Hello All,

The subject pretty much says it, but there are a couple of details I'd like to offer in hopes that it will greatly narrow the possible causes.

This past weekend I suddenly had no heat from the climate control in my car (1999 XJ8L). Everything had been working perfectly normally then, *poof*: no heat. My suspicion is that the heater tap has stuck in the closed position.

You can definitely tell that the AC compressor is still running to do its dehumidification thing since the air coming out of the vents is far colder than the ambient air temperature outside.

Since the heat disappearance there has been one instance where things went back to normal, briefly. I've been doing test turn on/offs of the system to see if this is intermittent or consistent, and with that one exception it's consistent.

From what I've read so far in JTIS it seems that the heater tap should be reset to full open when the system is shut down and/or the car is turned off. This is clearly not happening.

Any guidance on fault diagnosis and/or repair would be much appreciated.

Submitted by vogelbp@gmail.com on Wed, 08/29/2012 - 19:36

Hello All,

Life has thrown a number of other more critical issues my way, so this one went on the back burner, particularly during the summer. However, I know that winter is eventually coming and I'll need to get this fixed.

I now believe it's probably the auxiliary heat water pump. We had a very odd cool snap here in Virginia about 2 weeks ago and one morning, with the thermostat set on 78 degrees, I suddenly had heat again. I'm all too familiar with intermittent failures and "miraculous" (and temporary) healings of same.

If anyone has specific advice or knows of sources of photographic documentation on doing this job I'd really appreciate being pointed in that direction/those directions.

Also, do these cars have any quirks/eccentricities as far as refilling the cooling system? I'd imagine that I'm going to need to drain the entire system (whether by intention or simply by opening up something that allows it to dump all its coolant). I've worked on some cars where you had to go through "burping" rituals to get potential air locks out and others where there was nothing more complex than pouring in new coolant.

Thanks in advance for your assistance.

Submitted by NE40-48370 on Wed, 02/08/2012 - 06:04

Do an archive search of the X300 forum on Jag-Lovers if it hasn't been covered here before (I'm a newbie on the JCNA forums). There will be lots of photos etc on the J-L forum.

The pump is a six iby two inch black capsule shape, with two hose connections only at the rear end down on the left side inner fender. It is near the valve block but that looks very different and has more hose connections IIRC. On RHD cars where the servo is on the opposite side, it is accessible once you remove some underbonnet trim on the left side and loosen the header tank to lift it out of the way (no need to disconnect more than the two small hoses clipped into their fittings up top. at the front of the tank). NB: DO NOT mix them up on replacement, which is easy to do but will give you puking and overheating trouble. Well, the car, not you exactly. Mebbe both? :-)

The pump is held by a black steel bracket on two 10mm set screws IIRC and one of the hoses comes undone easily the other needs a bit of fiddling to get good access. Once the clips are loosened they should slide off OK as the pump housing is plastic so no rust., Unplug the short pigtail and you can work on it one the becnh. Even if you just attend to the electrical side, it is worth inspecting the pump side as there can be end-thrust wear on the metal bits. A new pump is the answer if you intend to keep the car long term but a patch is worth trying if the price of a new pump is high where you are. The pump runs even when no heat is being called for, so long as the ignition is on and the climate control is on IIRC, hence it eventually wears out.

If you can afford to take a couple of weeks fixing it then your weather is not as cold as it is here! The car is freezing with a dud pump.

Submitted by vogelbp@gmail.com on Tue, 02/07/2012 - 21:30

Edited on 2012-02-07 21:31:56

Peter,

Thanks for your input. I'll have to see about locating the various components over the next couple of weeks. It sounds like this is going to be a lot of detective work.

Submitted by NE40-48370 on Tue, 02/07/2012 - 09:36

Morel ikely to be the pump IMHO. Common fualt after ten yearso r so as it runs the whole time the cliamte control is on. Feel for a fiant buzzing. Access is not too bad on RHD cars but may be trickier on LHD. I fixed my DIY be cleaning up the commutator and putting new brushes in adapted to fit from something else (just take the remains to a motor shop.). I laos bought a used one from ap lace that gave some kind of warranty but in the end that was useless because two yearsl ater my fix is still doing fine.

Thep ump part can be separate dfrom the omtor part but it is easier to disconnect both hoses and take it out complete with bracket and split it on the bench.

Peter the Heater