XJ6 & XJ12 Series I, II & III 1968-1992

only defrost

Old 05-25-2016, 08:17 PM
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Default only defrost

ok, the ac/heater only blows on defrost--nothing on high low or auto and temperature has no effect on whether the fan works or not.

I checked the four fuses, and they look ok, but I am getting replacements for the old ones to swap them out.

any thoughts. I couldn't figure it out from the existing threads, but I could be an idiot.

Old 05-25-2016, 10:07 PM
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My gut feeling is that your amplifier has died.

Do you have the factory service manual? It has a pretty good section on climate control faults.

When you select 'auto' and move the temp control dial, do you hear anything at all? You should hear a slight whirring sound. If you do, the system is at least 'trying' to work

On one of the heater core pipes, roughly above the handbrake shaft under the dash, is a small temp switch with two wires. Unplug the wires and jump them together. Any change?

Old 05-27-2016, 06:55 AM
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was the a/c working fine? The Servo is in charge of opening and closing the different Vents through a system of Rods and Levers. It also uses Vacuum to do it. There is a plastic Check Valve located by the side of the battery, connected to a Vacuum Hose. That hose goes thru the firewall and connects to a 'T' which connects to the Servo with other hoses. Find the Check Valve, remove it, and blow thru it from both sides. If one side lets air go through it, but not thru the other side, it can be assumed the value is fine. But if no air blows thru either side, or if air blows thru either side, the ball inside the valve is stuck. Replace it or try to unstick it by placing the valve in hot water for a while and blowing thru it to remove any grime.
Old 05-27-2016, 09:19 AM
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I was messing around in my shop yesterday. Fuses, the glass ones,
were a part of the fiddling. Several loose in my "electrics" box.
Good or bad? Test options, VOM or test lamp. As there is a battery on the bench, don't ask, I elected to use it. Easy, no interpretations.
Light on, it is good. No light, toss it. Only one of about twenty of various values failed. LUCAS!!!

Loose bubs of various shapes. Some in sockets, some not. Break
out the jumper wire. About 18" with alligator clips on each end.
Some two filament. All passed.

I've saved a cooling fan from a defunct computer. I noted, it is marked for 12v !!! Great. Tested it. Nice little breeze!! Some day, mebbe, it will become a powered vent for the boot. Minor petrol odor there, but no evidence of liquid leaks.

Old 06-05-2016, 06:25 PM
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Aha, I've had this exact problem, you probably read my post, there's a little "tab", if you will, that's behind the fuse box, it bridges fuses #5 and #6 (if memory serves) by joining the inner clasps of said fuses, power to only the outer side of the clasp means fuse #6 (I think) doesn't get power... And nothing except the defrost function works. Well, that was my problem, slight corrosion is all it takes.
The following 2 users liked this post by NathanDD6:
Jose (06-06-2016), UKcat (11-30-2016)
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