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1970-1995 Range Rover Classic
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73 Posts
Discussion Starter #1
In my '91 the A/C works fine for a while, maybe an hour or so, then I can hear rattling sound like the clutch rapidly engaging/disengaging, then the air stops being cold and if I check the compressor I can see that the clutch is not engaged.
Stupidly I never thought about checking if the electromagnet was on or not when the clutch is off....
If it rests for a while, it will work again for a while then the same problem happens again.
The system has been converted to R134 and has just been recharged - the behaviour didn't change before and after the recharge (my mechanic said "a lot was missing" but still the behaviour didn't change, and I wasn't there when he did it so I don't take that for certain).

A little bit of history: When I got the car the AC had been removed for who knows how long. Last year I refitted the compressor and the condenser, and ran beautifully, maybe even too cold! this summer I noticed this problem and asked for a recharge, but it didn't help.

Could it be something as simple as the clutch not engaging properly when hot, or can it be something more complicated? I promise next time the compressor isn't engaged when it should I will check if the electromagnet is on or off, but sadly these days I'm not using it enough to replicate the problem.

Any ideas? Too much gas pressure? too little? I only have 1 electric fan on the front of the condenser instead of the stock 2, but that's the same setup as last year and it worked.
 

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It sounds to me like an electrical issue with your trinary switch. Have you tried to just power the AC clutch temporarily and see if it works? You should be able to change the trinary switch out without loosing gas, they are cheap and I would give that a try first. Alternatively the clutch can be adjusted by adding or removing shims. If the clutch magnet is energized but it is not engaging it could be you need to make an adjustment.
 

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1970-1995 Range Rover Classic
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73 Posts
Discussion Starter #3 (Edited)
Thanks. Is the trinary switch the switch that sits on to of the AC filter?
I'll try to jerry rig power to the AC next time I succeed in replicating the problem, good idea, thanks.

Edit: I just checked and there are 2 different switches on the filter/dryer/cylindrical thing on the inner wing: they look identical. Which one is the trinary switch, or which one do you think I should swap?

edit2: and neither switch is cheap! £115 / £140 each
 

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I had a very similar issue with a P38 and it ended up being a clutch that wore itself out of adjustment. Removing a shim from the clutch assembly fixed it right up. It's a simple and free check/adjustment. Should be something looked at regularly on these older vehicles.

Hope this helps.
 

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1970-1995 Range Rover Classic
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73 Posts
Discussion Starter #5 (Edited)
Thanks. Hopefully that's all it takes. I managed to take the nut off the clutch, but I can't slide the clutch off the compressor. Any tips?

Edit: I noticed that on the clutch outer plate there are three threaded holes close the center. If I look through them I can see the compressor body, so I figured I those are for driving screws through them and force on the compressor body and extract the clutch. But I can't understand if they are M6 or 1/4", because none screws freely in, they both only make a couple of turns then become hard to turn.
 

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1970-1995 Range Rover Classic
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73 Posts
Discussion Starter #6 (Edited)
Ok, I managed to take the the clutch plate off. I had to scre the M6 screws in as far as they went, then using a spacer laying on the shaft a flat plate with holes and two M6 nuts, I was able to extract it.
Then I struggled for half an hour to extract the key from the shaft, becasue the washer can't get out with the key still in place. Then I gave up and decided that the best course of action would be to grind half a mm off the clutch plate shoulder, so that it will sit that 0.5mm closer once it's fully assembled 🤣
So I did that and tried to reassemble it all, only to find that I beat on the key too much and now the plate won't slide on the shaft all the way anymore. So I removed it again and now, the next time I'll have some time for it, I'll have to sand down the marks on the key.
This easy clutch gap adjustment has already taken me two hours and I'm not dine yet.. .and I'm not even doing t the right way...

Well at least the compressor is easy to get to.

edit: done! I managed to sand down the marks in the key, they refitted the clutch plate, found that I had ground too much so the clutch would be always closed, so I fabricated a .8mm shim from a thick washer (ground it thin the cut a slot for the key) and fitted it between the compressor body and the clutch. Now the gap is about .6mm, I’ll see if the problem comes up again.
 
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