Refrigeration Pressure Switches
Richard – What are refrigeration pressure switches used for in refrigeration circuits and how do refrigeration pressure switches protect the system from further damage?
Thanks for the question and for being a reader of High Performance HVAC! First there two types of basic refrigeration switches in the typical high grade residential system. I say high grade because not every refrigeration system in air conditioners and heat pumps have refrigeration switches to protect the refrigeration system.
High Pressure Refrigeration Switch – The high pressure switch will kill the compressor circuit if the pressure exceeds the rating on the pressure switch. These pressures will vary depending on the type of refrigerant the air conditioner or heat pump uses in the system. On some air conditioners or heat pumps this switch is manually reset only simply because if it trips there is definitely a problem that needs to be resolved before the system should run again. On Rheem and Ruud heat pumps and air conditioners the reset button is usually red on located near the control panel. A simple push of the switch will reset the switch and the operation of the air conditioner should return to normal until the pressure exceeds the rating of the switch. Things that can cause the pressure switch to trip include:
- Bad condenser fan motor
- Coils plugged up with dirt and debris
- Fins on the coils bent
- Blockage in the refrigeration system
These issues, if they exist, should be taken care of before before the switch is reset. The high pressure switch prevents the system from operating at extremely high pressures.
Low Pressure Switch – The low pressure switch is typically an automatically reset switch that will reset itself when the pressure on the low pressure side of the refrigeration systems returns to normal or above the setting on the switch. When a refrigeration system operates at lower than normal pressures the system can freeze up with the freezing beginning at the evaporator coil and working its way back to the compressor via the suction line. Freezing of the refrigeration system is bad and lead to liquid refrigerant slugging in the compressor which can lead to compressor failure. Things that can cause the low pressure switch to trip include:
- Low refrigerant charge from a refrigerant leak
- Blower motor failure in the air handler
- Plugged evaporator coils or a blockage of air flow
- Failure of a refrigeration component in the refrigeration system
Again, if these issues exist in the refrigeration system they need to be addressed to prevent the low pressure refrigeration switch from tripping.