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1973 toronado, changed out an a/c hose today, re-filled system with r-12 and oil, Has a comfortron and now the compressor won't turn on ( was working before this hose change), no power getting to it. The fuse is fine under dash and I would think the thermal switch by compressor is fine, but no power to it either, It does work and get cold when hot wired, Any ideas would be appreciated.
Do you have a 1973 Oldsmobile factory Chassis Service Manual? It dedicates 30 pages to Comfortron diagnostics, if that tells you anything.
Since it worked before the system was depressurized and opened, the first place I'd look is the superheat protection circuit. There's a pin switch on the compressor, usually on the rear compressor head. It's purpose is to interrupt power to the compressor clutch in case of a low refrigerant condition.
You'll also see a thermal limiter fuse clipped to the compressor bracket. The superheat switch causes this fuse to blow on low refrigerant charge.
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Use these pictures to troubleshoot this circuit.
With system in any position except OFF or VENT, there should be 12v at thermal limiter terminal B. If not the trouble is in the control head or ambient temperature switch.
With a properly charged system there should also be 12v at terminal C. If not, either low refrigerant charge or a blown thermal limiter fuse. Remove the TL fuse from its clip and jumper across B and C. If compressor engages, TL fuse is blown. You need to find and correct the cause, otherwise it will blow again.
If you didn't jumper the TL fuse while you were evacuating and charging the system per the note in figure 1A-5, my money says the TL fuse blew. It did what it's supposed to do.
But since the things are known to blow for no good reason and usually the hottest day of the year, just do what a lot of us do and leave the fuse out and jumper the B&C terminals.
If this doesn't correct the problem, you're going to need the shop manual. Too much to go into here.
Last edited by rocketraider; April 17th, 2024 at 05:14 PM.
April 17th, 2024, 03:05 PM
