11
10 Expansion Valve Troubleshooting
Before replacing an expansion valve, check the following items:
1.
Bulb location
: Must be tightly secured to the suction line upstream of the equalizer connection.
2.
Insulation
: Bulb must be properly insulated.
3.
Equalizer
: Must be connected to the 1/4” SAE connection on the suction line.
4.
Charge
: Ensure the system is properly charged. There MUST be a minimum of 10°F Sub-Cooled liquid at the
valve inlet.
If the system appears to be “starving” (low suction pressure but insufficient cooling):
1. Check the Superheat (SH) at the evaporator outlet. If SH is between 5°F - 12°F, the TXV is controlling
properly.
-Verify that there is proper airflow to the evaporator (fan is operating and filter is unrestricted).
2. If SH is above 12°F, the setting of the TXV may be too high.
- Adjust the SH by turning counter-clockwise to decrease SH.
- Wait 20 minutes for the system to balance and adjust again, as required.
- If adjusting the valve has no effect on the SH, the valve may be stuck because of dirt or debris or it may
have lost the Power Element charge.
i. i. After properly reclaiming the refrigerant, remove the TXV and check for dirt and debris.
Clean, if possible, or replace the TXV and filter/drier.
If the system appears to be “flooding” (compressor frosting or moisture is condensing at the suction
connection):
1. Check the SH at the evaporator outlet. If SH is between 5°F - 12°F, the TXV is controlling properly.
2. If SH is less than 5°F, the SH adjustment may be too low.
- Adjust the SH by turning the adjustment stem clock- wise to increase the SH.
- Wait 20 minutes for the system to balance and ad- just again as required.
- If adjusting the valve has no effect on the SH, the valve may be stuck open because of dirt or debris or
moisture in the refrigerant.
i. After properly reclaiming the refrigerant, remove the TXV and check for dirt and debris. Clean,
if possible, or replace the TXV and filter/drier. Add a moisture indicator to allow checking of
moisture if this is believed to be a probable cause.
