What is a pentiometer ?I have also noticed when I initially start the auto none of the fan blowers work except “defrost”. After awhile the fans work at all various levels .
Wes,
i have not successfully found a replacement feedback pot that meets all the necessary criteria. Your only options for a failed feedback pot is either a reconditioned servo, or going to a manual control bypassing the amplifer and the sensing system.
Testing is simple if you have a volt meter and 9 volt battery with clip leads. If you message me…we can setup a time that i can call and walk you thru it if you like.
Cheers
Gary
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Wes,
There is a hot water temp switch which will prevent the system from blowing “unwarmed” air on the occupants until the engine has warmed sufficently in heating mode. The switch is located on the hot water pipes on the left side of the heater box.
Cheers,
Gary
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The potentiometer is a variable resistor, Wes - in this case with a ‘centre’ lead…
If the AC system is in ‘heating’ mode, the fans will not work until coolant temps reaches some 41C…
The servo is turned to heating mode if the cabin temp is below the set temp - or if the fans do not work until the coolant is warmed up; the servo is in the heating mode…
Frank
xj6 85 Sov Europe (UK/NZ)
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Good morning everyone from New York;
Another day of peculiar occurences. I did as suggested and set dial to auto.I then proceeded to turn heater control dial to 65degrees flap on center dash opened .I then immediately set dial to 85degrees the center dash flap closed .I did this about 15 times and each time it worked properly.I had hot heat for about 2 hours while driving.Suddenly the flap decided to open and I was back to cold air. The procedure performed the other day that was successful " flap opening and closing" based on temp dial does not perform as it did .The flap remains in open position and only closes when ignition is turned off.
Wes,
The center flap is vacuum controlled via a vacuum switch located in the Servo. Based upon your description of symptoms…you either have a bad/intermittent amplifer or a bad feedback pot. Depending on ambient temperature, you may remain in full heat mode for a period of time until the in-car temperature rises enough to require action from the amplifier to rotate the servo to adjust flaps or change fan speed. The amplifer either gets a bad signal from the feedback pot causing it to go to full cold or the amplifier has a failed internal circuit.
I have had used amplifers that appeared to be bad…dropped on the floor and then worked for a short period of time. Used amplifiers are a risk…they are still 30-40 years old and do not last forever.
Cheers
Gary
Hello Gary;
Thank you once again. Can this “feedback pot be purchased? Where is it located?If nothing works could I just prevent 'flap” from opening ,so I could have constant heat? Does this make any sense to you?
Regards;
Wes
Wes,
The feedback pot is attached to the end of the servo camshaft. There is not currently a direct replacement. You would need to obtain a used servo with a good feedback pot. While it looks easy…I dont recommend moving a fb pot from one servo to another as they are " clocked" and putting a fb pot in the wrong position can strip the servo gears ( dont ask how i know).
The other option is to install a manul control to bypass the entire sensing system.
Jagaur AC sensing system parts including refurbished servos are available at www.Jag-Aire.com
Wes…please dont just throw money buying parts at this problem. The feedback pot test is quite easy to perform and reveals alot about the condition of your system. You can pick up a cheap harbor freight multi meter/ volt meter and i can talk you thru the testing in less than 15 minutes. At that point you will definitely now where your problem lies and then you can make an informed decision about which route you want to take to get control of your system.
You can message me by clicking on the user icon at the top of the post then click message. I would be happy to talk you through the testing.
Cheers
Gary
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Hello Gary ;That Jaguar website is wonderful I looked at the manual control that fits into ashtray model# MC-17 it appears that will remedy the problem of heat .I temporarily prevented the flap from opening .I have hot heat coming from foot vents and defrost and rear passenger vents. It wants to open as soon as I lower the temp from 85 but it is sealed shut. At least I have heat until such time I look into manual control. I will wait until summer and look into the air conditioning problem.
Thank You very much for all you have done for me. It is greatly appreciated.
Regards
Wes
Wes,
Really sorry to hear that the replacement A/C Amplifier didn’t solve your problem…
Was this Amp new from JagAir or a second hand used unit?
Before you get any deeper I think you must be certain that your A/C Amp is working ok.
I had the exact same symptoms… changed the Amp twice until I found a used one that worked…
As Gary suggests the feedback pot would be the next on the list…
An other possibility could be the Temp sensor (located in a whole above the glove compartment on the underside of the fascia) even though it’s not known to fail…
Best,
Aristides
Aristides;
Thank you for your suggestions. I have printed all information I have received from various helpful persons ,yours included. I am doing what I had stated in my last post.At least, for now, I have heat for the upcoming winter in New York
Regards
Wes
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This of course the standard symptom of an AC amplifier fault, Wes…
…but it is somewhat crude - adding that with two amps showing the same; Gary’s point is certainly relevant. However, it is also relevant that during driving, when the temperature is reached, the fan speeds drops to ‘low’ - and the centre vents are partially open, blowing ‘heated’ air.
An alternative is some problem with the in-car temp sensor. The normal reaction of this system is full heat until the temp sensor signals that the set temp is reached. The servo then resets to ‘blend’ position, and the fans’ speed drops to low - and the main regulation to maintain the set temp is to change the fan speeds. If the system does not behave like this; something is wrong - but it is important that the overall system function is assessed this way; it ay clarify the problem…
The feed-back pot is certainly under suspicion, and should be checked out with procedures described earlier…
The in-car temp sensor is connected by a vacuum hose to the blower casing - cabin air is drawn through the sensor to keep it at cabin air temps. If the vacuum connection is disconnected, or the sensor is heated up one way or another; the AC amp will order the system to ‘cold’. One test of the sensor is to apply heat, cigarette lighter, at the sensor aperture - triggering the system to full cold. Cooling the sensor is a bit more difficult, one would expect the constant cooling of the system is full cold should have some effect…
Taking the car to a professional is viable, but few have the knowledge to sort of this particular problem quickly. It’s advisable that you do whatever you can yourself first - at limited cost…
Frank
xj6 85 Sov Europe (UK/NZ)
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Wes,
An other possible temporary fix:
When the system is on full heat just disconnect the AC Amp and the servo will remain in that seting forever and ever !!
Best,
Aristides
Maybe this could interest you Wes:
Also, in case you haven’t downloaded already, Kirby’s Book XJS Help has a very detailed description and troubleshooting info for the Delanair MKII system.