Systems Operation
Air Conditioning and Heating R-134a for All Caterpillar Products
Heating and Air Conditioning Control System
Adjustable Thermostat
An adjustable thermostat contains two temperature control knobs. The temperature control knob for the air conditioning system is connected to an adjustable thermostat. A thermostat is a switch. Changes in the temperature will open the thermostat. Changes in the temperature will also close the thermostat. When the temperature control knob is in the OFF position, the electric circuit that connects the adjustable thermostat and the magnetic clutch is OPEN. In the OFF position, the compressor does not operate. The temperature of the air and the position of the temperature control knob determines if the switch is CLOSED. When the switch is CLOSED, current moves through the thermostat to the coil assembly in the magnetic clutch and the compressor operates. The temperature of the air through the evaporator coil is monitored by a capillary tube that is placed between the fins of the evaporator coil.
The temperature control knob for heating is connected to the heater control valve. The temperature of the cab is maintained by the position of the air conditioning and heating temperature control knobs.
Nonadjustable Thermostat (Freeze Control System)
Illustration picture at above
A nonadjustable thermostat contains one temperature control knob. The temperature control knob is connected to the heater control valve, which controls the flow of coolant through the heater coil. The temperature of the air across the evaporator coil is preset by the nonadjustable thermostat. The temperature of the cab is maintained by the position of the temperature control knob on the heater.
Condensation that is frozen will restrict the air flow through the evaporator coils. The compressor will continue operating only if the condensation does not freeze. In order to prevent the condensation from freezing, the thermostat switch opens at a temperature of approximately -1.1°C (30°F). Also, the thermostat switch closes at approximately 2.2°C (36°F). When the switch opens, the electric circuit that connects the switch to the magnetic clutch is OPEN and the compressor does not operate. When the switch is CLOSED, the current moves through the switch to the coil assembly in the magnetic clutch and the compressor operates.
In order to operate the system in the correct manner, the heater core supply must not be closed. Also, in order to operate the system in the correct manner, the return coolant line valve must not be closed.
