PANEL AS-DOOR 3755573 - Caterpillar

Illustration 1 g01518521
Compressor protection schematic with an on delay timer (Compressor Protection Module)
The protection system uses an on delay timer assembly for the refrigerant compressor that monitors three switches in order to protect the refrigerant compressor. The on delay timer assembly will perform the following functions:
Increase the life of the refrigerant compressor if the air conditioning system has a low refrigerant charge.
Delay the refrigerant compressor from engaging during engine start-up.
Protect the compressor clutch from low voltage and high voltage.
Illustration 2 g01508064
On Delay Timer Assembly for the Refrigerant Compressor
Illustration 3 g01512253
(1) Output (signal voltage)
(2) Chassis ground
(3) Compressor clutch
(4) Power supply When the air conditioning switch is activated inside the cab, the air conditioning switch supplies voltage to the on delay timer assembly through pin (4). If the voltage at pin (4) is outside the acceptable range, the on delay timer assembly will not engage the compressor clutch coil. If the proper voltage is present, the on delay timer assembly delays the engagement of the compressor clutch for 15 to 20 seconds after the air conditioning switch is activated. The on delay timer assembly monitors the status of three switches by sending a signal voltage through pin (1). The following three switches are monitored by the on delay timer assembly:
The high/low pressure switch on the high side of the air conditioning system
The low pressure switch on the low side of the air conditioning system
The thermostat switchThe three switches are connected in series to ground. If any one switch creates an open circuit, the on delay timer assembly detects the signal. If any of the switches cycle on and off in rapid succession, the on delay timer assembly will start a time delay. The time delay limits the cycles of the refrigerant compressor to 4 times per minute.