How to adjust an expansion valve

Written by clayton yuetter
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How to adjust an expansion valve
The thermal expansion valve controls the amount of superheat inside the cooling system. (Jupiterimages/Comstock/Getty Images)

Thermal expansion valves maintain the temperature of the cooling unit inside a vehicle or external air conditioner by regulating the amount of refrigerant entering the evaporator. The expansion valve controls the amount of the system's superheat, which is the disparity between the vapour point of the refrigerant and the temperature of the refrigerant as it leaves the evaporator coil. If your unit is not cooling effectively, the expansion valve may need adjustment to change the amount of superheat in the system. The procedure for adjusting an expansion valve is the same for units found in both automobiles and external air conditioners, as the valves have the same parts and functions in all cooling systems that use them.

Skill level:

Things you need

  • Thermal expansion valve pressure-temperature chart
  • Manual for vehicle
  • Thermometer probe
  • Socket wrench (optional)

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  1. 1

    Read the pressure gauge on the suction line. Attach the thermometer probe to the same spot on the suction line and determine the temperature.

  2. 2

    Find your pressure reading on the pressure-temperature chart supplied by the manufacturer. Cross-reference what the appropriate temperature should be for that pressure with the charted temperature. Calculate the difference between your recorded temperature and the charted temperature.

  3. 3

    Locate the expansion valve's superheat adjustment stem, using the manual if necessary. Depending on the model, it may be under a protective cap that needs to be removed with a socket.

  4. 4

    Turn the valve on the adjustment stem towards the "open," or parallel direction to allow more refrigerant into the evaporator, if your system has been operating at too hot a temperature. Partially close the adjustment stem to reduce the amount of refrigerant in the system, if the unit has been cooling excessively.

  5. 5

    Allow the unit to run for 10 minutes. Make further adjustments if the superheat setting is still not effective.

Tips and warnings

  • Only make subtle adjustments before checking their effect.
  • If the system appears to be "hunting," or constantly fluctuating between temperatures, feel the compressor body to determine if more or less superheat is necessary. If the compressor body sweats, reduce the amount of refrigerant, and if it feels warm to the touch, add more refrigerant.

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