Hey everyone, I’ve been trying to get my 1985 jaguar xj6 VDP to blow cold air but will not move the Servos or turn the Compressor on, I have replaced all of the fuses, blower relay (blowers weren’t working either), and AC amplifier. The system has been charged with R134a. At the thermal fuse all connectors are showing ground and I can apply power to engage the clutch. Servo does not respond when I move either knob right now although the blowers do work in all positions. I did have the system turned on and servos moving before I charged the system. Is there anything else that could cause the compressor to not kit on?

 

To clarify, all four glass fuses?


If the system was previously low on freon the thermal fuse/thermal limiter is probably blown. Did you replace it when the system was charged?


The Ranco thermostat is in the compressor circuit. Make sure it is connected. And... it can be bypassed to test the rest of the system.

As for the control side of the system, check the temp switch under the dash that is attached to the heater inlet pipe. Actually, just unplug it and jump wires together. Does the system come back to life?

(There are two gray wires behind the console LH cheek panel that can be jumpered together that accomplish the same test)

Cheers
DD

 

I have replaced the four glass fuses. The two in the fuse box and each one behind the check panels.

I did switch the thermal fuse out after charging the system but wasn’t sure on how to see if the other had blown, is there anyway to tell?

I have looked at the temp switch and but have not tried jumping them together yet. I’ll do that when I get home.

I’ve heard of the Ranco thermostat but haven’t been able to find it. Where is it located? What does it do?

 

When I jump the thermostat and temp switch I can get the ac to turn on but takes a few minutes and I cannot switch back to heat with them jumped. When I turn the blower knob doors move like they should but the temp does not change. When I turn the temp knob the blend doors do not move. Could this be vacuum related?

 

To clarify, the compressor engages and the system blows cold air?

If so, the cold air is coming from which vents?




Some of the flaps/doors are vacuum operated, yes. To begin with, check the vacuum hoses that enter the cabin on the RH side of the firewall...below and slightly inboard of the battery, roughly speaking. One is a supply hose for the controls and the other goes to the heater valve.

I have a feeling that you might have 2 or 3 different faults at play here. We might be able to narrow things down

Put the fan control on low speed to minimize noise and then slowly turn the temp control from full hot to full cold. You should hear a slight whirring......which, from what I gather, you already do.

At full cold the center dash vent (vac controlled) should open and most the air should come from that vent. It opens on when max cooling is needed. Does it?

In full heat mode most of the air comes from the footwell vents. In blend mode mode most the air comes from the LH and RH dash vents. Is this happeneing?

In defrost mode most the air comes from the defroster outlets (vac operated) and the system defaults to max heat and max fan speed. Does it?

Have a helper turn the temp dial while you watch the heater valve in the engine bay. It has an external actuator lever so you can watch the movement. The valve should be open (no vacuum applied) in all modes except full cooling. Is the valve working?


Cheers
DD

 

Yes, if jump both I can get cold air to blow out of the middle vent but very rarely. When I got the blend doors to blow cold I got air from the center dash vent, the side dash vents, and a little bit out of the lower vents

 

Turning the temp dial does not change make the servo move and opens the middle door very rarely, even with both of the sensors jumped. The compressor is not kicking on either but system is full of Freon. Blend doors that seem to be actuated by electronics are moving. It’s starting to sound like I have a vacuum issue... I did just put new vacuum lines in the entire engine bay. Before I did that the vacuum line that goes from the heater valve to the lower line that goes to the fire wall was missing.

 

Well, that's a problem, obviously.

And you already have a new amp.

You can test the servo with a 9 volt battery. Disconnect the servo from the harness at the round connector. Apply 9v negative to the purple wire and positive to the red wire. the servo should operate and go into heating mode. Reverse the polarity and it should turn to cooling mode. Does it?

(Don't let the servo operate in this test mode for more than a couple moments as you run the risk of over-rotating the mechanism)


You have an odd collection of symptoms. The ROM has several good pages of trouble-tree charts. Even better if you can get your hands on the Delanair MK II guidebook....which someone might have already posted in one of the sticky threads at the top of this section.

Carefully confirming that all vacuum hoses and connections are good, as well as wiring connections, is a good (but tedious) first step

Cheers
DD

 

When I did the test you told me the servo did move in both directions, but I have noticed that the temp switch does nothing, where would you start from there? Could it be the temp sensor in the car?