Some while ago I had a problem with lack of function of blowers for the climate control. I was getting no power from the microswitches to the relay. I pulled Climate Control Switch out and cleaned the microswitch contacts and it started up again. Recently, it konked out, came back and then konked out again. Figuring I had old bad microswitches, I replaced all the microswitches but this time it hasn’t solved the problem.
Here’s what I’ve done so far and some observations on testing.
I’ve isolated the problem to something after the microswitches and before the relay. Relay is not getting power, and I know this from testing.
Power is coming into the climate control switch. Climate control switch is working properly. I have tested and retested and replaced all the microswitches with brand new. All old and the new microswitches tested fine on bench testing.
Now, when I plug the green wire into the correct miscroswitch terminal I get power. With no other wires plugged in I get full power on each of the other terminals of that microswitch when the switch is set for its respective position. As soon as I plug any wire in to a terminal with the correct power setting (in other words discount that I have the selector and wire combination misconfigured), the power disappears.
So, in normal operation the green wire brings power and the pink goes to ground with the switch in the “Off” position. With the climate control switch turned “On” (that is to say to Lo, High, Defrost or Auto) the Brown wire takes power from that microswitch to the next microswitch.
In my case whenever I plug in any wire to any terminal (the pink one or the brown one) on that microswitch, Power goes from 12V to .0007 volts. I thought it might be a bad resistor, but it does it for all wires even ones that aren’t on the resistor’d line. As soon as you touch ANY wire to the terminal the power that was there a millisecond ago is gone.
I’m thinking a bad ground but don’t know enough electrics to say for sure whether that would account for the problem. Any ideas?
Again, the problem is definitely between the switch and the relays and having something to do with those wires in the harness that service the microswitches.
I’m not entirely sure I follow all of your description.
The sensing system side of the climate control is powered by a fuse in the main fuse panel.
The pink wire is powered 12 volt when ignition is on and the Climate control(cc) is switched off…Pink powers the Recirc flap vacuum solenoid with CC off to close the flaps…with CC on…pink is only powered thru a switch on the servo only in Full Cool.
With ignition on and CC on…brown wire powers amplifier and the feed to the servo fan speed micro switches. These micro switches energize the low amperage coils via the servo and then to earth… These Earth connections are fed back to the mode control switches to override fan speeds to high or low.
The high amperage fan power is fed from a separate fuse from the auxiliary fuse panel. This fuse was a Lucas fuse listed at 50 amps…unfortunately, USA fuse ratings are different than used by the British…a standard Buss fuse in the US should be rated only at 25 amps for this circuit. So it it often overused in the US which leads to a build up of heat in the circuit which can soften and distort the fuse block holder.
For Intermittent blower fans …this is the place I would start.
I need to review the wiring schematics…there are a couple diodes in the wiring harness and servo that could cause some issues if they fail.
Have you checked the climate control switch with all the micro switches screwed into position…I suspect that with use the plastic “cams” wear a little bit and possibly do not move the microswitch actuator button far enough. The micro switches test fine…but not when in position. They are very sensitive to position in the switch structure.
**
Bear in mind that when the system is in heating mode, trying to raise the temp in the cabin, muttony - the fans will not start until coolant temps reaches 41C…
This may cause intermittent ‘no fan’ situations for various reasons. Like faulty; coolant temp sensor, in-car temp sensor, temp selector, relay resistor pack, relay itself - or servo in ‘heat’ mode.
First step; check fans in ‘Def’ position whenever the problem occurs - this bypasses all the above faults…
Then you can go on a deeper search…
**
Like Gary - I read the diagram differently from you, muttony…
I don’t think the function switch is the right place to attack the problem - it is better assessed at the relay pack. First verifying that there is power on brown/white, which provides main power to the motors. A possible fault with all out fan failure is the 50A fuse - either blown or wire connection problem. Due to the high current draw, the fuse holder may overheat and melt. Causing intermittent or permanent fan failure to operate…
For further investigation; the relay pack offer easy access to all connections relevant to fan operations. And may point to a more specific areas for further testing
…which may indicate a function control fault. Interaction between the microswitches makes interpretations of testing results there very complicated - and is not the proper starting point. And a function control problem will seldom cause total fan loss…
It was the ground, Ground 7, 1984 XJ6 Vanden Plas. It looked good, but I cleaned it with sandpaper, greased it with dielectric and it immediately started working again.