Series 1 cold knob


I’ve a 1973 xj6 series 1. Any help appreciated.
Would anyone know the part number or name of the cold turn piece ( left of the radio) on the climate control box ?
The hot air has a metal pin that protrudes out (not wired) . But I removed the cover and there’s no corresponding unit for the cold dial on the left. It’s a 12a a/c car. Photos below.
Thank you.

If I’m understanding you correctly, you are missing everything behind the knob hole on the left of the radio? That is a thermostatic switch that controls the A/C system. It has an electrical component that operates the compressor and fans as well as a capillary tube that is in contact with the evaporator.

I doubt you will find new ones but the part numbers are BD.36823 for the thermostat and 12946 for the switch. If it is all missing your best bet would probably be to find a used one… You should also investigate why they are missing. I’ve seen people bypass the whole thing and try to use switches - forgoing the thermostatic capabilities of the system. Do you have any mysterious switches somewhere?


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Thank you very much.
You just resolved my confusion in 1 post :pray:
I’ll look for any mysterious switches.
I’ll get a searching.

David from Everyday XJ has the Thermostat and Switch Assembly BD36823.
Ordered. At a minimum I’ll have symmetry.

You’re welcome and welcome to the forum Omar. Looks like a pretty Series 1 you have there… Best of luck with it.

David at Everyday XJ is a great guy. Glad to hear he had one for you.

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Thanks Again Mike.
I found my XJ6 in Denver, with receipts & photos back to 1997 which is really nice to have.
Just need to figure out an air conditioning solution :slight_smile:

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Welcome to the world of Series 1 heating and cooling. The A/C is one of the simplest you will find but can be a pain. RustfreeMike is correct, The control on the left is an electro mechanical switch that incorporates a capillary tube for temperature control. The switch goes through two A/C relays mounted just under the dashpad behind the Tach. They turn the compressor on and off as well as control the fan speeds in conjunction with the fan switch on the panel. When you turn on the A/C the fans go on even if the panel fan switch is off. My car is wired so the fans will run with the A/C knob on, even if the ignition is off. Dead battery alert. I am not sure if this is normal. I have never been able nor do I want to try to figure it out.
When working behind the panel, be extra careful with the other controls. The rest of the system, the heating, is all vacuum controlled and the rotary control to the right of the radio and the fresh air vent lever above the radio are very delicate. It is very easy to break the plastic vacuum nipples off. They can be repaired if you are good with epoxy and it is almost impossible to find replacements. If you do they are very expensive. The vacuum hoses are a rats nest back there. Be careful pulling on them. If you can, replace them with new hoses. Most people, myself included bypass the thermal control that is attached to the heater box.
Good luck. I don’t envy you. It is my least favorite part of the car to work on.

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Thank you very much for the informative guidance. I’m rather mechanically limited :rofl: I’ve got the xj6 booked in for my local specialist in 3 weeks. He used to work on my 95 xjs, so I trust him. Never should’ve sold that xjs​:scream:
So far the series 1 is doing swimmingly well. I need a replacement right fuel pump and an odd vacuum noise from right side passenger foot well under load. But other than that really good.

The right side passenger foot well is were the vacuum lines for the heater controls pass through the firewall. There are, I think, 3 hoses that pas through a small round plate about 2/3 of the way down the firewall in the engine compartment.
Vacuum in. The larger of the hoses
Vacuum out to hot water valve
Vacuum out to fresh air duct control.
If you hear a sucking sound under acceleration then one or more of the hoses is cracked or broken. After nearly 50 years, if the hoses are original, it’s time for a change.

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Awesome Lawrence. Great guidance, thank you.
I’ll get on it. 50 year switch out :slight_smile:

This is where the vacuum line enter by the passenger footwell on the firewall. As you can see I was missing a line.
In the passenger footwell, If you pull the carpeting back you will see the other side. It is easier to remove the three screws and take the plate out and push new hoses through the holes. As you can see they are dimpled inwards so the hoses are hard to pull out. Cut them and feed through extra lengths that you will trim after reinstalling the plate. Once Inside the car, they go to the left and are held in place by a clamp on the side of the transmission tunnel before going behind the center console.
Good luck!


Thanks. I couldn’t figure it out, so this is super helpful.
Felling pretty good as a I replaced the right fuel pump yesterday & it works. yay :slight_smile:
Realized I overpaid for the pump from SNG.

Thank you @listarr4. Great advice. One of the 3 lines have been cut and taped off. The tape had come loose and air was escaping on acceleration. Cabin now super quiet.

Glad to have helped. A cut line means you have lost either all of your heating or the fresh air vent, depending on which line was cut. Here is the vacuum diagram form the Series 1 shop manual.