Almost every time I start it hot, it may take 3 - 30 min's. for the A/C vents into the cabin to open up. Sometimes, a pothole or a bump will seemingly cause it to open, bur not always. I thought it might be low freon, but the spy glass on the dryer says no.

Would someone who has actually fixed a few of these please post a how-to on troubleshooting and repairing the vacuum servos? Also, the vents on the L & R sides don't ever seem to open fully, barely any air comes out.

I've read Kirby Palm's BIBLE - Experience In a Book, and on page 544, he says the Delanair MKIII system is used from 1987-On.
Page 546 is a Vacuum Diagram for 87 - 93, and it shows a center vent flap actuator and a solenoid vacuum valve for the actuator. It goes into GREAT detail about the electric servos on the Delinair Mark II, but nothing about the Mark III. I am guessing there could be corrosion on the harness connectors to the ECU, but where is it? How do I get to it?

This is a common problem, I've heard. Do I need to purchase a factory manual, DVD? Please post any links to these, please.

 

The climate control module its item #1 in this illustration

Air Conditioning Components - Parts For XJS from (V)139052 to (V)179736 | Jaguar Heritage Parts UK

It resides behind the RH console cheek panel.

Also seek out and clean the small wiring connectors for the system. They are often corroded, causing erratic operation. Look for the tiny wires and tiny connectors. There are half dozen or so on either side of the main climate control casing....a couple of 'em up rather high and hard to reach. Clean the two main system grounds as well. You'll see them on the vertical dashboard braces.

A copy of the Delanair Mk III manual is bouncing around here somewhere. I'll try to find it. All the electrical checks are meaningless if the connections are not 100%, though....so you can't really skip that step

Cheers
DD

 

Go to post #19 of this thread.....

https://www.jaguarforums.com/forum/x...-manual-83961/

....and you'll find a link to a Delanair MkIII manual

Cheers
DD

 

So, after cleaning all the connections and connectors, I would proceed to test the circuit as follows: From page 7 of that pdf, it says pin 18 of the ECU outputs voltage to the center vent solenoid. If it's there, the solenoid allows vacuum to the actuator. If not the ECU or it's sensors should be checked. Other things to check are the restrictor valve and the vacuum lines, right? I'll post again with photos after I fix it.