# 4640 air cond



## mrfred (Jul 5, 2011)

What is the third wire for on the pump, plugs into the rear of the pump??? The other two wires are 12v. and ground.


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## Fedup (Feb 25, 2014)

If your tractor still has the original Delco A6 compressor those tractors came with, the third wire is for a superheat switch. The theory was that if the operating temperature of the compressor reached a certain point during use that switch would provide a path to ground for the third wire. This will effectively "blow the fuse" in the thermal limiter (the little black box with three spade terminals connected to the compressor wire pigtail). This interrupts the 12v signal and stops the compressor from operating until the system is checked and repaired as needed.


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## mrfred (Jul 5, 2011)

Thank you


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