fragmare

So, my thermal protector for my A/C compressor finally gave out and lost continuity a while back, and I'm getting around to replacing it. Luckily I had a pile of leftover compressor parts from doing rebuilds in my garage. I decided to dig one of the thermal protectors out from a spare compressor housing and use it in my compressor since it looked in decent shape and tested fine with a multimeter. After removing it from the housing (not easy!), but before installing it my compressor, I decided to attempt some science... I got curious and wanted to see what the cutoff and cut-in temps were for this thing. I positioned the thermal protector in a vice and applied heat to it with a heat gun while measuring its temperature with a laser thermometer. I was rather surprised by the results!

Cut-out temp: ~70C/158F
Cut-in temp: ~60C/140F

I repeated this 5 or 6 times just to verify the results, and came up with the same numbers every time. I would have thought the cut-out temperature to be considerably higher... more like 100C/212F, but I guess that's not the case. Anyway... didn't take any pics for this little test, but I'd still like to share the info.

CandyRedRC46

Cool, I have always wondered about this. My AC used to cut out when I was parked and idling on hot summer days for a long time. After changing out my header I haven't experienced an AC cut out since. I guess the ceramic coating is really helping and or the primaries are a little further away from the compressor now.

fragmare

Yea, the thermal switch can totally be influenced by outside sources (like a really hot header). I autopsied the old switch, and it's just a cheap little plastic thermo switch with an o-ring and a copper jacket around it. That's it. It looks essentially identical to some of the thermal cutoff switches found in household appliances like driers and water heaters.