12v signal to A/C compressor

[workmeistr]

Hi. I just decided to get my A/C refrigerant filled in the '93 LWB. We had converted to R134 about 5 years ago, and about 2 years ago it stopped blowing cold, so I forgot about it and unplugged the electrical connection at the compressor, as it wanted to spin continuously without enough R134 in the system to cycle off. The shop was able to fill, find a leak at the fill valve, and thankfully, run the system through it paces, but only by hotwiring the compressor 'on' from the battery.

Somehow over the course of two years since I unplugged the compressor, the truck now doesn't send 12v to the compressor when the A/C is selected at the dash. All other dash items seem to work, heat, fan, vent selction. Besides the fuses for A/C on the dash, which check out fine, what are the other weak links in the A/C chain to check next, relays, etc.? I can't find an electrical troubleshooting manual for anything but the '95 Range Rover, surely a much different system? Any assistance or leads is appreciated. Thanks :thumb-up:

[o2batsea]

95 ETM works for 93, at least as far as the AC goes. I assume you have the fan switch on when you have AC selected otherwise it won't do anything.
It's very difficult to offer any kind of solid info since the system has been bodged and ignored for years. It could be anything. My advice is to get out the multimeter and start testing the circuits. If the electrical is OK then the next thing is to check the expansion valve (the "brain" of the system)

[bkreutz]

I'm reaching back in my memory (which gets more suspect every year:D), but I worked at a LR dealership '99-'04 and I seem to recall replacing a lot of pressure switches on the AC systems, what it does is interrupt power to the compressor clutch if the system pressure is too low or too high, IIRC the switch is on the left side of the condenser 3/4 of the way down. Worth looking in to, Oh I just remembered, you don't have to evacuate the system, it's screwed into a fitting that has a shraeder valve.

[workmeistr]

Thanks for the leads. I'll follow up with any success, or utter failure, of the weekend troubleshooting.:thumb-up:

[workmeistr]

Upper radiator fan switch inop. I have it jumped with a 10amp in-line fuse, looking forward to replacing with a new switch.