Hello All! Had a quick question about the AC and venting controls. The knobs for controlling the HVAC seem to work fine for me, but I'm having trouble understanding what each one does. The knob on the left has temperature settings in auto/manual mode, which my be on backwards for me? as the knob adjusts away from the settings. The knob on the right controls fan speed so far as I know.

But The bottom lever though seems to be a mystery! It doesn't do anything on my vehicle. I'm also not feeling any air out of the front facing vents, all air is coming out the defrost/window vents. I'm assuming I'll have to fix something, but is there a control for selecting which vents are active?

Currently away, but can add pictures to clarify my question later if its unclear.

 

The bottom lever changes the bias of cold to hot between the floor and face vents. It doesn't change the overall temperature, but you can have warmer toes and cooler face for example, by sliding the lever to the blue setting. On the red end the vents will have the same temperature.

The system is totally automatic, except when in the defrost setting. Then it goes to max heat and max fan speed and puts all the air to the windshield. In automatic mode, which is when you select a temperature, the system determines the fan speed ( up to the maximum you have selected) and it chooses the most appropriate vents to send the air. The centre vent will only open when cooling is called far, and it can take a few min for things to stabilize and the vent to open.

The usual setting for automatic is mid range on the temp scale (Usually about 21-22°) and fan on position 2.

 

Thank you that was extremely helpful. I appreciate the time to follow up. That will definitely help me to troubleshoot.

 

The defrost vent is vacuum actuator controlled. If it doesn't close, the center vent CANNOT open with its own vacuum actuator, as they are mechanically interconnected. The system, with no vacuum, closes the center vent and opens the defrost vent.
The two vacuum actuators are, in turn, controlled by solenoids. So your issues could be lack of vacuum, busted defrost and/or center vent actuators, or solenoids or solenoid control. The flaps that the vacuum actuators control also are known to sometimes stick.
Jon

 

You can download a copy of the Delanair MkIII HVAC system for your car at the following link, around post #20.
https://www.jaguarforums.com/forum/x...ispreloading=1

 

Thanks Jon! Exactly what I'm hoping to find out, thanks for narrowing the search down for me. I'll be doing some tinkering with it now that I better understand the settings. I'm assuming its a vacuum issue since the car sat for what appears to be an extended length of time.

 

You access the vacuum actuators by removing the lower dash panel below the glove box, and the front cheek panel on the side of the console that has the vent in it. It also helps access to remove the interior of the glove box. Vacuum comes from right side of the engine thru a small check valve. There is a vacuum reservoir also in the circuit.

Jon

 

Thanks to the provided details, I was able to get the settings sorted and found the side vents and lower vents were functional! I didn't give time to test the center vent as that was just a side project to what I was really working on (lower quarter windows, hydraulic pump not working)

 

Jon, where is the vacuum reservor located in a 1988 v12? Just can't find it?
Cheers
Alfredo

 

On a LHD car, its under the plate where the pedal assembly would mount on a RHD car. Assuming your car is too early for ABS, it would be the plate under the windshield washer fluid reservoir.

Jon

 

As always thank you for your help.

Alfredo

 

About that slider on the bottom…. The max variation it was intended to achieve was 3 deg. I assume that meant 3 deg C, or about 5.5 deg F. At full “blue” and the temp dial set to 75, would might expect something like 70 at your face. But when you set the heat to 75, it sure isn’t pumping out 75. It’s pumping out much warmer than 75 when it’s cold and much colder when it’s hot. This makes any difference top to bottom difficult to discern.

 

Thanks again for everyone helping on this. I've even got mildly cool air coming out of the vents! I'm assuming I'll need an AC recharge at the very least - The alternator wines a bit when starting with the AC set which I believe is the AC trying to activate without cooling. Any advice on that is welcome.

However, I'm more confused about the dial on my temperature selection. I was playing with it yesterday and I couldn't find a method to make the arrow point toward the numbers. So my question - was the selector reversed on RHD models, and my knob is from a RHD vehicle?

 

Jazz'n'Jags,

The controls are the same on LHD & RHD cars

Paul

 

Thanks. Guess I need to see if this has been broken in some way then