LINK AS-TRACK 8E4326 - Caterpillar

Air Conditioning High Low Pressure Switch
Illustration 1 g01506776
Schematic symbol and drawing for the high low pressure switch
The High Low pressure switch is used in order to monitor the refrigerant pressure that is coming out of the discharge side of the refrigerant compressor. The pressure switch prevents the compressor from operating when the pressure in the discharge line exceeds a specific pressure range or when the pressure in the discharge line fails to maintain a specific pressure range. This switch is electrically connected in series with the magnetic clutch for the refrigerant compressor, and the evaporator coil thermostat. Similarly to the thermostat switch, the compressor will not operate when the High-Low pressure switch is OPEN. When the High-Low pressure switch is CLOSED, the current moves through the switch and through the coil assembly in the magnetic clutch. This causes the compressor to operate.The High-Low pressure switch has two pressure set points that will cause the switch contacts to OPEN. For a low pressure condition, the switch contacts will move OPEN whenever the pressure value for the discharge line decreases to less than 170 kPa (25 psi). The switch contacts will remain in the OPEN position until the pressure value increases to 275 kPa (40 psi) or more. For the high pressure condition, the switch contacts will move OPEN whenever the pressure value for the discharge line exceeds 2800 kPa (405 psi). The switch contacts will remain in the OPEN position until the pressure value decreases to 1750 kPa (255 psi) or less.Air Conditioning Low Pressure Switch
Illustration 2 g01506713
Schematic symbol and drawing for the low pressure switch
The Low pressure switch is used only in applications for the machine that also use the compressor protection time delay relay. The Low pressure switch is used to monitor the refrigerant pressure that comes into the suction side of the refrigerant compressor. The pressure switch prevents the compressor from operating when the pressure for the suction line fails to maintain a specific pressure range. This switch is electrically connected in series with the compressor protection time delay relay, the high low pressure switch, and the thermostat for the evaporator coil. The compressor will not operate when the Low pressure switch is OPEN. When the Low pressure switch is CLOSED, a ground signal is sent to the compressor protection time delay relay. A CLOSED low pressure switch indicates that the pressure for the suction line is high enough to allow the refrigerant compressor to operate. The compressor protection time delay relay will then turn on causing the compressor to operate.The switch contacts on the low pressure switch will move OPEN whenever the pressure value for the suction line decreases to less than 34 kPa (5 psi). The switch contacts will remain in the OPEN position until the pressure value increases to 104 kPa (15 psi) or more.