How to Clean the Heat Sensor on a Lennox AC

Lennox air conditioners regulate temperature with a thermal expansion valve system, or TEV. Part of the expansion valve, located inside the evaporator, is a heat-sensing bulb. If the air conditioning unit is not producing the desired ambient temperature or refusing to settle on one temperature, the culprit may be the heat-sensing bulb. Although these bulbs generally need to be replaced, sometimes they can be restored by a simple cleaning.

Screwdriver
Aerosol electronics cleaner

Instructions

- 1
  Remove the outer casing of the Lennox unit with a Phillips head screwdriver. This will grant you access to the internal components of the unit.
- 2
  Locate the compressor, which will be a box-like component on the floor of the air conditioning system. Remove the cover of the compressor with a screwdriver.
- 3
  Locate the evaporator, which will be in a Styrofoam casing. You may need to remove both screws and spring clips. Take it out of the Styrofoam and find the thermal expansion valve, which will have a T-shaped body connected to a bulb. The bulb is the heat sensor.
- 4
  Carefully spray the heat sensor with an aerosol electronics cleaner. Do not touch the bulb, as it can be very sensitive and easily broken. Spray thoroughly and allow to dry.
- 5
  Replace all of the parts and test the Lennox unit. If it is still not functioning properly the heat sensor may have to be replaced.

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