Hi,
While out with my wife for a drive up the Central Coast of California last Saturday evening, after the sun went down and the fog came in she requested to put a bit of heat on, as opposed to putting up the hood. As I attempted to comply, all that came was cold (A/C Cold) air, Any combination of settings, brought only cold air, higher setting (90 degrees F) brought more and colder air.

Have not had any problem previously, though I did notice once that upon pulling over at a mountain summit the A/C would stop blowing cold and provide hot air for a few minutes, then revert to normal operation.

From these, I suspect a fault with the doors/shutters in the ventilation system, but don't have a clue how to proceed with troubleshooting. Any suggestions would be welcomed, thanks in advance.

All the best,

Jerry Lippmann
1999 XK8 BRG (134Kmi)

 

Jerry, the fact it stopped blowing cold air when you stopped is concerning - when the temp approaches overheating it will disable the ac. Was the factory temp needle rising at the time?

I saw this in my 98 when the factory mounted defective coolant pump started to fail. Forward motion provided enough air flow to prevent overheating, but idle = watch temp rise & ac turn off.

Not trying to scare you, just be aware. 1999 may be close enough to the 97 98 run of defective pumps IMO.

This has nothing to do with your primary question though.

John

 

Jerry, here's the link to the climate test procedure.https://www.jaguarforums.com/forum/x...t=Climate+test

John

 

Chances are, the problem is with the (electrical) auxiliary heater pump (separate pump that circulates water in the heater core). Get the electrical manual from jagrepair.com, find (and check) the fuse, and then use the relay connections to test the pump. If you have high resistance, chances are the pump brushes are worn out (open circuit), and can be replaced inexpensively (but the pump is a bear to reach). If the resistance is fine, then you can supply voltage to the pump (from the same relay location with a jumper wire) and check if you can hear the pump (very faint, engine must be off, use a mechanic's stethoscope on the pump body).

Another test is to unplug the water valve (plug is on the firewall). The pump defaults open, so you should have plenty of heat at all times with it unplugged.

If you have a laser thermometer, you can trace the temp of the various hoses and try and figure out where the heat stops, but it is less obvious than it seems.

Last (or first!), coolant seem to form a film deposit over time, and prevents good heat transfer. You might have to do a simple heater core flush and cleanup (radiator cleaning solution works great) to restore good heat transfer. After a ton of research on my own car, the no-heat problem I had ended up being cured (and then some) with a simple heater core cleanup. Could not believe the difference. I used the (inexpensive) garden hose technique, with a short clear tube and adapters from the hardware store, nothing complicated. Now, even in winter, I have some heat in the car less than a mile from home. The idea here is that doing this core flush is a lot less pain than getting that pump out, and so needs to be tried early in the process.

Best of luck, keep us posted.

 

Hi,

Thanks for the guidance, I'll have some time to diagnose over the upcoming long weekend and will report.

All the best,

Jerry

 

One of the most “rewarding” issues with our xk8’s. s/ So, with zero heat, and having read most all threads regarding this problem, thought I would attempt troubleshooting on a scale from easiest to hardest...

1. Check aux. coolant pump fuse. It’s fine.
2. Swap relay, just in case there was a problem there. No change, still no heat.
3. Check hoses into and out of heater core. The top hose, designed with a slightly crimped fold is ok and not collapsed.
4. Unplugged the heater valve, hoping to have heat as fmertz suggested there should be ample heat since the valve defaults to open. Result: still no heat.

Knowing this, would the valve be the problem? Yes, the issue with worn brushes in the pump is well known, but I’m trying to identify the other possible problems before doing the pump removal and repair/replacement. I don’t have some of the diagnostic tools others have mentioned to pinpoint hose temps, voltages and the like...just my hands and brain.

Any and all thoughts welcome.

 

I had the same experience as fmertz, above - clogged heater core. I had a cheap mechanics stethoscope and found that the aux heater pump sounded like it was running, so I took to flushing out the heater core by way of the two hoses on the firewall that connect to the heater core. I did get a hose clamp removal tool and long hose pliers for not a lot of money, because getting to these hoses and getting them free of the heater core pipes is a job. But once I got them off I connected up some 5/8" heater hose and used compressed air to blow out the core, and sure enough it was clogged with crap. I ran some cleaner thru it, some water, then some Dexcool, and now I'm good. It is a pain, and I learned how to get the header tank off and on within minutes after a lot of practice. But in the end it was worth it. Also, be careful with the hose pliers. I managed to slightly mangle one of the heater core pipes, but fortunately, not enough to cause a leak. I think the problem was probably caused by a previous owner mixing coolant types or using a stop leak, both of which are not uncommon. Oh yeah, be careful with the low coolant sensor on the bottom of the header tank too. I found it easier to lever it out (it snaps in place) than to try and get the electrical connector off - hate those things !