Repair Airconditioning- S3 4.2 Sovereign

(Aristides Balanos) #21

It’s part of the footwell black vent cover.

(Con Saris) #22

Hi Back again, I have now tested the servo operation firstly on the LHS octagonal plug which yielded no servo operation and then on the RHS which also gave me nada. I removed the servo which was reasonably easy except for the vacuum hoses pulling off before I had a chance to mark where they came from. I will deal with that at reinstallation time. I have the servo on the bench. I checked that power was getting through to the little circuit board on the motor which it was. I tried turning the motor cog manually and it seems fairly free moving. I did not turn it a lot, being a little wary of over turning it in the wrong direction. I have checked the components on the circuit board that I can reach easily namely the two diodes and the two white components that may be low value resistors and they seem ok but not sure as they don’t actually look like resistors except in shape. Does anyone anyone know what those two components actually are? I also checked the micro switch on the end of the servo which also checked out ok. Not sure where to go from here.

(Con Saris) #23

The diodes checked ok in circuit but as we know its better to check these with one end disconnected. I will do this later and report back.
Just desoldered both diodes. The one closest to the edge of the board cracked its casing but measures ok and the other measures high in both directions. Are they both just normal diodes? Might as well just replace both of them. Will 1N400x do the job?


(Frank Andersen) #24

Have you tried checking resistance through the motor itself, Con - the problem may be a burnt-out motor…?

xj6 85 Sov Europe (UK/NZ)

(Con Saris) #25

Hello Frank, I hadn’t checked the motor resistance but just did, it measures around 16 ohms. Is that high? I’m not sure. I also just had a look at the S57 which shows the general layout of the components and the white components that I couldn’t identify were shown as inductors. They checked out ok. I have also just replaced the diodes with 2 new 1N4007 diodes did not make any difference.
How many times would I need to manually turn the motor gear before it started to turn the other gears and which way? Just wondering if I need to turn it away from its limit to get it going. Is the motor hard to remove? Seems like a fairly complicated gearing system.


(Aristides Balanos) #26

Hi Con,
16 Ohms is not high.
Can’t you connect the motor directly to a 9 or 2V source to see if it’s working ok ?
Mark the cam’s initial position before you try though.

(Con Saris) #27

Do you mean 9 or 12V? I have an old 12V car battery that I’ve been using for testing. Its ok just can’t supply cranking amps any more. Its dark out now but will give it a go tomorrow.

(Frank Andersen) #28

I agree with Aristides, Con - 16 ohms imply some 0,75 A at 12V. But more importantly; it shows continuity through the motor. However; it is very important that the motor terminals are disconnected from other circuits to avoid a false reading…

You may try connecting the motor terminals to some 3 - 4V as a ‘safe’ back-up test - to verify motor function…?

It is indeed a very complicated gear train - intended to slow the high motor rpms to the more sedate rotation of the servo camshaft - and for power and precision cam setting. It takes about 30+ seconds for the servo to travel extreme to extreme.

The gear train is somewhat frail - but camshaft movement should start immediately the motor turns, no slack. Turning the gears to move the motor…handle with care.

Overall function; feedback pots are operated by the camshaft. Telling the AC amp that the intended camshaft position is acquired - and cuts motor power. The function of the circuit board are more uncertain; no cap or diode dimensions or identified board locations are given. But the capacitors are likely there to prevent arcing in the microswitches. The diodes prevent unwanted feedback - so their polarity is critical. The only ‘safe’ replacement method is ‘like for like’ (or equivalent), which is difficult without original markings. But I don’t ‘think’ dimensions are critical - beyond a rating of some 16V…?

You are really into nitty-gritty, previously not addressed in the forum - so your feedback is welcome…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

(Con Saris) #29

I"ve had a closer look at the motor connection to the circuit board. I dont think that I’ll be able to get the board of with the motor in place. I managed to get power to the motor connections with no response at all. It looks like the motor is kaput. Is it worth me pulling the gearbox apart so I can remove the motor. I can’t find a part number for the actual motor although IF I can find a motor of the correct physical size that is reversible and has the screw holes in the correct place AND moves at a reasonable rpm will that be enaough to bring the servo back to life? I have seen a couple of used servos on fleabay but I guess you take your chances there. Does anyone have any thoughts on all this?

(Gary Crosby 75 XJ6L, 85 XJ-S, 09 XF Supercharged.) #30


If you want to remove the motor…you will have to dissemble the gear box. To do that…the face plate is attached to the base by 2 screws and the secondary plate by several brass stand offs. The face plate keys to the brass stand offs which are then expanded to prevent removal. You can drill out the end of the standoff with large drill ~1/4 inch (6.35mm) diameter. This will allow the face plate to be prayed off. You will need to drill and tap the brass stand offs and re-secure the faceplate with screws. I usually tap 6-32…3.5mx.6 …pay close attention to position of each of the gear sets…they can get easily confused making reassembly difficult.

Any similar spec’d motor should work.

Not knowing how you did your motor testing…I offer that one of the motor limit switches could be faulty. The limit switches are the first 2 in the top row of switches toward the gearbox end. If I remember right they are normally closed switches.

I think the challenge will be removing the motor gear and finding a motor with appropriate shaft dimensions.

I have no experience with ebay servos…but I think they would have to test and confirm motor, switches and feedback pot operation before paying any significant amount.

I hope it is not a faux paux…but I offer refurbished servos thru my website.



1 Like
(Con Saris) #31

No faux paux on my behalf I was going to ask if anyone could recommend a supplier. Might check out the limit switches first though. I will email your company if I decide to replace the unit.

(Con Saris) #32

Hi Gary, Just checked those two switches. Both check out ok and you were right those two were noemally closed. Checked the other switches while atg it gthey are all ok. The terminals of these switches were a bit grubby so gave them a bit of a clean before reattaching the plugs. Still no joy. I think Im coming to a point where a decision is going to need to be made. Unless anyone has any other ideas it may be time to replace the unit.

(Frank Andersen) #33

I think getting a replacement is pertinent, Con - its the simplest way forward…

The servo is very reliable - so odds are that a used unit will be in working order. You may then compare them and assess options…?

It’s a bit strange; with resistance tested through the disconnected motor - ‘something’ should happen, if only plain heating. While testing; you could use an ammeter in series to check current drawn…?

xj6 85 Sov Europe (UK/NZ)

(Con Saris) #34

Hi Frank,
Yes I have decided to bite the bullet and buy a refurbished unit from Jag-aire. Prices are reasonable compared to and untested ebay second hand unit. Will follow up once thats all taken care of.

( #35

Hello Doug
Several minutes ago I posted an item regarding my 1987 series 3 XJ6 a/c malfunction. I took the car to a shop I’ve worked with for years, but, at this point, I am seeking more advice. I did not like the fact that the shop owner told me if he gets a new compressor for me it would be $800.00 JUST FOR THE PART. I asked him what brand he would use and he could not answer, saying he’d have to ‘look around for one.’ I suspect he’s looking at one of those ‘flat rate’ books to calculate what he could charge, though he did say if I wanted to shop online for a replacement compressor he’d be ok with that & just charge me for labor, but said if I brought my own compressor he would not give a warranty on it. When he examined my car today he said the problem with my compressor is the clutch is worn and showed me the pulley is further away from the compressor than it should be. The good news is he saw that my compressor seems to not have lost regrigerant, which means it can be re used. I asked him if he could possibly just replace the clutch on my old compressor in situ, but he sad the compressor must be removed from the car to do that, as it is he claims replacing and compressor and charging the system is at least a three hour job. Do you have any thoughts on this? If so, please do let me know. Thanks
Mel R.

(Frank Andersen) #36

That work time is not unreasonable for the full Monty, Mel…

xj6 85 Sov Europe (UK/NZ)