Kaspar

Maybe some of you have tinkered on mentioned models' AC systems, mine is 87 924S, but the system should be roughly the same as early 944.

Backstory:
My AC hadn't worked for over 10 years. P/O told that condenser is bad so I removed and pressurised it under water, found about 10 leaks, all from corrosion probably.
At this point I decided to do R12 -> R134a conversion. Along with new condenser I also replaced receiver drier, 6 out of 8 O-rings (apart from those under dashboard), refilled compressor with ester oil (120ml) and added low side R134a adapter to compressor, high side adapter next to receiver drier.
I took the car to AC shop and testing showed no more leaks, in went 770g of R134a.

Problem:
AC compressor clutch coil doesn't get any power.
*I tested the low pressure cut out switch next to receiver drier with both wires still attached - both leads have 12V, so the switch is good.
*I jumpered wire from battery to compressor, switched AC on and it started blowing ice cold, so compressor and its clutch are also good.

Does the wire from low pressure cut out switch go straight to compressor clutch coil? From the below diagrams (PDF attachment) It seems so, but there's also a diode in parallel.
Could I just run new wire from switch to compressor or is there anything else to check?

orig944

The schematic shows a wire connecting them with no intervening connectors, so it is corroded or broken somewhere along the way. At the connectors would be a good place to look first. The diode is called a flyback diode, and is there to extend the life of the low-pressure switch. I'd keep it in the circuit if possible. Oddly, I do not see one on the pre-85.5 schematic, so now I think I will be adding one to my car.

The ester oil will cause the two remaining Buna-N o-rings to eventually fail.

Kaspar

Thank you orig944, very good info. I routed new wire and cut off the old one to prevent it from grounding somewhere, diode was left in circuit. The 2 remaining O-rings are holding, but every single compressor O-ring leaked soon after. There is good video on Youtube for resealing our compressors, took me ~4h with removal and installation on car.



I just had 4000 mile European trip in hottest weathers and the AC works great now. air temps from vents range from 9-16°C between cycles which I'm happy with.