I need a little help understanding the climate control on my 86 XJ6. I have searched the forums and not found anything like the problem I am dealing with. This car has been sitting up for a couple years before I acquired it.

In the morning it's cool outside say about 50 degrees I get in the car and start it up. Thermostat set to 70 degrees. The Heat and the Blower's never come on. I turn it on the defroster and the blower comes on but no heat. As the day gets warmer all of a sudden the blower comes on and air conditioning starts up. Any ideas on where to start??

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in my 1984 the Heater does not blow hot air, or much air at all, and the blowers do not begin to run until the engine coolant is up to a certain temperature, takes about 10 minutes or so for the Heater to start; That's why I installed Front Seat Heaters, it takes 3 minutes for the seat and back to become warm enough. A Warm driver is a Safe driver, like SAAB says.

the a/c runs if the temperature is hot enough inside the car, the TEMP KNOB being at 65 degrees, and based in the Inside Temp Sensor located under the front edge of the dash pad, it can be felt in a direct line above the glovebox lock if you run your hand under the front edge of the dash pad, or use a mirror and flashlight to see it.

 

All you'd get is cold air so the system won't kick on until the engine has warmed up a bit. That delay is normal, intended operation. The engine doesn't have to be fully warmed up, just partially....enough to see the temp gauge needle start moving up.

However, if the system won't kick on at all when heat is called for, even with a warm engine, you probably have a defective heat sense switch on the heater core pipe.


Normal, as defrost/defog mode bypasses the 'automatic' temp sensing functions of the system

If the system is trying to *cool* the cabin it doesn't care about engine temperature. It'll kick on right away.

But, as Jose says, the system has to 'see' a large enough difference in cabin temp versus selected temp to work at all. It won't try to heat a cabin that's already at (let's say) 90ºF nor will it try to cool a cabin that already at (let's say) 45ºF.


Here's some more reading

https://www.jaguarforums.com/forum/x...basics-178058/


Cheers
DD

 

There is a temp switch on the heater core pipe. This is a surface contact switch and I believe its cycles at 80 or 90 degrees F. Simple and effective. The switch is only effective when the car is in heat mode. In a cooling mode the thermo switch is ignored and the fans will come on instantly.

Check your heater core pipes and valve and make sure you have water circulating sufficiently so the pipe gets warm enough to trip the switch.

If you remove the transmission tunnel triangle trim there will be two brown wires dangling. If you short them this simulates the thermo switch activation and I guess Jaguar put it there to assist in diagnosis.

If you are brave like me you can put a DMV meter on the ohm setting and use a bbq lighter to heat the switch and observe if it trips on when hot and off when it cools. The thermo switch can also be removed and bench tested.

 

This is great. Thanks guys. More info than l thought I would get. So I got heater core problem or a sensor problem. Where would the sensor be located??

 

The heat sensing switch is on one of the pipes to the heater core. remove the LH under-dash panel and look up, in the area above the parking brake handle, and you'll see the pipes and the switch.

But.....

I would first test the circuit to see if you're on the right track....and there's an easy way to do so. Click here and go to post #17....

https://www.jaguarforums.com/forum/x...basics-178058/


In post #17 there's a picture that shows two wires with light gray connectors dangling down on the carpet. These are test leads for the heat sense switch. Jump these two leads together and see if the system comes to life when heat is called for.

(For umpteen years I wondered what those wires were for...until ISC mentioned their purpose. Shows that there's always something new to learn, eh?)

Cheers
DD

 

wow, that is new to me too, I have seen those wires, always thought they were for the Vanden Plas gooseneck accessory lamp or some other accessory.