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In the process of rebuilding the factory A/C on my 72 sb I replaced the missing thermal limiter with a NOS AC delco unit from eBay. Upon initial start up of the A/C, the main 25amp fuse for the A/C system blew. Figuring there was a short to ground causing the fuse to blow I began unplugging stuff till it stopped blowing the fuse, didn’t take long to narrow it to the thermal limiter. Anyway, I took my meter to the limiter and it shows continuity on all pins in all combinations. Makes sense as to why the fuse was blowing. Not being familiar with a thermal limiter, is this part defective?
This limiter is in the system to sacrifice itself in the even the compressor overheats due to low pressure/low freon. In the event this condition exists, the limiter burns itself out, sorta like a fuseabe link, causing the compressor to stop working, saving it so it can work another day.... When the limiter 'blows', it will smoke.... When you are low on freon, you must be able to run the compressor in order to charge it; to do that you can put a jumper between two of the connections that the limiter plugs in to, can't remember which two right now, which would allow the compressor to run long enough to charge it.
Thank you kansas123 your input is appreciated and makes sense. However I don’t believe my limiter is blown being I’m getting continuity at all three pins in all combinations. I’m thinking it may just be defective out of the box. Maybe I’m missing something here? I’m no electronic engineer but I do have some basic understanding of auto electric. In my mind I would think 2 of the pins would have continuity to pass the 12 volts to the compressor and the 3rd to ground.
Thanks for all your help, I believe I’ve figured it out. It appears the wiring diagram I’m using does not call out the superheat switch and it just appeared to me that, that leg coming of the thermal switch goes to ground. Apparently it goes to the superheat switch. My replacement A6 compressor doesn’t have one installed. I’m considering just bypassing it since I cut off the rubber boot connector and put a lug connector on to ground it. Bummer is I spent over $50 for the thermal switch and the wire harness section for the switch.
Last edited by 2xCorvette; Jun 4, 2023 at 09:14 PM.
I took my 73 with factory air to a Shop that repairs AC systems on classic cars. The first thing they did was delete the relay and they added a sensor that is located in the line going to the evaporator. I believe this sensor in the line turns the compressor on/off. also they told me to add a valve to shut off the hot water going to the heater core. 73 cars didn’t have one, cheap Chevrolet bean counters? My 88 Pontiac didn’t have one either!
A/C Thermal limiter
