XJS Delanair Mk3 Repair

First off I needed to replace the leaking heater core and replace the connectors that had been damaged by coolant.

 New Main cabin power connector got this from Jaycar

 All of the junk in the AC box, This needed cleaning.  These pics is upside down but it gives an idea how bad it was in there.

Dead Heater core, definitely been leaking.

  So I cut the front off the AC box to gain access to clean it.

I forgot to take a photo but I sealed the front of the box up with a plate of 1mm aluminum, riveted and silicone.


I had my AC re-gassed last week and not everything was well. I had cold air coming from the defrost vents, Hot air from the footwell vents and no center vent operation at all. My car is an 1989 with the Delanair Mk111 system, this system was used from about 1987 until about 1992.

A big thanks to the folks on Jaguar Forums particularly Doug for the Manual, which made diagnosis easier and quicker.

Anyway I am going to try and simplify diagnosing problems with this system. As it turns out I had 3 different issues, that took me the best part of the day to find and rectify. At least 2 were caused by having the dash out of the car and replacing the heater core

Hot air in the footwell was caused by the lower blend flap being re-installed incorrectly. A PITA to fix with the dash back in the car.

To reposition the lower blend flap I had to remove the lower blend flap motor then reposition the flap in the correct orientation and re-install the motor. Re-positioning the flap I needed to get my fingers up inside the AC unit and turn the flap.

Remove this motor

Fingers up here to re-position the flap.

With this fixed I could now vary the air hot or cold in the footwell. My next problem to solve was no air from the center vent which is controlled from a vacuum solenoid in the RH footwell. The left solenoid (the rusty one) when turned on by the AC controller opens the center vent. I hooked a battery to this solenoid and it operated correctly with a current draw of under 500mA so I made the assumption this solenoid was good.

Use 2 of these jumper wires to probe the ECM, this will prevent inadvertanty shorting any of the pins, and that would most likely damage the ECM. These jumpers can be found in old PC's

Following the diagnostic process in the Delanair manual, I traced the fault to the AC controller. The controller drives these solenoids directly. So next was to remove the AC controller and find the faulty component. This PCB is a multilayer and all the tracks run on the inner layers as well as being conformal coated. It was a real PITA to trace everything. So I just measured all of the components starting with the transistors, voila the 2nd one was toast. Replaced this and after putting it back together I had air from my center vents.

This repair worked for a couple of months before the centre vent decided it wasn't going to open any more. I ended up jerry rigging a solution to get the vent open until I could pull it apart and repair it properly.

The problem ended up being damaged traces in the PCB and as all the races run in the middle of the PCB is was impossible to find where they went. So I ended up buying another ECM off eBay and luckily for me it was a good one. This was caused by the connector  spade terminal plastic insulation being broken and the + shorting on the back of the radio, this took out the transistor and damaged the traces that worked for a while before fusing.

This pic shows which transistor was replaced.

Here is how I repaired the traces. You can see the 2 links I added to the PCB. After putting it all back together I now have operational centre vents. Next is to pull the drivers side blower and fix the it.