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

New Thread for No Blower Fans

Old 04-20-2019, 04:39 PM
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Default New Thread for No Blower Fans

The Patient: 1984 XJ6 VDP
Symptoms: No blower fans at any speed, no matter what setting is selected
Facts deveoped thus far:
1) Fan Relay is working. I took this out and and tested it on the table. All relays clicked when power was applied. By this I mean that I applied power to each of the four separate relays in the consolidated relay and each clicked when it was its turn.
2) Fans work when Green/Slate is connected to the Brown and White
3) Vacuum moves the flaps when Mode Selector is turned.
4) All fuses, 35 A, 50A, 3A In-Line Grounding at amp, the other in line fuse on the passenger side next to the servo. 15A AC Fuse in pos. 12 is also new and working.
5) Only one relay clicks when the mode selector is moved and this is the relay that activates when mode selector is moved to or from the "ON/OFF" position.
6) Only Hot Air when vehicle is in motion. In other words, vacuum will control the flaps (to some degree) and only hot air flows (not I said "flows" not "blows", this is just air moving through the system. No fan noise whasoever)
7) Servos Not Working
8) System worked correctly a week ago. I changed the Heater Valve and the whole thing worked. Then it stopped.
9) When the system failed, it failed gradually over a minute or two. Meaning that it stopped working for the Hi and Lo, but Defroster continued working for a minute or two then it stopped too.

What I already know:
1) it might be the Amplifier. But if I understand correctly, the amp should only have an effect when the selector mode is set to "Auto". The Lo and Hi should bypass the Amp.
2) Fuses. Yes, I have checked them and rechecked them.
3) The fan relay. As noted, I have verified it is working and not corroded.
4) The fans actually work. I have verified that they work by jumping them.
5) The Mode Selector Switch is actually 4 Microswitches.

What I would like to know:

1) What voltages should be present at the fan relay and at which posts when the system is set to its various speeds. I would like to see if there is power to the Fan Relay. There does not seem to be
2) If you think it is the amplifier, can you explain how it powers the fan -> I thought the Amp only goes to the servo and the servo's don't send power to the fans AFAIK
3) What size battery (1.4V, 6v, 8v 12v,) should you use to jump the red and purple wires on the amplifier connector to test the servos? Does the key need to be switched on during this test?
4) Since the Fans don't work on any speed and I have been studying the wiring diagram, can someone trace power flow on the diagram when the selector is in the, say "LO" position. I am not sure I understand the diagram.
5) Would one bad microswitch on the Mode Selector know cause the whole system not to work? If so, isn't that a clue as to the cause?
6) I know these microswitches are still available commercially. Does anyone know the model number/identifier for them so I can go to Digi-Key and order 4?

It is highly unlikely I have had a catastrophic failure of many components. As I said the system worked, then it didn't. There has been no burning, popping or anything else that would indicate a sudden component failure.

Thanks everyone in advance.
Old 04-22-2019, 07:28 AM
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there are Circuit Breakers, black thingies that look like transistors above the fuse box in the passenger side. You said you heard a "clack", I believe that is how they sound when they break the circuit. Not sure if they rescucitate but I think if you disconnect the two wires to each, they do.

I might be wrong, so if I am wrong about those thingies, then I don't know what they are. Let the experts say what they are.
Old 04-23-2019, 06:16 PM
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Well, I figured it out. Turns out the problem WAS the microswitches. I pulled the mode control out and the thing looked virtually brand new. In fact, I'd guess it had been replaced before. Once I got it on a table and under good light, I was able to see that one of the posts holding the switch together was not bolted together properly. The nut had basically been put on the end of the post with barely a twist. I tightened that up and cleaned the silver contacts on the microswitches because they were filthy. You couldn't tell they were silver until they got cleaned. I put in in the car but not back in the dash to test. And it worked.

I plan on putting together a post of my troubleshooting including alot of information about those microswitches and how I narrowed the problem down to them. I also have made some diagrams for myself as to how they are connected in case someone pulls them off without marking it down. I also have some new part numbers for the microswitches (new manufacture) in case yours goes actually bad. Tips on how to test the microswitches as well as some interesting things I found out about how to jerry rig an amplifier bypass from an old window switch. Gonna have dinner and then try to put the dash back together.
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yachtmanbuttson (04-24-2019)
Old 04-23-2019, 08:33 PM
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Great job. Persistence pays off. Yes, please document it here so future Jaguar enthusiasts can benefit from your findings. This is what the forums are all about.

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