This IS the problem. These sn's you are describing are pulling the compressor clutch as well as the blower motor through the switch!!! The red wire to the switch is power in; grey, brown, and orange are speed wires, the other wire, usually black, goes to the thermostat then the lp switch - then the clutch. Too much for the switch. Therefore,either remove the wire to the thermostat -"c" on switch- and put it on a SEPARATE wire to the fuse panel with a switch on it to power the clutch through the thermostat, or just run a switched ( hot when key is turned on) 12V wire to the thermostat . In this case remember you have to turn off the thermostat to turn off the compressor when you use the heater. (duh, or in some humid conditions such as harvesting in a downpour at 33 degrees ((F- Rolf -not C )) you might find it helpful) If you want another 200 RPM or so on a hot day out of the cab blower motor, wire in a relay so as when the switch is turned to high the high speed wire energizes a relay which connects a n 10 or 12 wire you run to the fuse panel to the motor. This takes all the load off the switch on high speed where the amps really flow. The early AirCooled units had a separate switch to the thermostat. Some genius decided they didn't need it any more. Small item but when your fan switch can be used for a cigar lighter on a hot day - it ain't so small huhIJ This small tip which takes only about 15 minutes will really make a big improvement. In fact we have one customer who's reattached testicals still have frostbite damage.