Hi guys,

The A/C on my '84 XJ6 works intermittently...the freon level is fine, but the A/C will kick in and out regardless of settings, blowinf very hot, or OK cold. Any ideas?

 

The "could be" list is long.

One of the easier items to check is the heater valve. It's on the firewall.

Set mode dial to Auto and set the temp dial for max cooling. Let the system stabilize for a minute and then take the vaccum hose off the heater valve.

The heater valve should open. You can watch the little lever arm operate.

Put your finger over the end of the vacuum hose. You should feel vacuum. If not make sure the hose is in good condition. If the hose in in good shape but you don;t feel vacuum, you have a control problem

Reattach the hose. Have a helper slowly operate the temp dial from cold to hot a couple times, slowly, while you observe the operation of the heater valve. Is it operating smoothly and consistantly? Is it sticking?

(The heater valve should be fully closed when max cooling is called for. For heat, or anything less than max cooling, it should be open)

Next, a question.....

When the climate control does something you're not expecting, do you hear a faint whirring in the dash? You'll have to listen carefully.

If you hear a faint whirring, that's the servo motor operating....and it operates only when ordered to do so by the climate control amplifier. it's common for the amplifier to give weird commands to the servo. In most cases the amplifier itself is the culprit. About $300.

If the weird operation is NOT accompanied by the whirring of the servo then you have a problem downstream of the servo....that is, not directly related to the control side of the system.

Prepare yourself for the possibilty of replacing the amplifier. Unfortunately there is no bench test to verify that it is faulty before taking the plunge.

This barely scratches the surface of climate control trouble shooting but it's a start!

Cheers
DD

 

...I checked the servo and vacuum and alls well. I do hear the servos opening the vents, but what happens typically is that it will just blow hot air, then maybe..suddenly..it will blow cold..then hot again. When it's hot, the servos will close and then it will blow cold.

 

To clarify, I was referring to the servo motor, not the vacuum operated servos that control some of the flaps.

If you hear the *electric servo motor* whir when the crazy things happen, you probbaly have a problem on the control side of the system. That is, something is commanding the servo to do crazy things. And the servo is what controls the vacuum switches, fan speeds, flap linkages, etc.

If the crazy things happen without the servo motor whirring away, then you likely have a problem downstream of the servo motor and unrelated to the control side of the system.

My gut feeling is that you need an amplifier. It's the most common culprit when craziness occurs. Wish I could be certain, but I can't.

Cheers
DD

 

https://www.jaguarforums.com/forum/p...-manual-95169/

I have one for sale on this Forum! It allowed me to fix my system...

 

How difficult is the amp to change out? My 87 xj6 does the same thing. It can be working fine and then it reverts to a welding setting without notice. Is this the same amp in the xjs? I have several of them around. I race an xjs and the climate system is always stripped out of them to save weight. Thanks, Kev

 

I'm also curious where the amplifier is located. My '81 XJ6 just started acting up today, I got on here to ask about it and my question looks like it's already been answered. I've got a '83 parts car that may or may not have a good one in it, won't know until I plug it in.

 

 

Actually, the amplifier is pretty easy to get to, that diagram looks more confusing than it is.

If you remove the screws that hold the side panel of the console...where the little vent is that direct air to the foot well...and carefully slide the piece off it's clips, the amplifier is about mid way up/down. You have to reach a bit to get the wires, but it's a pretty straightforward operation.

 

Thanks, first chance I get I'll swap mine out with the "might be ok" one from the parts car and see if it fixes it-or just changes the problem.

 

Actually, you don't really have to remove the old amplifier, to install a new one.
All you need to do is disconnect the wiring harness (round/white) to the old amp, and plug the new one in. It will tuck neatly to the side of the kick panel, under the lip of the console. Just be sure to plug in the fuse / ground wire too.

The old ones can be a bugger to get out, and there is really no need for it to be in those tight confines, anyhow.... All the cradle for the old one does is give it a place to rest. It has no bearing on the operation.

Cheers
David
Everyday XJ