temperature setting or how low the interior temperature. I have had the temperature selector cranked up to 85 and could almost see my breath inside the car and still no heat after an hour's drive. It made no difference whether the system was in auto or manual mode.

The interesting part is that cooling the car's interior in warm weather does not seem to be a problem. It's just the heating side of the equation that's lacking. Hmmmm. But as I live in the sunny south, I'll take a functioning AC unit over a working heater any day!

Al

Submitted by mghirsch@netzero.net on Thu, 04/12/2007 - 22:57

Unless I'm missing something, it sounds as if the unit is working properly.
In auto mode, the unit senses the ambient (in the car) temp and supplies hot or cold air as needed to reach the set point, and then maintains that temp.

In manual mode, it discharges air at the set temp.

SO if you start out with the temp set at 75, in auto, and ambient is 40, warm air will be discharged until the ambient is 75. Then it will discharge 75 air, altering the temp as needed to maintain 75. If you drop the setpoint to 60, cold air will come out until the ambient is 60.

If it in manual, the discharge air is what you've set it at. It doesn't matter what the outside or inside temp is.

Maynard Hirsch
94 XJS v12 Coupe
86 XJ6
91 XJS (RIP)
78 MGB
67MGB