Lennox XC25 – Top Cap Switch Operation, Checkout and Status / Error Codes


Top Cap Thermal Sensor Switch (S173)
Some units are equipped with a compressor-mounted normally closed temperature switch that prevents compressor dam­age due to overheating caused by internal friction. The switch is located on top of the compressor casing. This switch senses the compressor casing temperature and opens at 239-257°F to shut off compressor operation. The auto-reset switch closes when the compressor casing temperature falls to 151-187°F, and the compressor is re-energized. This single-pole, single-throw (SPST) bi-metallic switch.

Using a multimeter set to ohms, with the terminals disconnected from the system, check the resistance between the two terminals of the top cap switch. If the resistance reading is 0 ohms, the switch is closed.



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