840 HVAC Antifreezing Devices 1. Binary pressure switch It is used to limit pressure conditions in a closed refrigerant cycle for series / parallel logic. High - Low Pressure Settings: If the system pressure reaches impermissible levels i.e. if the pressure is less than 2 bar or if the pressure is higher than 28 bar then the compressor is switched off. This avoids its consequential damage. 2. Thermistor or Thermo sensor It is a temperature sensing device, which protects the AC systems from damage. It switches off the compressor when condensed water tends to form ice on the fins of evaporator. Thus it maintains the evaporator temperature within a specified range. A/C Relay It controls the operation of compressor relay and condenser fan motor according to the signals from the switches which detects the state of the engine and driving conditions. A/C relay operates depending upon the state of condition of following parameters: (a) Idle speed control (b) Dual pressure switch operation NOTE: If the pressure is less than 2 bar or if the pressure is higher than 28 bar then the compressor gets switched off. (c) Coolant (water) temperature switch operation (d) Thermistor (Evaporator thermal switch) operation NOTE: AC relay gets ON when the evaporative temperature is above 5.5° C and it gets OFF when the temperature is below 3.5° C.
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