’91 XJ-S coupe, 5.3L V12, 100,900 miles.

Had my AC repaired earlier this summer, and its…almost there. Replaced the compressor and belt, and now it does get fairly cold. However, the cabin never really feels cool, just somewhat dehumidified. On really hot days, leaving the windows open and driving fast works better.

I tested a few things and eliminated the following as issues: cabin temp sensors are fine; fans and fan speed control are fine; temperature control is fine; fuses are fine.

Was going to adjust the AC amplifier but then I noticed that I don’t get a lot of airflow from the center vents. On cooler settings, air blows through the windshield defrost vents as strongly or stronger than the center vents. Seems to fluctuate in strength as well. However, on warmer settings (i.e, from halfway down the temp control) there is no airflow from the defrost vents or center vents, just the floor vents. On Defrost, warm air flows only from the defrost vents as it should.

So…seems like the airflow flap does work, but only for directing higher temperatures to the floor or defrost vents. Is there a way to adjust the flap so it fully closes off the defrost venst allowing cold air to flow to the center vents only?

Should also probably mention that I found tiny bits of gray foam on the dashboard and console when I first got the car back from AC repair, and a few more bits blew into the cabin the first few times I used the AC. Damaged or rotted vent foam? Any way to repair?
Thanks.

 

Getting the AC is a major job.

I would first check the servo motors are working. Being a 91 I beleive it wil be the MK111. If you remove the blower fuses and turn the ignition on (do not start the car) then yo can move the rotary controlls and hear if the motors are running.

My bet would be corroded terminals in the connectors around the AC unit in the dash. Also check out the vacuum switches there are 2 on each side these rust from windscreen leaks and then fail.

 

I had a similar issue with mine and was able to repair with help from DD and SARC. It's not rocket science to fix, and just requires a couple cheap tools to troubleshoot. It is a minor pain though as you're working inside the dash and center footwell. The system on your '91 should be the same as my '88 MkIII Delanair.

Sounds to me as if your defrost vent is not closing properly. This is controlled by a vacuum actuator that is inside of the dash, located above and to the left of the glovebox. There is an interlock that prevents the center vent from actuating until after the defrost is closed. The vacuum actuator works by means of a vacuum sent from a solenoid valve located in the RH side footwell. No vacuum to the defrost vacuum actuator puts it in the 'open' mode. This is the failsafe so your defrost will always stay open on a cold winter's day. The signal to the solenoid valve comes from the climate control ECU, which is located inside the dash just to the left of the glovebox.

If I am correct and your defrost actuator is not working, one of three things is happening:

1. Electrical signal isn't getting to the solenoid actuator, through either corrosion on the terminals or faulty climate control ECU. ECUs can be a bit pricey I think.

2. The solenoid actuator is faulty and is not responding to the signal from the ECU. The solenoid actuators are somewhat common failure items usually sold in pairs, and can be had for $60-$100 from the usual sources. This was the problem in my case. I gambled this was the problem and bought a spare on sale ahead of time, as I didn't want my car out of commission for an extended period if this was the case.

3. The defrost vacuum actuator is seized and requires replacement or refurbishment.

I would rule out a fourth possible case, that your climate control vacuum reservoir isn't holding a vacuum, because it sounds like the other vacuum solenoids (or at least the recirc and coolant solenoids) are working properly. It still may be worth investigating the check valve located in the rear RH of the engine bay just in front of the firewall, as in my case this had also failed and wasn't providing a very strong vacuum to the reservoir when the engine RPMs were low.

It is possible your center vent actuator is only partially opening or nonfunctional instead... we'll investigate that as well.

To properly troubleshoot, you're going to need to remove the passenger side footwell covering and glovebox. Hopefully you have small hands, as you're working in tight spaces. Print out a copy of the climate control routing diagram from 'the Book' for the Delanair MkIII through '93. You're also going to need a voltmeter and vacuum gauge/pump such as this one:
Brake Bleeder and Vacuum Pump Kit

The solenoid actuator looks like this:


The website in the next link will cover removal of the glovebox and getting access to the see the vacuum actuators. Ignore everything regarding the heater core and coolant system, you don't need to mess with that. You can also leave the center vent trim in place. Get to the step where you unscrew the ECU (don't disconnect it from it's harness!) and then stop:

GoFlyRC.com - 1989 Jaguar XJS Coupe

Identify when the vent actuators are, as you're going to check their operation. Next the RH side footwell covering needs to come off. It's held in place only by the two screws on the heater vent. Look around inside for the solenoid actuators, which are mounted on a plate as a pair. Be gentle when messing with the vacuum lines, as they can pull free from the far end and are tricky to reconnect there. Find the solenoid actuator with the green line leading off of it, this controls the defrost vent. Start the car (needs to be running to send vacuum to the climate control) and set the climate control to defrost.

While observing the operation of the center vent actuator, set the climate control on 65F and move the fan switch from defrost to high. When everything is working properly the defrost vent should close followed shortly by the center vent opening fully. If your center vent only partially opens, you can try fixing its operation as described in the final portion of the above link. If the defrost vent never closes, continue on with the troubleshooting below. (There is a third option that the defrost closes but the center vent never opens... if that's the case follow the troubleshooting below focusing on the center vent solenoid with the black vacuum line instead of the defrost solenoid.)

With the car still running measure the incoming vacuum from the white vacuum line using the vacuum pump gauge, should be about 10"-15" if my memory is correct, if no vacuum the vacuum line is disconnected upstream of the solenoid actuator.

Assuming you're getting vacuum, reconnect the white vacuum line and apply about 10" vacuum to the green vacuum line using the vacuum pump. The defrost vent should close followed shortly by the center vent opening fully. If the defrost vent does not close with vacuum applied, problem identified: defrost vent actuator. You'll need to dig around inside the dash to get it out and repair/replace.

If the defrost vent does close with vacuum manually applied and the center vent opens, the problem is either with the ECU or the solenoid actuator.

Shut the car off, pull out the defrost solenoid actuator, and apply voltage across the solenoid's electrical terminals with a common household 9V battery. You should hear a small click, and be able to suck air through the vacuum lines. If not, problem identified: the solenoid actuator is bad. Purchase and install replacement, then check operation of the system.

If the actuator works correctly most likely the problem is with the climate control ECU. Again with the car running, climate control set to 65F and fans on high, measure the voltage across the leads to the defrost solenoid. DON'T SHORT THE TERMINALS OR YOU'LL FRY THE ECU. If it doesn't read 12V or something close, you've confirmed the problem to the ECU (or the wiring). If it does read 12V, terminals on the solenoid are probably corroded and need cleaning.

If you decide to remove the center vent trim at some point, you may as well upgrade your center vent to the later style used in '93 onwards. Instead of having the nonadjustable center section that blows air straight to the back, the left and right adjustable vents span the enter surface. Makes a huge difference in being able to redirect air. You can get the part from salvage yards for about $75. Worthy upgrade in my opinion.

Cheers,

- Will

 

Excellent writeup Will

 

Nice one Will & thanks for sharing

 

Can't thank you guys enough for taking the time and trouble to lay this out in such detail for me. Plan to tackle it this weekend and will report back. If you ever get to NY look me up so I can thank you in person!


Think the very first thing I will do is thoroughly clean all of the associated contacts and grounds, that solved a host of other issues when I first got the car.

Ian

 

@Will

That is THE definitive thread on those pesky solenoids !

@Jim

Could we make this a sticky ? or a link in the FAQ ?? This question comes up a lot. Another one that we answered (correctly) a few days ago was the "electric window not working because the switch is flaky", ie https://www.jaguarforums.com/forum/x...working-79747/ I think this is worth a sticky too

 

Had a little free time today, so decided to try warrjon's test since it seemed quick and non-invasive.

Pulled the 25A blower fuses (one each side fuse box) and turned the ignition on. Starting with the Temp control at 65 and the Fan Speed on Off, heard a click each time I switched between Off and Low. Heard motor whirring sounds each time I clicked between High and Defrost

Leaving the Fan Speed control on any speed, the motors sounded again when I adjusted the Temp control from one extreme to another. When left on the highest temp, clicking between Off and Low now produced the motor whirring sound.

So it appears that the servos are working.

Does this imply that the ECU is functioning properly, and that signals are being sent and received correctly? What would be my next logical step, check vacuum and the mechanical flap travel?

Thanks again,

Ian

 

Have you verified that the A/C is actually working 100%? Connect gauges and check pressures. Also check the temp of the evaporator when the A/C is on. Working on the controls is pointless if the A/C is not cold enough. I know you just had it repaired. That would be my first suspicion. Most times you will find that shops overcharge the system. This will caused increased pressures and lack of cooling performance. Once you have determined the evaporator is actually running cold then look at the controls.

 

Doesn't necessarily imply the ECU is good. It can fail in such a manner than only certain controls are impacted.

However, the solenoids seem to be the most common failure...

In any case without observing the operation of the actuators as described above you're not going to know where the problem is. You don't necessarily have to remove the glovebox and could do some of the troubleshooting by just pulling the passenger footwell cover. But without doing that you won't see the operation of the vacuum actuators and be able to observe full travel, and it only takes about 10 minutes to pull the glovebox.

Cheers,

- Will

 

The initial problem states that air blows "as strongly or stronger" through the defrost than the center vents. When the actuators are working properly on any setting other than defrost there should be barely any perceptible air from the windshield defrost vents, even accounting for foam decaying away. The center vents should be kicking out quite a bit of air on 'high.' Of course one fan or the other may not be operating correctly, which will reduce the air coming out the center vents, but that wouldn't explain for air coming out the windshield defrost.

Cheers,

- Will

 

The shop I deal with is a longtime local Jag specialist, he worked on my XJ8 before the XJ-S. I purchased the car from its original owner, who was his longtime client as well. So I'm confident he knows his way around Jags in general and this XJ-S in particular. If I can't figure out what wrong here I'll bring it back to him as he always stands behind his work.

I don't think the air coming out is as cold as it could be, but with reduced airflow its hard to say if its sufficient or not.

I plan to pick up a vacuum gauge/pump over the weekend and continue troubleshooting.

 

Had to make a coffee run for the Mrs. so took the opportunity to do a little more testing. Popped off the center vent wood trim (a small putty knife worked well), pulled the center vent out, and felt around inside to see just what was happening with the top (demist?) flap. The answer: ain't nothing happening.

Regardless of what temp or fan setting, the flap stays in a down position. When I manually push and hold the flap up, airflow stops coming out of the defrost vent and blows much stronger through the center vent opening. I could see the vacuum line connected to the actuator but apparently I either have no vacuum to it or its not responding.

Am I on the right track here?

Thanks,

Ian

 

Most definitely!

 

Add another item to the list: turns out the LH (driver side) blower is not blowing.

Swapped fuses, no difference. Both fuses work with the RH (passenger side blower). Both fuse panels sockets measure correct voltage.

Gonna pull the appropriate cover panels and see if cleaning the contacts and grounds helps. Will also check ECU voltages.

Worst case, I'll pull the instrument panel and go in after the LH blower and see if the board needs repair. I removed the panel once already to replace dash instrument lights (four of the five 194 bulbs were dead) but the lower right side of the tach still isn't well illuminated. I may just do an LED upgrade while I'm in there again.

I am determined to get this all sorted before the leaves are off the trees!

Ian

 

That's a bummer, but at least you are closing in on the issues!

There is lots of information on fan failures in the forum archives and 'the Book' as well. Sounds like you're well on your way!

Cheers,

- Will

 

Will, do you have any idea where new solenoid actuators might be obtained?

 

Try eBay, I think there are a couple of them up there now.

 

Most Jag parts suppliers stock them. They fail after about 20 years or so and seem to be a relatively common item.

I'll see if I can find you a part number. Googling "XJS Climate Control Solenoids" turns up several instant results though.

Cheers,

- Will

 

Yep, thanx Will. bought the pair as spares :-)