Your original post states that fans and compressor both shutdown.
Either these symptoms are connected or coincidence.
If connected, it has to be a system power input problem…or an earth problem.
My standard approach is to disconnect the amplifier and power the servo motor independently and monitor the system response as you cycle it from cool to heat. Failure to get any response would still point to a mode control micro switch. If system responds…you confirmed good power and can then quickly determine failure of a single fan relay.
wow! thanks Guys, what a great resource this is. Sadly, I am going to be unable to get to this to check out all these leads until Sunday as I am off to a Car show all day today ( Hampton Court Concours ), which is going to be fun but not quite as much fun as sorting out the XJS. So pleased stay tuned I will be back on it tomorrow . Reference the micro switches, are these the two switched with thin wires behind the two controls? They are fixed to the radio panel? I have fitted a retro style radio and it had so much wiring, I do hope I have not damaged one of these or its wires as I recall them looking quite fragile. The sometimes working, then failing could equally be a broken wire as well as a bad earth or failing micro switch. Thanks once again, got to fly now:grinning:
The mode control is the assembly to the right of the radio. It is an assembly of 4 micro switches and a vacuum valve. (1 On-Off, 2 fan speed override switches, and defrost circuit switch and its vacuum valve.)
The switches are held in place by small bolts passing thru pairs of switches. They have been know to loosen there grip on the switches and allow the switch to shift its position and barely touch the cam lobe which activates them.
In my case, the microswitches turned out to be good, but the grounding point was bad. It is Ground 7 on the S57 diagram. That point grounds all the microswitches. That is why you check that Green wire on the On/Off Microswitch. If there’s power there with and without the the Green wire connected then the problem is not the ground. But if there is power at the Green wire only when disconnected then the problem is the ground.
If you need to replace one of the microswitches replacements are available on line. There are three different microswitches in use there. I have modern numbers for new ones and they are cheap. Don’t kill yourself trying to get oem ones.
Muttony,
I can see from Figure 1.2 of my S57 Electrical Guide that the G7 ground point is located at “Center Support Right Side (Behind Inst. Pan.).”
Do you happen to have a picture of that ground point that you can share with the list in case others encounter this problem with the heater blower motors and would like to try your fix?
I didn’t take a picture while I was there. It is located under the crash roll, immediately to the right of the Delanair box (on US models) where the windshield would touch the dash and underneath the grill where the wipers are on the outside. You take the glove box out and look at the firewall where the left side of the glove box was and you can’t miss it. Three multi-wire black ground connectors attach there. Easy to see once you have the glove box out. Very hard to get at with the glove box in.
Just before I get stuck into some more testing tomorrow, is it possible to test the micro switch on the mode without taking the centre console out? If I have to then thats fine, but I could do without disturbing the installation of my radio unit, it was a pig to fit.
And if I am testing the green terminal in the female side of the white plug, please remind me what this is establishing? thanks Guys, I am very grateful for the help with this.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
28
perfect, thanks and this comes from the fuse block I assume to the micro switch on the mode control? At present I cannot even see a green wire! No doubt after some excavation tomorrow morning I will do. I am beginning to wonder whether when I fitted the radio I knocked off the green wire from the microswitch.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
30
Your claim that applying power to the green/slate wire engages the compressor clutch still concerns me. This should be impossible. I’m wondering whether you might have a weak connection somewhere, one that reads 12V when everything is off but passes no current when loaded. Just to be sure, please conduct all voltage readings from now on with the system fully loaded, on and trying to run.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
31
Yes, Delanair did us a favor there and used standard microswitches rather than something unique. The whole point is that you can get them from any electronics supply store.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
32
Your car is right hand drive? Hmmm. I wonder if that makes a difference. The usual way to get at the control servo is by removing the knee bolster on the right side of the console.
The green wire on the female side of the amplifier plug is not a power wire…it is the wiper leg of the feedback potentiometer on the servo. The other two limits of the feedback pot are the yellow and the orange wires.
Don’t confuse the green amplifier wire with the green power feed to the system power micro switch.
Green feeds the mode control system power micro switch…then switches to brown as the power for the amplifier and splits off to the servo and it’s fan speed micro switches.
Well, having spent the whole of today on it, I am nearly admitting defeat. I am going to take a break from the problem as its driving me to distraction. I think I may need to bring in someone with a better working knowledge of Aircon electrics. I dont mind admitting that the wiring diagram is just beyond my pay grade . I cannot fathom out how it works and therefore isolate the problem area. There are so many inputs that affect each circuit its hard for me to know which is causing the problem. I have stripped down the mode switch although my instinct is that its not this. There is power to that and a good earth. Each micro switch is clicking as it is moved between positions. I did not take the switch out, call it instinct its not the mode switch. I know that fan motor amplifiers are known to fail and this is currently my best guess or the relay if I can find a diagram to help me test the relays. Thanks for all your help and I am sorry I have no better news to share with you at the moment. Some time and a change of scene will usually help!.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
35
The water temp switch is on the pipe to the heater core, behind the knee bolster on the L side of the console. Please short the wires together and report if that makes any difference.
yes I have done that. It made no difference. There is no power on the green female on the round plug by the way, but not sure that should be powered according to another poster. Brown wire is live when switched to de mist but no power when switched off on the mode switch.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
37
On your diagram above, the green wire providing power to the control system is entering the diagram at the bottom left corner. I dunno what plug you call that, but find it and tell us whether it has power or not.
yes I checked this today. It enters the mode switch and has got power there. I didn’t strip the mode switch out of the bracket as it was a load of work without me being able to convince myself that it was the problem. If the whole system needs power through the lower micro switch to work, then maybe I should have taken that out to discount it. Can anyone confirm that the electric cooling fan on the radiator comes on automatically with the air-conditioning? On my non aircon XJ12 series one it only comes on with the engine temperature to augment the viscous fan. Is it different with the XJS?
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
39
On the earlier models it does. On later models – perhaps with the switch to R-134a refrigerant – there was a pressure switch on the freon circuit that would bring it on when needed, meaning sometimes it would not come on with the compressor. IMHO, the wise owner would rewire it so it does come on with the compressor. The electric radiator fan should always be running when the compressor is engaged. Shutting it off is a fool’s economy, because while you may save power running the fan, the compressor is having to work harder because the condenser isn’t as efficient.
Since the electric radiator fan on the XJ-S also comes on when the switch in the water pump inlet elbow says the coolant coming out of the radiator is too hot, a set of diodes is provided to prevent one of these circuits from backfeeding the other. The diodes are within what looks like a blue relay, but in fact there’s no relay inside, just a circuit board with diodes on it.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
40
Andrew, I’ve put together a couple of simple tests for you to perform and get back with us. They all pertain to the yellow relay in the diagram, which I presume you can get at. There are four wires connected to it. With the ignition and the controls on, the following should be true:
The N/W wire should have 12V on it.
The N/Y wire should have 12V on it.
The B wire should be securely grounded.
If all three of these conditions are true, then the yellow wire should have 12V on it – and the blowers should be running on low speed. If the yellow wire has 12V but the blowers are not running, either the resistor pack is defective or the blowers aren’t working – and I believe you’ve already confirmed the blowers work. If the yellow wire does not have 12V, the relay is bad.
If any of those three conditions are not true, get back with us and we’ll proceed from there.
BTW, pray that the resistor pack is OK. It’s a simple device and easy to repair with some nichrome wire from an old toaster, but in the XJ-S it’s a bear to get at. I seem to recall having to drill a hole in a structural member to be able to get a screwdriver on one of the screws.
