My 87 Jag XJ6 that I recently purchased does not produce any heat. The A/C otherwise seems to work fine. I was told by the previous owner that it was the amplifier but would like to make sure before placing an order for this part. My factory service manual indicates checking the P and PR leads at the servo for voltage variations. How do I locate these leads. Are they clearly marked on the servo or the amplifier? Any assistance anyone could give would be greatly appreciated. Thank you.

Gerald R. Fast
87 Jaguar XJ6 VDP

Submitted by fast@uwosh.edu on Tue, 10/11/2005 - 19:28

After conducting additional diagnostic tests as suggested by respondents to my request for assistance, it appeared that the amplifier could indeed be the culprit. I replaced it with a new one and my problem was solved. I now have heat and just in time as the weather has turned much colder. Thanks to everyone for their help in resolving this problem

Cheers,
Gerald R. Fast
87 Jaguar XJ6 VDP

Submitted by bonnettoboot@e… on Mon, 10/03/2005 - 20:31

It is most likely that the servo is (stuck) in the cold position, the only way I know of to move it is using the jaguar test box, find out if anyone in your area has one, I do but then i'm in Los Angeles
Jaguar affectionado and etc.

Submitted by jam@ispwest.com on Mon, 10/03/2005 - 17:23

1) one of the servo's microswitches, (electronics store), 2) there is a plastic black & white check valve in the same vacuum line, routed near the side of the battery, check that it is not stopped-up, 3) the vent flaps linkages out of adjustment, (serious work), 4) a faulty or disconnected thermo-switch on the driver's side, behind the center console, looking up from the floor, mounted in a brass tube, 5) a faulty Ranco Thermostat located on the passenger's side, behind center console, looking up and back from the floor, very hard to see. Best bet is to substitute the Servo or Amplifier and check for any difference. There is a Linkage Adjusting Schematic available, but that should be a last resort, best to look at the linkages as they move to see if anything is loose.

Submitted by fast@uwosh.edu on Mon, 10/03/2005 - 17:06

I worked on my Jaguar over the weekend and found that there is vacuum at the line connected to the heater valve and when the line is removed the valve does indeed move down. Thus, this part of the system seems fully operational. However, when I move the temperature selector to the highest temperature, the center vents do not close and cold air still blows out of these vents. It appears the servo is not moving from its 'cold' postion. What is your best bet as to the problem?

Gerald R. Fast
87 Jaguar XJ6 VDP

Submitted by fast@uwosh.edu on Wed, 09/28/2005 - 16:48

Thank you very much to Doug, William, and J.A.M. for their responses and excellent suggestions. I will follow up on these and let you know how it works out. I am a long time Jaguar enthusiast but new to the club. This is my first query in this forum and I am indeed impressed by the helpful and immediate responses to my problem. It is very much appreciated.

Gerald R. Fast
87 Jaguar XJ6 VDP

Submitted by bonnettoboot@e… on Tue, 09/27/2005 - 23:03

The AC may be working even if the servo and amplifier are bad, the system could be frozen in the cold position. To check, with the car running and the AC blowing out of the centre console, turn the temp control knob to 85, if all is well the servo should rotate and the centre console flap should close, air coming only from the dash sides and footwells. To check the heater valve with the car running and the AC on pull the vacuum hose off the heater valve, you should notice two things, there should be avacuum at the hose and, the valve should have moved down to the open position, often the valve just sticks and can be freed with judicious use of a long screwdriver. Jaguar affectionado and etc.

Submitted by jam@ispwest.com on Tue, 09/27/2005 - 21:18

yes, if the a/c is fine, then the Amp. and Servo are fine. most likely it is the water/heater valve, those can be bought for $20. on eBay. I don't know why everytime there is a climate control problem, the Servo or Amplifier are always diagnosed as the problem. I have owned my 1984 XJ-6 for 14 years and never had to replace the Servo or Amplifier, or any other electronic climate control component for that matter, except you guessed it, the water/heater valve. When I had problems with the blowers not accelerating to 4th speed, it turned out to be the ground wires at the blowers not making good contact, but I was told it was the large Relay on the driver's side, and again you guessed it, the Servo or Amplifier. but neither was bad, and this year the a/c has performed like a freezer, it gets so cold it has to be set at 75. Long live R-12, and if the Earth is warming up, it must be because of all the Atomic Bomb testing during the last 50 years, not because of R-12.

Submitted by dougdwyer@adel… on Tue, 09/27/2005 - 20:58

Amplifiers are common culprits but, if I may sugesst, make sure the heater valve is not seized before knocking yourself out on electrical diagnosis.

Doug Dwyer
Longview Washington USA
1987 XJ6 Ser III
1988 XJS V12 Coupe