Series III - Heat/AC Temperature Switch/Sensor Help (Stuck on Cold Temp)
 

Hello all,

I was hoping to get some diagnostic help but searching to forums turned up nothing under what I could think to look under so hopefully ya'll can get in point back in the right direction.

When I turn on the fans, no matter what my temperature dial is set to (coldest or hottest) the air comes out ice cold and ac compressor is engaging even when set to auto with temp set to 80. this is a very recent development but I haven't made any other changes to that system recently. less than 1 month ago it went from heat to ac making all the right moves (compress click and engage, middle flaps open and close with appropriate temp. settings, etc.)

edit: to be clear, my temperature dial is not physically 'stuck' on 60 degrees, rather, no matter what i set the dial to, the air comes out as cold as possible.

anyone have a similar experience and want to share?

thanks!
john cook.

First, it's normal for the compressor to engage even when heat is called for....so no worries there. The system is designed to refrigerate all air coming into the cabin first...to dehumidify it...and then heat it as needed.


What happens to air flow when you adjust the temp control? If the air flow changes from center dash vent to footwell vents as you turn the knob from cold to hot then you know the system at least understands the request for heat and is trying to comply.

Also, when you slowly turn the knob from cold to hot do you hear the sligt whir of the servo motor? You should.

Can you get hot air if you select 'defrost'?

When you move the temp control from cold to hot does the heater valve open and close? You can watch the little operating arm on the valve move back-n-forth. It might be stuck 'closed'....preventing hot coolant from flowing into the heater core.

Next, turn the control to the hottest setting and then remove the vacuum hose from the heater valve. You shoud NOT feel vacuum if you put your thumb over the end of the hose. The system uses vacuum to close the valve.

Cheers
DD

Doug:

Thanks for the reply!

Didn't realize compressor always kicks on upon turning system on - good to know!

Air flow does change when the temp. dial is moved from the center vents to the footwells.

When I turn the knob from cold to hot slowly I do hear a small click and whirr once the temp dial reaches a certain number.

I do not get hot air from any vents on defrost mode. It's still blowing fully cold refrigerated AC air around 60deg.F.

I only had time to do interior testing this morning - will post results of the heater valve and vacuum test tonight and post results in case that doesn't give me an obvious answer to this problem.

Just tried it again - this time, center vents did not close and floor vents did not open.

pulled the vacuum line and there IS vaccuum even when set to high and auto with temp on the highest setting.

Center vent is closed by vacuum switch in servo (red line). Is heater valve open. It also is closed by a vacuum switch in sevo(black line).

no the heater valve is closed because when I have the settings on that should request heat (80degrees and high, auto, and defrost) there IS vacuum suction on the black vac. line going to the top of the heater valve 'bell'.

So presumably this means that there is not a mechanical failing of the heater valve (necessarily, at least) but rather something electrical up the line in the switch/control system which it not sending the appropriate commands?

although, even with the vac. line removed and the settings on high and 80, there was no heat coming in, just cold a/c air.

To clarify, does the heater valve actually open, I.e. Is the arm on it in the down position and is the rubber hose on the outboard side get hot.

NO, no !

When HEAT is called for there should NOT be vacuum to the heater valve. Vacuum holds the valve closed for max cooling.

For heating, vacuum is *removed* and the valve should *open*.




Which suggests that A) the incoming air is not being directed thru the heater core or B) incoming air is going thru the heater core but there is not hot coolant entering the heater core.

If "A" the air directing flaps are stuck, broken, or are not being properly commanded. This could be a mechanical fault or a electronid control problem.

To check for "B"......

With the heater valve *verified as open* are both heater hoses getting hot? If "yes", then that suggests that hot coolant IS flowing thru the heater core. Good!

If 'no', that suggests that the heater core is clogged....or:

In some rare cases the heater valve looks like it is open, judging from the position of the little operating lever....but in fact is stuck closed. The actual valve inside has parted company from the external operating lever.

Do you have the Delanair Mk II manual?

Cheeers
DD

Hey Everyone, thanks for the assistance in diagnosis but it's about to get even trickier:

so this morning I turn on car usual symptoms (cold air on all settings) but about 10 minutes into driving, there was an immediate change from ice cold to heater-hot. stayed blowing hot for about 15 minutes.

I parked but left the car on and running but turned off climate control settings. Then turned them back on and it was nothing but cold AC air again. Left it on for ten minutes while driving again but this time it seems to be stuck on cold/AC again indefinitely.

Doug, I know there is not supposed to be vacuum on the 80, high setting going to the heater valve but there was vacuum pulling (even though there's not supposed to be). So I suppose that fact puts me to your A or B split which I will investigate this afternoon.

I don't have the Mk II Delanair manual though I imagine it would be widely helpful - the jaguar service manual covers some of the material but the drawings are greyscale and very few and far between. Anyone have a scanned or digital copy available? I'd be glad to roll it in with the jag manuals I've posted on these forums to try to condense the downloads needed.

The heater valve is closed by the servo only.period. Otherwise it's open.. There is a black vacuum line exiting the servo that goes to the heater valve to open it.There is a a vacuum switch in the servo which applies vacuum to the heater valve when servo is in proper position, which is only in full (or near full) cooling. Otherwise no outgoing vacuum and heater valve remains open.
Now, servo position is controlled by the amplifier which receives signals from 2 in car sensors.

I would leave the vacuum line disconnected from the heater valve and drive that way for a while and see if you have heat when needed. That will help pinpoint the area to look at.

This is an excellent thread for people like me who are ignorant of the workings of the climate control system. Once John resolves his problem it would be great sticky material.

The answer to this issue is simple and the clue to diagnosis was given in John Cook's last posting: the system is oscillating between hot and cold. This is the CLASSIC sign of the failed AC amplifier - located in the driver's side (LHD) of the console. Cure: replace the amplifier by a more modern unit, easily (but not cheaply) available. You simply leave the original unit in place and the much smaller and better new unit is connected and tucked alongside. The new units are available from the usual suppliers of Jaguar parts.

THank you to everyone - the frequency with which my system wants to oscillate between heat (as settings are correct for) and cold AC (the opposite of what I want) leads to believe the Gregory has hit the nail on the head with the AC amp. The change is so immediate that the non-mechanically inclined passenger immediately asks 'what happened' because the system goes from hot heat to ice AC immediately.

Will be looking into the new AC amp as well as an LED replacement for the map light that blew on my Thanksgiving drive from Texas to Tulsa, OK. At least the machine made the travels mechanically safe and sound (even if I had to wear a coat inside the cabin the whole way). Will source and price part and post results of installation of new amplifier.

As if I needed to really check,

Welsch doesn't have it.
JagBits wants 350 for used, untested original model.
David at everydayxj has a used, untested ac amp for series III for 60$
Jaguar XJ6 XJS Air Conditioning Amplifier - C45402 AAU5688 AAU3668 RTC671

Can't find a source for the newer replacement part yet - anyone have any leads there? I know John's Cars up in Dallas is rumored to have had them at one point. If I finish class early enough, I'll give them a call and check availability.

Every used part that Jagbits sells has been tested and comes with a 6 month replacement warranty. We actually test every used part before we ship it, if it doesn't work we don't ship it. If you can buy one used that works for $60.00 I would buy it for sure. Let me know how it works out!

Did you try XKs Unlimited? Coventry West?....

Gary at JagBits - Sorry I completely misread the testing status and warranty situation with the parts you provide - that is fantastic and would really help with diagnostics knowing I had a good unit. I wouldn't want to misrepresent your offerings and I don't mean to sound derisive of any of these options - I'm very enthusiastic that with this model we are still in such a great position to have so many good suppliers.

None at XKUnlimited neither the old nor the upgraded modern replacement to which Gregory referred above. Coventry West has a page up for it but priced at $792.00 which says they are also out of stock. I couldn't find any mention of an upgraded/superior modern replacement on any of these usual supplier websites.

jagbits
 

No problem John I just happened to be reading this thread and wanted to clarify our used parts policy. I am here if anyone needs me!!

John,

Did the AC Amp solve your issue? My Jag has the exact same symptoms.

Thanks!