Pictures of the part are at the end of this post.

Anyway, I've grown weary of a non-functioning HVAC unit in my '87 XJ6. I finally had a local shop put a manual valve in the heater core hose this week, as the car will not heat up at all in the winter, and seems to have hot air coming through the system in the summer. The valve was installed above the car's own mechanisms, not in place of them. I did this mainly as a way to cut hot water off in the summer.

Before I threw in the towel, though, I made one last attempt tonight. The symptoms are the car seemed to blow the same temp air (i.e., as cold as it can go) on all settings, and the whole system is stuck blowing air out all the vents at once. No matter how you turned the dials or adjusted the temps, I could never here servos or motors working behind the dash.

First I decided to change all in-line fuses I could find. This amounted to four fuses. They all looked good, but I swapped them anyway.

Then I had a new A/C amplifier lying around that I had bought last year. I had installed it once before, to no effect. I installed it again, this time making sure to properly ground the unit.

Well, we made a little progress. Turning the temp dial seemed to cause things to whirr and click behind the dash. It was cold night outside (55 degrees) and I made sure to have the car fully warmed up before doing these tests, by the way. So, with the control knob set to "NORM," I put it on 65 degrees. The system gradually cut the fan speeds down until they went nearly off. And I think it finally stopped sending air to all the vents at once (but it's still sending to both dash and defrost vents at the same time).

As I moved the dial up to the 70-degree mark, the fans came back to life. The temperature didn't change, though -- full cold. Then I figured out what was happening: The car was trying to blend in hot air from the heater core, but couldn't. Whatever servo or valve opens the heater core valve to allow air to warm itself up wasn't doing it.

So I headed back home from my test drive, put the car in the garage and decided to flip through the modes again to see what it would do. And it promptly stuck itself in defrost mode, full code, locking out the controls.

I've had it.

Anyway, I found a couple of things for you guys to ponder:

1) Driver's side kick panel, there is what looks like a small vacuum canister mounted to the side of the HVAC box, high up, almost under where the ignition key goes. It's got a vacuum line going out the bottom of it, and a flat rod coming out of the top of it. I can't tell that it's actually connected to anything. I can move the rod back and forth at will.

2) Passenger's side kick panel revealed this plug, which wasn't plugged into anything. Pics below:


Should this be hooked up to something? And is it even an HVAC part?

Anyway, I'm kind of done with this. I'm not just going to run the A/C in the summer and cut off the hot water manually, and in the winter, not run the system at all and carry a space heater in the car and hope I don't burn it to the ground.

Jess

 

Disclosure---I'm on my first cup of coffee

Those non-used wires are not related to the HVAC system.

Vacuum actuator: sounds like the lower heating flap actuator, which would be related to air flow direction, not temperature regulation. It has vacuum at all times unless "DEF" is selected.

Cheers
DD

 

1) have you replaced the Heater Valve? sounds like it is stuck closed.

2) have you checked the Fan Resistor? could be burned out.

3) if you hear whirring and flaps moving open or closed, the Servo is doing its job.

4) if 1 and 2 are ok, then your TEMP Rheostat could be bad.

 

Unfortunately if any of that requires removing the dash and/or a lot of parts from the center console I'm pretty much stuck.

I'm most interested in what's involved with replacing the heater valve. What kind of job am I looking at there?

I think the thing that's most irritating about the servo/control/etc. is that you can get things to whir and move sometimes, and then sometimes you can't. It's intermittent.

Jess

 

-Remove the the two hoses from the heater valve. Sometimes this is easy; sometimes they're stuck.

-Remove vacuum hose from heater valve.

-Remove two small bolts/nuts holding valve to the firewall. 5/16th wrench size as I recall. For this you'll have to remove the air intake grille at the base of the windshield to reach the nuts. The grille is held in by friction pegs. Wriggle it upward evenly and carefully to avoid breaking them ...which sometimes happens no matter how careful you are. Jose has mentioned a clever trick of using string to pull the grille upward

-Assemble in reverse order

Cheers
DD

 

Doug,

That sounds doable for me. The one thing I can add to my diagnosis list is I drove it 6 hours round-trip today but didn't turn the system on; the transmission tunnel got a bit warm and I could feel what felt like warm air leaking out from various gaps, vents and panels around my legs. As soon as I'd turn the system on, though -- full cold she went.

In other words, it feels like warm water is getting into the heater core, but as soon as I activate the system, it no longer feels like the core is charged up with hot water, if that makes any sense.

If I can ever get it to where I can manually choose full hot or full cold (by either manually cutting off the hot water into the heater core, or by pulling the 15A fuse for the A/C compressor clutch), I will take that as a win.

Jess

 

Entirely plausible

The default mode is to have the valve open and hot coolant flowing through the core. But...if the system's brain thinks cooling is called for, it'll give orders to close the valve.

Wiring in a compressor cut-out switch is easy. This will prevent air from being refrigerated but won't ensure that the heater valve stays open.

A manual method to control vacuum to the heater valve is another matter....requiring more mulling



Cheers
DD

 

pulling the grille:

use fishing wire, or a guitar E string, wrapped between both hands, slide it under the sides of the grille, then pull up a little at a time on each side.

also a thin plastic strap does the job even better too. Just see-saw it under the grille until you hit a "stop", that's the Pin.

Prying the grille with a metal tool will always cause damage to the paint, so avoid using a putty knife or screwdriver, or anything metal.

the rest of the removal of the Heater Valve is like Doug said.

Doug, you can use two new, 1/4" to 3/8" self-drilling hex-head bolts, (thicker than the ones you are removing), and using a small ratchet, screw them at the firewall from the outside, then you'll never have to remove the grille ever again.

 

Jess,

There a couple of simple checks that can be done to verify the operation of the climate control system. For the climate control system to respond to the temperature inputs it requires a couple of parts. First is a working amplifier, second is a functioning feedback potentiometer, and lastly a functioning servo.
There are a number of items controlled by vacuum...hot water valve, dash facia vent, lower heat flaps, freshair flaps.

If you are willing to proceed with several diagnostic tests requiring a 9 volt battery, a multi meter, and removal of the left transmission vent cheek panel..im confident we can solve your AC issues. Just let me know if you want to proceed.

Cheers,

Gary

 

Jess,

There a couple of simple checks that can be done to verify the operation of the climate control system. For the climate control system to respond to the temperature inputs it requires a couple of parts. First is a working amplifier, second is a functioning feedback potentiometer, and lastly a functioning servo.
There are a number of items controlled by vacuum...hot water valve, dash facia vent, lower heat flaps, freshair flaps.

If you are willing to proceed with several diagnostic tests requiring a 9 volt battery, a multi meter, and removal of the left transmission vent cheek panel..im confident we can solve your AC issues. Just let me know if you want to proceed.

Cheers,

Gary

 

I've got all those things but I'm not an expert on multimeter settings. You'd have to get pretty exact in what the settings need to be before I can do that part. If you're ok with that, I'll go for it.

Jess

 

My .02, more like .01, in reality.


1. check out the vacuum diagram for this engine/car. Under the battery tray, on the fire wall are two small spigots. Hard, if at all to see, location more like by feel. Make sure that the vacuum lines are on the correct spigot. Jaguar did allow for this by making one ;larger tan the other. Theory, the system must have reliable engine vacuum to function.


2. As discussed, install a compressor "cut off" switch. Many other cars use the idea. I think that this semi-dodge will assure warm air if the system has no colds to try to introduce.


3. A PO replaced the vacuum operated water control on my car with a generic one. Plastic. Not mounted to the fire wall. It relies on the heater hoses for support as well as supply.


4. In my car's pre lump stage, AC was "variable". It is not activated yet. But, I think it's issue was a lack of dependable vacuum. Why, not determined.


5. I added a manual valve to the hose that did not connect to the vacuum switch. I call it my summer/winter valve. Closed. No hot water in the matrix. Power ventilation in modest temps feels good.
Open, nice warm air in the cabin. Temp contero and fan speed contro, function nicely.


6. On cold days, I select full defrost. Max air, max temp. Nice....


Carl