Anyone have a wiring diagram? I hear the blower motor relays clicking but they don't turn on. They were fine and now they arent!

 

here you go

 

Thanks you! Exactly what I needed and have now fixed my fans. I went all winter without heat in this car.

 

that quickly? haha! so what was the problema?

 

As simple as the fuse. I had replaced it before, the fans worked, and then they didnt. I swear I had checked it and got voltage both sides, which is why I didnt look at it again. Winter came and I didnt fancy kneeling in a foot of snow to continue diagnostics.

With the wiring diagram, I was able to see the control signals where there but couldnt see power into the relay. I figured broken wire between the fuse and relay. I start to test at the fuse and low and behold, no voltage on one side. Replaced and working fans. I have no idea what the voltage was the first time around which lead me down a blind ally and 3 months of frustration.

Of course, back then, the servo and flap control worked and now doesnt. So full heat, in defrost, all the time. I'll take it for now.

 

yikes! defrost is default for "something is wrong in the system".

I would look at vacuum, if the blowers are fine, and if the TEMP works...

There is a black & white check valve hanging near the battery in a "T" vacuum hose connection, and usually those check valves "freeze" with age, observe the orientation before removing it, (white half goes up), put it in a pan of warm water to clean it and see if it solves the problem.

(being a 12 cylinder I'm not familiar with the vacuum routing).

 

No, temp control doesn't work anymore. It did 3 months ago. I get the various fan speeds which are different on Lo, Auto, Hi and Defrost.

 

in HEAT mode, (TEMP at 85), you only get 3 speeds maximum from the blowers,

in A/C mode, you get the 4 speeds.

To get HEATED air, the engine and coolant must reach normal operating temperature before the Heater will work.

is the Heater Calve opening and closing? is it getting vacuum?
is the Servo getting power and vacuum?

I would remove the radio panel, then the radio, and check all the spade connectors behind the TEMP and MODE switches are in place.

also check the Fuses again, removing each fuse and replacing it.

 

Ukcat

Greetings...full disclosure..I'm the owner of Jag-Aire, LLC. Before you start removing components and tearing into the console..I strongly recommend doing some basic tests. All capable of being performed from the drivers footwell after removing the cheek panel with a simple multimeter and 9 volt battery. I have been seeing a large number of feedback potentiometer failures. These are a wire wound pots which are failing after 30-40 years of abrasion. Unfortunately, there is no direct replacement available at this time if it has failed and you would need to find a used servo. I am attempting to manufacture a replacement..but that is still some time away. Lastly, I am traveling today so I don't have the documents in front of me but you can download the manual for my amplifier from my website ..the sensing system testing instructions are included within. But basically, the amp has no knowledge what position the servo is in with out feedback. If the feedback pot is damaged..the amp will usually default to full heat or full cold.

Best of luck

Gary

 

I try to avoid assuming a repair will be complicated but I sometimes fall into that trap. As further reminder, to myself and others, of what folly that can be, here's a good example of how assuming a repair will be simple and always beginning with the basics is the right path.

Just yesterday I was working on my Mk II climate control. Two problems: the fans operated erratically and the center dash outlet didn't open in full cooling mode.

In looking at the wires on the fan relay I immediately noticed that 3 of the white connector covers looked melted. Now there's an easy clue if there ever was one. Sure enough, the associated posts on the relay had green corrosion. Corrosion = poor contact = high resistance = heat = melted covers. I cleaned the posts and connectors, a squeezed the connectors a bit for a tighter fit and, voilá, fans operating perfectly and consistently.

The mystery is why only 3 terminals showed this corrosion. The others were fine, and a quick look around revealed none of the usual signs of moisture (and certainly not water) behind the dash. Oh well, I'm satisfied for the moment. We'll see what the future brings.

Next, the center vent. I removed the dash outlet (it simply pulls straight off) and pushed the flap open with my fingers, proving that it isn't physically stuck. That was a relief. Next, I pulled the RH cheek panel and located the black vacuum hose that runs from the servo to the vacuum actuator for the center outlet. I attached a small length of vacuum hose and using a very high-tech bit of equipment...my lungs...sucked on the hose. Nothing. I could blow and suck thru the hose as though is was a drinking straw. It obviously was broken or disconnected....but where?

Since the dash pad comes off in 5 minutes the easiest place to begin looking was all the way at the other end, at the vacuum actuator itself. Sure enough....the plastic vacuum hose joiner was broken. Took 5 minutes to replace, 4 minutes and 30 seconds being spent scrounging through my collection of vacuum hose bits to find the right size joiner!

To test I first set the system to 'Auto" and "65". Then I pushed in the cigarette lighter. When it popped out I held the hot element 1.5" away from the inlet of the cabin temp sensor to trick the system into thinking it was August in Las Vegas. Sure enough, the system went into full cooling mode and the center flap popped open.

All in, about an hour spent.

Cheers
DD

 

I don't seem to have the check valve. The only thing I seem to have is a metal fitting on the end of a hose coming from the intake which reduces in bore. The reduced bore hose then goes in to the cabin where the heater valve hose comes out of. I wonder if this is a restrictor or one way valve. I'll have to check vacuum from the controls end of the hoses.

Oh and the blower fuse blew again. Then I noticed my voltmeter pegged at 18V. Great. Yet another (intermittent) problem!

 

ok, the good news, the circuit is being protected.

the bad news: the blower motors may be covered in grime causing overheating, which means removing each front seat, then each blower case, then a complete cleanup of the components, including repairing broken plastic pins for the blower case flaps, replacing foam seals at the flaps, and the worst part, the re-assembly.

I recommend you follow each step in the Factory Service Manual, there are no shortcuts.

the job is a satisfying learning experience. Makes you an expert at the stuff.

Could the Voltage Stabilizer be kaput?

 

I think the fuse blew because there was 18+ volts at the time. The current must have been above the 35A rating and it popped. The fans seem quiet, work well and blow a lot of air so I don't think they need an overhaul.

RE: voltage stabilizer - yes it could be. Are these removable or integrated? I'm about to go and play around with it.

I remember back in the day something similar happening to a '77 Datsun my dad had, it turned out to be a faulty ground strap. I remember him using a wire coat hanger from the engine to the body so we could get home. Apparently it can also happen with lose battery connections.

 

as an example, my old S type has a separate voltage stabilizer located inside the car near the fuse boxes, looks like a relay through which all power runs thru before it gets to the fuses; I think this method was carried over to the 420 and to the first XJ Series, but I am not sure of the Series 2, and certainly not of the 12 cylinder.

Could be that in your car it is built into the alternator. Attached is the electrical Manual, but I believe that one is for the Series 3 XJ.

you can also download the S57 Wiring guide here in the HOW TO QUICK LINKS

 

Fixed the climate control! Loose wire on the back of the temp control switch and a hole in a vacuum line.

 

I'm definitely stopping giving you advice! haha! you're a step ahead!

 

Good sleuthing !


Cheers
DD

 

Ha! Advice, and the back and forth is always welcome.

Thank you. Stupid little things really that I swear I went through months ago. The vac hose though, I'm pretty sure that's new because I think I moved it when putting in a new battery and it looped too close to the exhaust manifold.

 

Well,... My fuel issues are quiet for the time being. Now, on to the AC. Been in the mid 90's, so not an option.
Compressor not kicking in. Found the original thermal fuse disconnected and a replacement tied wired close by. Removed both thermal fuses and got no continuity from center contact to outer terminals. I assume blown.
Briefly jumpered around the thermal fuse and the clutch pulled in and all looked good.
The question,... What could cause this fuse to blow? Apparently the previous owner replaced it and the new one blew. Don't want to duplicate efforts.
Any ideas?

Thanks, Jim

 

I think they blow during an overpressure event, though the compressor has another overpressure safety switch in the back side.

the tied wire:

if that wire has a diode soldered in line with the wire, it most likely is the "AUXILIARY FAN MOD" which started in the early 1990's;

The idea is to connect the wire with the one-way diode, to one of the Red Relay wires and that causes the auxiliary fan to run continuously when the climate system is turned on, a/c or heat, so to help keep the radiator temp down in Summer. But you need to disconnect it in Winter for obvious reasons. It is also a very noisy modification, since the auxiliary fan is running all the time. The XJ-12 cylinder came like that from the factory, so someone adapted it to the XJ-6.