The blower motor on my 1985 XJS only works on Low Speed, regardless of whether I select auto, high or defrost.
1. When I go to from off to low,auto, high and defrost, the servo WHIRRS and I can see the mechanical action of the linkages.
Question: Should the servo operate when switching from LOW to the other modes? If so, then that portion of the system is OK.
2. When I change the temperature control I also hear the servo WHIRRING and I can see the mechanical action of the linkages.
I then went to the main relay. I jumped the main terminal(the one with the screw) to each terminal of the individual relays within,
and the blower motors respond with the different speeds. (Blower motors are good)
Could the problem be the Mode Switch? Or is it the Main Relay?
What checks should I perform before I condemn the Mode Switch or the Main Relay?
I have a spare Mode Switch, but I am hoping it may be something else before I replace it.
Thanks in advance for your inputs.

 

Yes, because the switches on the servo trigger the different fan speeds, in response to the mode switch.

Er…...at least I think they do. I don't have my diagrams in front of me that the moment



Good !


I'll try to get back to this later tonight...if nobody else answers in the meantime.... when I have the diagrams to look at.

Do you have the S57 Electrical Guide? Or the Delaniar Manual?

Cheers
DD

 

Doug
I hesitate to disagree, and I could be wrong, obviously, but I am pretty sure the fan speed is not controlled by the servo, but by the amplifier (or some combination of the amp and the switch) in conjunction with the funny resistor thingy (RTC677) with the spiral wires on it and the big relay thingy - or maybe all the above.
If the fan will only work on one speed, then I am pretty certain that either (i) the resistor thingy has a broken spiral wire/and or (ii) the big relay pack has given up. Also check as it is possible that one of the two blowers is not working at all.
Great news that the cam unit is whirring, this means, with luck, that it is working properly.
Bad news for the OP is that if it is the resistor unit thingy, the aircon unit has to be removed from the car to get at it.
The good news is that the very complex relay pack that is accessible and can be changed (relatively) easily.
The relay unit looks like this:


The Great Palm is good on the resistor thingy, but I also attach a fuller explanation of the system which I think will help the OP sort out the unit.

 

@ Doug: I have the S57 Electrical Guide. I had downloaded the Delanair Manual a while ago when I was doing the AC diagnosis on my Series 3. However during that time my PC crashed and I lost many, many files. For the past year I have been trying to put my files on my new PC with backup on a stick.
@ Greg: Where is that resistor thingy located? I am hoping its not that.
I think what Doug was saying was that the servo responds to inputs from the Mode Switch not that the fan speed (Mode Switch)is controlled by the servo.
I will look at the S57 Electrical schematic later to see what I can figure out.
I am hopeful that there are some connectors within the AC circuitry that need cleaning. (Wishful thinking)
When I first got to checking out the electrical system. most system circuits were dead. Starting with the fuse boxes, I cleaned the spring contacts and replaced all of the fuses with new ones.
Using the S57, I started going through the various circuits and they slowly but surely started coming back to life. A very slow process but I am checking them off one at a time.

 

Greg, I downloaded the file you attached but I am unable to view the electrical images. All of the text is there but it just shows "Images) in parenthesis. No clickable function.

 

It's tricky

The default fan speed is "Low".

The amplifier is a brain that send commands (forward or reverse motor rotation) to the servo. The servo has the switches which trigger relays for Hi, Med 1, and Med 2 fan speeds.

The relays send voltage to the curly wire segments of the resistor....the varying resistance thru the segments changes the fan speed.

Manually selecting "Hi" on the mode switch bypasses the switch on the servo.

Manually selecting "Lo" prevents the Med 1, Med 2, and Hi relays from operating by de-grounding them. I think .



Cheers
DD

 

Agreed, Doug; but I think that if the big black relay thingy (see my pic above) is duff, that could be at least one of the reasons that could cause no higher-speed fans. Also, I think, open to correction as always, that if a curly wire is broken on the resistor thing, that will also result in loss of a fan speed?

 

The pdf opens Ok for me, so I have no idea why it does not for you, sorry. If you pm me your email, I will send it to you by email, maybe that will work?.

 

Greg: Will send PM but which Greg are you?

 

Yup !

But.....
I think we can assume the curly wire resistor is OK because Sanchez said he was able to get the various fan speeds by jumping the relays. Everything upstream of the resistor still suspect, IMO.

The relay pack might be OK. It depends on how the relays were jumped. On the trigger side or the output side.

By the way, has anyone ever opened up the relay pack? I suspect many internal faults would be DIY repairable.

Cheers
DD

 

I did, when I changed one out on a friend's car recently. There are four actual relays inside and all sorts of tiny copper single filament connections between them. Quite beyond me!

 

And that's the best place to start in tracking down this blower speed problem: poor connections. By checking a repairing any suspect connections you may well fix the problem and, besides, any further diagnosing may not be conclusive if the connections are not "known good".

The Delanair system is a real brain tease. At least for me.

Cheers
DD

 

???

 

Greg: I went to send you the PM I went to "SEND NEW PM" typed in Greg and it came up with a list of Gregs with their last name. I do not know your last name.

 

Greg: I sent PM. (I think) please confirm receipt.

 

@ Greg: Thank you. The emailed PDF opens up fine.

 

Just because.

All 4 of my S2 cars, and the 2 XJS's had similar issues.

NO Internet then.

I removed the radio, both control knobs, then the trim panel, CAREFULLY, and found 2 SMALL screw heads that hold that cam assembly together behind the Mode switch. The heads are visible under the trim panel.

Reached into the radio opening and felt the nyloc nuts on the other end, and there was looseness. Tightened them, FUN, NOT. and everything came to life.

My belief is the looseness caused the cams to "not quite" do as required.

They only tightened 1/2 to 1 turn, and STUPID tight is not needed.

Most other issues I have had over the years was the amplifier/brain unit.

 

Lots of rain here this weekend. I spent part of yesterday clearing the garage of all the extra XJS parts I have so I can push the XJS into the garage to do some work.
Since the car does not run at this point in time, how limited am I in diagnosing and repairing the blower issue.
DUMB QUESTIONS:
Can I use a vacuum pump to verify that the flaps are opening and closing in response to the mode and temp switch?
Can the vacuum side of the system affect what the electrical side should do? Can the tests on the electrical side be done independently of the vacuum side?

 

Oh boy, I need a beer, a BIG one.

Yes, a vac pump from the larger hose in the engine bay, below the brake booster (on the LHD cars) could simulate what you want.

ALSO

Up behind your instrument cluster, there are the 2 cooleant pipes taht feed the heater core, found them GOOD. One has a Temp Pad Switch attached with 2 wires. This Temp switch basically stops the system doing its thing until teh coolant reaches a set temp.

The fact you have SOME activity indicates someone has probably joined those 2 wires together, as we all do, thus enabling the system to work.

BUT

Somewhere in my fuzzy head I remember reading that some markets, and the USA usually falls into "some markets", has a partial feed to the system when stone cold, but that is pure memory only. Anyway, join those 2 wires, eliminate the guess work forever.

That PDF should answer the question of the Vac and Electrickery working together, but there are electric solenoids on the LH side, so maybe it does. Its been too long since I ventured into sorting one of these.

 

I suspect many cars have the wires permanently joined, yes

The idea of the switch was to prevent the system from operating at all, if heating was called for, until the coolant was hot enough to actually heat the air. This prevented the cabin occupants from having cold air blowing on them when they wanted heated air.

The amplifier ignored the switch input if cooling was called for or if Defrost was selected

On Series III sedans at least there are two test leads behind the console cheek panel that can be used to bypass the switch. You can see the wires dangling in this pic; they have grey connectors




In this case, since one fan speed is operational, I think we can take the temp switch out of the equation. But, bypassing it is easy and it couldn't hurt to eliminate all variables

Cheers
DD