Hello all,

I have an 89 XJS that is only blowing cold air. I checked the heater valve and it is operational and has vaccum; also the hoses going to the heater valve have hot water going thru them. The heater worked great when I first purchased the car and was working fine when I got back from deployment a year later. The problem started (I think) after I had the car brought in to have the A/C charged. The A/C compressor was bad and needed to be replaced; now the A/C works great now. I didn't notice the heater didn't work as it was summer but now the car is here in Germany and I went to use the heater as the weather is turning a bit chilly and I find the heater blows as cold as the A/C, I mean that literally, when I turn on the heater its no different then when the A/C is on. Any ideas where I should go with this issue at this point?

Thanks in advance!

Kevin

 

Can you hear the servo motor whirring when you move the temp knob? On my car it's pretty noticeable, I know exactly when it's trying to stabilize even when driving.

I highly recommend picking up the climate control manual from eBay or a vendor, they're like $15-$20 and look like they were drawn by my 8-year-old, but give you HIGHLY specific troubleshooting instructions that are ridiculously easy to follow.

 

When listening for the "whirring" should I have someone turning the temp knob from cold to warm while I'm listening with the bonnet up? Also, is it better to have the engine running or simply have ignition on?

Thanks in advance for the advise/assistance.

Kevin

 

This is all inside the car. Just turn the system to auto and adjust the temp knob from one extreme to the other. Give it a few seconds on either end. You should hear an electric motor whir from the vicinity of the temp control knobs. Some guye recommend pulling the fuses from the electric fans to be able to hear it better, you can try that but I can hear mine while driving with the system in auto even with the radio at a reasonable volume.

If you hear the whir, your amp is OK and it's more than likely a vacuum issue to the heater blend flaps or perhaps a mechanical issue (flap jammed, actuator broken). If you never hear the servo, either the amp is bad (very likely) or the servo is bad (not very likely). Listen for the motor and report back, if you're not hearing it then we can start troubleshooting with a voltmeter. Even if the amp is bad, we can "force" heat on by jumpering a few terminals - you won't be able to turn it off, though.

 

Hold everything ! :-)

An '89 XJS will have the Delaniar Mk III system. It doesn't have a servo like the older Mark II system so there won't be a "servo whir" to listen for.

Cheers
DD

 

So, to clarify, besides having cold air when you want hot, the air flow doesn't change to the footwell outlets?

If the air flow diverts to the lower vents then we know that the system at least recognizes the request for hot air and is trying to comply.

The "could be" list is very long but I've fixed a couple of these system by spending a couple hours cleaning the tiny electrical connections (several on each side of the heater case....some hard to see and reach) and cleaning the main grounds (on the vertical metal supports on either side of the heater case)

Cheers
DD

 

Sorry, missed that! Thanks Doug!

 

Doug, I do get airflow to the footwell outlets. To me it seems as if the system is functioning but just doesn't "recognize" the change from the control to blow hot. The heater valve is functioning; has vaccum, the hoses going into the heater valve have hot water. when i initiate the system and have temp set to 85 there isn't any delay like you would expect with the system (waiting) to blow hot it just starts blowing cold.

 

Ok, good. That's half the battle towards a working heater




When heat is called for air is sent to the footwell vents so at least *that* part of the system knows you're asking for heat. It sounds like the flap that directs incoming air thru the heater core doesn't know you want heat. That's one of the flaps which is rotated by a little motor on the side of the heater case....can't remember which side, off hand. It's one of the devices with tiny connectors and tiny contact pins and tiny wires which corrode very easily.



Remember, the only time there should be vacuum at the heater valve is when cold air is being asked for. Vacuum closes the valve




Good





There's a bypass switch....which someone may have disconnected....which defeates the fans IF heat is called for the but engine isn't warm enough to provide hot coolant to the heater core. The switch is mounted on the inlet pipe to the heater core

Cheers
DD

 

Roger on the vaccum; there is only vaccum when the system is set to "cold". Where is the heater core/heater case located in the engine compartment? I have been trying to find a schematic of the XJS V12 for awhile with no luck and not being a mechanic im kinda "winging it".

 

By the way.....

If the usual routine checks don't give results I would strongly urge anyone having climate control problems to buy the appropriate manual. This is for the Mk III unit:

Jaguar #44 Delanair Mk 3 Air cond. manual fault diagnostic, Language: English, Category: Owners manuals


Here's one for the earlier Mk II system:

JAGUAR XJ6/XJ12/XJS CLIMATE CONTROL REPAIR MANUAL 74-87 | eBay

The easiest way to tell which unit you have is the temp control knob. The temp control knob on the Mk III system has a "pull out for manual control" feature. The Mk II system does not. The change took place circa 1987.

Cheers
DD

 

It's inside the dashboard.

Cheers
DD

 

The most likely cause is a partially stuck "flap valve" which is actually a drum rotated by a small servo situated on the RH side of the unit. Remove the trim with the vent on the RH side of the centre console in the RH foot well. Remove the air duct going to the vent. (Three small screws and a tab which is part of the duct, a bit of lift and twist at the inner end. Fiddly.) Then feel with your fingers and see if you can make the valve rotate 5 - 10 degrees. Switch on engine, move temp from full cooling to full heat to full cooling and back again with about 10 seconds between each operation. If no movement try to push a bit in this and that direction on the drum valve while changing cool/heat etc.

 

pm me with your email and I can send you some diags and info

 

Well, the whole issue with the heater blowing cold has been resolved. It wound up being dirty connections. took out the parts, WD40 and some cleaning, put it all back together and lo and behold.... Heat!

 

Hi Kevin,,, this is an old thread but I am having the same issue... Which connections did you clean. Maybe this will solve my issue as well...

Thanks in advance.

Gamy R.