R-134a Refrigeration System Controls, Instruments and Protection Devices

Compressor Discharge Line Temperature Sensor: The controller uses the compressor discharge line temperature sensor to protect the compressor from excessively high operating temperatures. If the discharge gas temperature rises above 148 C (298 F):

  • Unit stops immediately; controller activates Alarm LED and records Alarm 146, Compressor 2 Temperature Too High.

  • Controller will restart the unit when the sensor temperature is below 138 C (280 F).

High Pressure Cutout (HPCO) Switch: If the compressor discharge pressure rises above 2410 ± 68 kPa, 24.1 ± 0.68 bar, 350 ± 10 psig, the high pressure cutout opens to interrupt the ground circuit to the compressor contactor:

  • R-134a compressor STOPS immediately.

  • Evaporator and condenser fans continue normal operation.

  • R-23 compressor stops.

  • R-134a compressor will restart when the overload condition is corrected (switch closes) as long as power is available. The high pressure switch resets (closes) when the pressure drops to 1640 ± 68 kPa, 16.4 ± 0.68 bar, 238 ± 10 psig

  • R-23 compressor will restart 30 seconds after R-134a compressor restarts.

Suction Pressure Gauge: A suction pressure gauge indicates the refrigerant pressure in the suction line returning to the compressor.

Discharge Pressure Gauge: A discharge pressure gauge indicates the refrigerant pressure in the discharge line leaving the compressor. Operating Instructions 49

Receiver Tank Sight Glass: A sight glass on the receiver tank contains three small balls that indicate the level of refrigerant in the tank for checking the refrigerant charge. A moisture indicator in the sight glass changes color to indicate the level of moisture in the system. Check the color of the indicator against the color decal in the sight glass. The dry eye in the sight glass is LIGHT GREEN when the system is dry and YELLOW when the system is wet (contains excessive moisture).

Fusible Plug For High Pressure Relief: A fusible plug is installed in the R-134a receiver tank to avoid excessive pressure build-up within the refrigeration system from extraordinary and unforeseen circumstances. The plug blows when the plug temperature reaches 100 C (212 F). The plug is located so that refrigerant pressure expelled from the valve would be directed away from anyone servicing the unit. The plug is non-repairable and requires no adjustment. If the plug blows, recover the remaining refrigerant charge and replace the fusible plug.

Compressor Oil Sight Glass: A compressor oil sight glass indicates the relative level of compressor oil in the compressor sump.

Parent topic: Unit Operation