TIP-LONG 1957206 - Caterpillar

HVAC System
Illustration 1 g03328603
(1) Compressor
(2) Condenser
(3) Expansion orifice
(4) Evaporator
(5) Accumulator
(6) Water Valve
(7) Heater Coil
(8) Engine
(9) Brake ECM
(10) HVAC operator controls
(11) A/C Switch
(12) Ambient air temperature sensor
(13) Chassis ECM
(14) Blower resistor pack
(15) High-pressure switch
(16) A/C clutch relay
(17) Blower fan motor
(18) Recirculation temperature sensor
(19) Louver temperature sensor
(20) Low-pressure switch
(21) Thermostat switch
(22) Water valve actuator
(A) High temperature, high-pressure vapor
(B) High temperature, high-pressure liquid
(C) Low temperature, low pressure liquid vapor mixture
(D) Low temperature, low-pressure vapor
(E) Coolant from engine
(F) High temperature coolant
(G) Medium temperature coolant
(H) Coolant to radiator
(J) Air from cab recirculation
(K) Air to cab louvers The HVAC system has three modes of operation: MANUAL, AUTO, and AIR CONDITIONING. The operator selects the mode of operation through the A/C Switch (11). In MANUAL mode the operator has direct control of the blower fan and heating system, but the air conditioning system is not engaged. In AUTO mode the operator sets a preferred temperature and the Machine ECM operates the heating and air conditioning system automatically. The operator still has direct control over the blower fan. In AIR CONDITIONING mode the air conditioning system is engaged but the operator still has direct control over the blower fan and heating system.Note: The HVAC system will not operate if the blower fan control is in the OFF.A/C System
The air conditioning system is activated either through operator request from the A/C switch (11) in air conditioning mode or from the machine ECM (9) when in auto mode and the ECM determines that the air conditioning should be activated.When the air conditioning system is activated, the machine ECM (9) sends a signal to A/C clutch relay (16). When the relay activates, power is provided to the A/C clutch on compressor (1). High-pressure switch (15) and low-pressure switch (20) verify that the high and low-pressure sides of the A/C system are functioning correctly. If either of the two switches detect pressures out of specifications, the machine ECM (9) receives a signal and shuts off the signal to the A/C clutch relay (16). Thermostat switch (21) monitors the temperature of the evaporator (4). When the temperature of evaporator coil drops below a specific point, machine ECM (9) receives a signal and shuts off the signal to the A/C clutch relay (16). Once the temperature of the evaporator coil raises back above the specific point, machine ECM (9) receives a signal and re-engages the signal to the A/C clutch relay (16). The process of the air conditioning system turning on and off is called cycling. When machine ECM (9) has engaged the air conditioning system, the air conditioner refrigerant begins to flow in the air conditioning system at the refrigerant compressor (1). The compressor is driven by a belt from the engine (8). The compressor is designed to change the air conditioner refrigerant from a vapor that has low pressure into a vapor that has high pressure. Also, the compressor changes the refrigerant from a vapor with low temperature to a vapor with high temperature. The increase in pressure causes the increase