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| Illustration 1 | g06415573 |
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(1) Compressor
(2) Condenser (3) Expansion orifice (4) Evaporator (5) Accumulator (6) Water valve (7) Heater coil (8) A/C compressor motor (9) Machine ECM (10) HVAC operator controls (11) A/C switch (12) Condenser fan relays (13) Condenser fan motors (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 and heating system.
Note: The HVAC system will not operate if the blower fan is in the OFF position.
The air conditioning system is activated through operator request from the A/C Switch 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 sends a signal to the A/C clutch relay (16). When the relay activates, power is provided to the A/C clutch on the compressor (1). The 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 the switches detect pressures out of specification, the machine ECM receives a signal and will then shut off the signal to the A/C clutch relay. The thermostat switch (21) monitors the temperature of the evaporator (4). When the temperature of evaporator coil drops below a specific point, the machine ECM receives a signal and shuts off the signal to the A/C clutch relay. Once the temperature of the evaporator coil raises back above the specific point, the machine ECM receives a signal and re-engages A/C clutch relay. The process of the air conditioning system turning on and off is called cycling.
When the machine ECM 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 hydraulic motor. The compressor is designed to change the air conditioner refrigerant from a vapor which has a low pressure, to a vapor which has a high pressure. Also, the compressor changes the refrigerant from a vapor with a low temperature, to a vapor with a high temperature. The increase in pressure causes the increase in temperature.
The refrigerant is sent through the condenser coil (2). In the condenser coil, heat is transferred from the refrigerant to the outside air. The refrigerant changes to high pressure and high temperature liquid. The heat is transferred by three condenser fan motors (13). The condenser fan motors are activated by the machine ECM when the ECM sends a signal to the two condenser fan relays (12). The condenser fan motors are activated whenever the air conditioning system is active.
From the condenser coil, the refrigerant moves to the expansion valve. The expansion valve restricts the flow of refrigerant and causes a pressure drop in the refrigerant. The pressure drop causes the refrigerant to change from a high-pressure liquid to a low-pressure mixture of liquid and vapor.
The low pressure and low temperature refrigerant moves to the evaporator coil. While the refrigerant is in the evaporator coil, the refrigerant absorbs heat from the air flow. The refrigerant changes to a low pressure and low temperature vapor.
From the evaporator coil (4), the refrigerant moves to the accumulator (5). The accumulator acts as a receiver dryer. In the accumulator, moisture is removed from the refrigerant by and internal desiccant. The accumulator also stores a small amount of refrigerant to adapt to changing system needs.
The refrigerant returns to the compressor as a low pressure and low temperature vapor where the cycle begins again.
the heater system operates using coolant from the engine (E). The hot coolant from the engine circulates through the heating system. The coolant flows from the outlet valve from engine cooling system, through the water valve (6), heater coil (7), and back to the return valve for the engine cooling system. The heating system is controlled by either the machine ECM when in auto mode, or the temperature control knob on the HVAC operator controls (10).
In auto mode, the ECM monitors the recirculation temperature sensor (18) and louver temperature sensor (19) to determine how much engine coolant flow is needed. The ECM uses that information to send a signal to the water valve actuator (6) which varies the opening of the water valve.
In manual or A/C mode, the heater system is controlled through the HVAC operator controls. With the temperature control knob in the maximum cold position the water valve is closed. The CLOSED position prevents the flow of coolant into the heater coil. When the control knob is moved away from the maximum heating position, the heater control valve begins to open. As the control valve opens, coolant flows from the outlet valve for the engine cooling system through the heater control valve and into the heater coil. As the hot coolant flows through the heater coil, the temperature of the air that is flowing through the coil increases.
The temperature of the air that flows through the heater coil and into the cab is controlled by the amount of coolant that circulates through the heater coil. The coolant transfers the heat into the air stream. By increasing the amount of coolant circulating the heater coil, the temperature of the air flowing out of the coil also increases. The coolant leaves the heater coil at a reduced temperature and flows back into the return valve for the engine cooling system.
The blower system controls how much air flow is passed through the evaporator and heater coil. The blower system is controlled manually through the HVAC operator controls. When the HVAC operator controls are in the all off position, the HVAC system is not engaged. Neither the air conditioning system nor the heating system nor the heating system will operate. When the HVAC operator controls put the blower in the LOW, MEDIUM, MEDIUM HIGH, or HIGH position, the HVAC system is activated. Depending on the position of the blower control, power is sent from the HVAC operator controls to the blower resistor pack. The resistor pack contains different resistors designed to adjust the power sent to the blower fan motor. The different power levels correspond to different fan speeds in the blower system. the blower fan motor pulls in air from the cab recirculation. This air comes from a return vent to the lower left operator seat. the fan pushes the air through the evaporator and heater coil. The air is then sent to the louvers.