Hot Gas Bypass Valves

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  • When using an R‐22 Replacement always adjust the minimum pressure set point accordingly.


Hot Gas (Discharge) Bypass Valves limit minimum evaporator pressures under low load. By limiting the minimum evaporator pressures the system prevents coils from frosting and ensures proper oil return in low load conditions.

Hot gas bypass valves are designed to provide a false load on the evaporator coil by bypassing hot gas from the discharge line to the evaporator. The false load helps maintain an operating suction pressure within the equipment’s design parameters and can also help prevent compressors from short cycling.

There are several different ways hot gas bypass valves can operate but they are typically controlled by temperature (utilizing a sensing bulb) or by suction pressure – either type should be adjusted to the replacement refrigerant pressures. Refer to OEM recommendations for appropriate temperature setpoints but in general hot gas bypass valves in most air conditioning applications should be fully engaged at 28 F (frosting temperatures will vary with load, airflow and system operation).

Best Practices

  • Adjust hot gas bypass to appropriate pressures. For TdX 20: 28 F evap. = 36.8 psig dew
  • Some older hot gas bypass valves are non‐adjustable; refer to OEM or contact Bluon Tech Support.

Additional Tips

  • When using blends, some frosting may occur on distributor and/or evaporator inlet due to refrigerant glide.
  • If significant frosting occurs, confirm proper charge and increase pressure setpoint.


Figure 1. Sporlan Discharge Bypass Valve.