Thermal fuse - NOT

[PaulGover]

Just for info:
My 1986 XJ6 Sovereign Series 3 had working air-con last year, but for various reasons I committed the cardinal sin of not starting the car for perhaps 9 months, and now there's no air-con. Looking under the bonnet, it's clear the compressor clutch isn't engaging. My workshop manual (the complete paper set) leads to a wild goose chase:
1) check the thermal fuse
2) said thermal fuse is "towards the front on the RH wing valence"

No, as far as I can tell from Internet photos, it's on a bracket bolted to the compressor. But anyway, there isn't one. In my car it has been replaced with a Bosch relay (on the same bracket), a standard 30A relay as fitted in several other circuits in the car. Other sites on the web indicate that sometime around 1986 Jaguar replaced the "Superheat switch" and thermal fuse combination (a really weird and nasty solution IMHO) with a low-pressure switch and relay. If the gas has leaked out, the low-pressure switch opens (or maybe closes, I need to check), and the relay disconnects the clutch circuit.

This change must require a different compressor, as the low pressure switch replaces the superheat switch, and AFAIK the latter doesn't require a hole to connect to the refrigerant, whereas a pressure switch clearly does. I'll have to check up on part numbers.

FWIW, the compressor clutch shows signs of an oil leak; it looks like the long period without starting the car lead to the seals drying out and leaking the gas, just like the book warns. Once I've got my MOT, it's down to Halfords or somewhere for a full air-con service.

[mike020150]

Good luck Paul. I've replaced the compressor on my series 2 so many times, I've lost count. It doesn't like being left unused over winter. The seals never were much good. I believe there was, in the day, at least one GM model which had an additional shield around the clutch designed to catch the oil leaks and avoid owners making warranty claims! Mike.

[poprivet]

The problem is not knowing what changes and modifications have been done over the previous 37 years, It's unlikely to be still using R12 gas or the original compressor any more.

There's not much the unqualified person can do on an A/C system these days so it's really a case of getting a trusted garage to fault find and rectify the problem. I used to work on mine but once R12 was phased out I sold my guages and gave up.

[PaulGover]

The problem is not knowing what changes and modifications have been done over the previous 37 years, It's unlikely to be still using R12 gas or the original compressor any more.
...

I'm in luck, the previous owner was meticulous about maintenance and servicing. The car had an annual service despite doing only around 1000 miles a year. The engine bay is full of stickers, so I know it's been converted to R134a by someone who knows what they're doing. So it's just a small matter of finding a decent AirCon expert at a sensible price.