Here the cooler weather is here and my heater wont work! The fan works and the left knob turns but no heat. Any thoughts on what to look for??
Dick C.
1989 V12 XJS coupe

 

Could it be the heater control valve? May be stuck shut.

 

Could be a vacuum leak. That's what happened to mine

 

Lots of 'could be' possibilities

Heater valve stuck closed, as mentioned

Clogged heater core, or air pocket in heater core

Internal flaps not rotating to direct air thru the heater core



When you ask for maximum heat with the temp control knob does the system respond by directing air flow to the lower vents? it should, and it would indicate that the system at least understands the request for heat and is trying to comply.

When you select defrost do you get hot air from the windshield vents? If you can get hot air via this method then you know the heater valve and heater core are OK

Cheers
DD

 

Will check all these out, thanks guys!!

 

just a point of note

the heater valve is normally open with no vac , and the vac operates it for cooling


easy to test

turn on the engine, and set the car to cooling , then pull off the small vac pipe from the top of the valve, the valve should move while pulling on and off the vac pipe

BB

 

I'd put my money on the heater valve. Located on the firewall inside the engine bay. A good way to check is to warm the engine, remove the front LH side of the console and check the pipes for temperature, if they are cold then it's definitely the heater valve.

These can be replaced with a GM or Ford unit as long as it is NO with no vac. I used a GM unit and it works great, it is plastic and much lighter than the original so does not need to be bolted to the firewall. Mine is held in place with the hoses and has been there for 6 years now.

 

I should mention that the air conditioning compressor has been removed from the car, the PO said it 'froze up', I have purchased a used one but haven't installed it yet. Is that contributing to my problem?

 

No. In and of itself your lack of a compressor isn't the cause of the problem. It does, though, make one wonder what else the PO might've done to the system


Cheers
DD

 

Yes, the PO unfortuneatly is deceased, I bought the car as a 'parts car' but thanks to the people on this forum it is now my daily driver. Hopefully I can get the heater working as I plan on driving it some over the winter.


Dick C.