Heater control is OUT of control!

Robert,
it is called the Auxiliary Fan Mod. Jag Graveyard did not invent it, they simply packaged the needed parts and sell the kit for $10.00. I bought the kit from them too, ignorant that the instructions were posted for free at jag-lovers and the parts cost less than $2.00 at Radio Shack. The idea is to apply the same aux. fan circuit that came in the XJ-12 to the XJ-6.
There are annoying after-effects to this Mod: The auxiliary fan makes a whinning noise whenever it runs, so making it come ON everytime the Ventilation switch is turned ON can be annoying. But it does help to keep the coolant temperature under control in hot summer months. The second after-effect is that in Winter months in cold climates, you would want the opposite, that is, no auxiliary fan, because you need the heat, so having the aux. fan coming on in 20 degree temperatures is absurd. I end up disconnecting it in September every year so I don't get caught by surprise on a cold morning. Again, an annoyance. Maybe an ON-OFF switch would complete this mod. but drilling holes and adding switches? Where? nahhh.
The instructions and Parts needed are also posted at the Motorcars Ltd.
XJ Forum, free.

Finally, I think I have something to contribute.
There is a company called Jag Graveyard, they are on the Net.
they sell a diode for your aux. fan.
What this does is turn on your aux fan whenever you turn your a/c on , no waiting!CHEAP FIX
Works great on my 87 XJ6!

great! I got that tip from Phil Prince at Motorcars Ltd. so credit goes to him.

Yes, a dollar part can create chaos. The Series 3 XJ-6 runs hot, in summer especially, but my 1965 S type is a pleasure to drive without A/C and I can't figure that one out. Plenty of air comes in through the side window vents and the vent by the wipers. Old cars are so simple without so many
gizmos to troubleshoot. And yet, the S type is so similar to the XJ.

Another tip: To lower the engine temps in my XJ-6, I sent all the exhaust pipes to Jet Hot Coatings (they're in the web), where they coat them with a ceramic and silver mixture that actually lowers the temperature. They end up looking a bit like polished chrome, but not as shiny. Hot rodders do it to the exhaust parts in their fabulous cars. I have noticed a cooler running engine and exhaust so the coating must be doing its work, especially under the driver's floor where it gets so hot in summer. You might try that for a cooler interior. Since I'm on my 14th year of owning my 1984 XJ, spending all my money on it is not a problem, so I'll take the petty cash!

JAM.....take a gold star out of petty cash!

I took out the check valve...washed as you suggested...put it back in and WAMMO.....I got AC!

Thanks very much.

I hate to think of how hot I got driving her last summer because of a faulty $1.00 part!!! MORON!

Dennis
86\' XJ6

doing ok Dennis!.

The Amplifier is located in the left side (driver's) kind of sort of behind the stereo in that mass of wires and components, it has a big plug with about 20 wires going to it; you'll need a good light that won't burn the upholstery if it makes contact. Remove the left "scuttle" panel and plastic vent and the underdash panel for access.

The Servo is on the opposite passenger side, behind the scuttle panel, covered by a black plastic cover, assuming it was put back on if it ever was serviced. It looks like a miniature transmission with micro switches and vacuum hoses.

The Coil Thermostat is to the back side, above the Servo and the Stereo,
you'll need a good light. You'll see the silvery tubes entering the coil on its side. Look UP and BACK.

To test the check valve: run the engine for 3 minutes or so in PARK, turn the A/C to ON; with the bonnett (hood) open, remove the hose coming from the engine from the bottom of the check valve; The end of the hose should stick to the point of your finger if Vacuum is good, you should feel it "sucking" to your finger. If that's ok, then reinstall it and pull the other hose from the top of the valve and see if the valve itself stays on your finger with "sucking" action. That would mean the valve is good. If not, get a new one. (Dealer part I think). Substitution is usually the best medicine. There must be a generic check valve available at PepBoys, Carquest, Autozone, Advance Auto Parts, O'Reilley's, or Roy Rogers', the $ .99 variety.

Try washing the check valve in hot water from the faucet and a little detergent, making sure the ball inside moves freely. If no vacuum, you have a massive vacuum leak as Phil Prince would say, retrace all your steps.

A/C Amplifiers: there are a number of aftermarket substitutes developed by
different people: John's Cars in Houston has a substitute but I have never tried it. I'm told it's a good alternative to the $275.00 original part. Also, I hear the original part has a GM Delco sensor circuit inside, so
regardless, don't throw the old one away. Even if bad they're repairable.

Testing the Servo means watching the gears of the transmission and the micro switches go through their motions with the engine on and the A/C or Heater ON, it's an incredible show to see the Servo at work, it opens or closes all the flaps. It is possible to remove it and reconnect it near where it lives to watch it working. You will need a Service Manual to read on all the diagnostic steps. Get a CD Service & Parts Manual for under $25. at the Jag Dealer. Then you can print whatever you need.

Hope this helps you get started. I'm sure others know other testing tips.

I "checked" the check valve. Seems to work just fine. And there seems to be good vacume at the engine side of the valve.

Dennis
86\' XJ6

Hey JAM.....how ya doing?

Thanks for the check list. Where do I find the box pictured above? And how do I check to see if it is bad? Oh BTW the plastic check valve (the only thing on the list that I know WHERE it is) How do I check it?

Dennis
86\' XJ6

Hey JAM.....how ya doing?

Thanks for the check list. Where do I find the box pictured above? And how do I check to see if it is bad? Oh BTW the plastic check valve (the only thing on the list that I know WHERE it is) How do I check it?

Dennis
86\' XJ6

sorry, I meant the image below! too much octane in my eggnog. The A/C Amplifier, the Servo, the Coil Thermostat, a vacuum hose, the plastic check valve next to the battery, anyone of those could cause the symptom.