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| Illustration 1 | g06572583 |
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Electrical schematic of the HVAC system. (1) Compressor (9) Implement ECM (10) HVAC operator controls (11) A/C Switch (12) Precleaner (13) Condenser Fans (15) Discharge pressure sensor (16) Louver temperature sensor (17) Blower fan motor (18) Suction pressure sensor (19) Evaporator temperature sensor (20) Water valve actuator (21) Recirculation temperature sensor (22) Ambient temperature sensor | |
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| Illustration 2 | g06572543 |
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HVAX cooling (2) Condenser (4) Evaporator (5) Accumulator (15) Discharge pressure sensor (18) Suction pressure sensor (19) Evaporator temperature sensor (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 | |
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| Illustration 3 | g06572551 |
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HVAX heating (2) Condenser (3) Expansion valve (4) Evaporator (5) Receiver dryer (6) Water Valve (7) Heater Coil (16) Louver temperature sensor (22) Ambient temperature sensor (E) Coolant from engine (F) Coolant to radiator | |
The HVAC system has two modes of operation: HEATING, and AIR CONDITIONING. The operator selects the mode of operation through the A/C Switch (11). In both modes, the operator has control of the blower fan and temperature setting. The operator can select OFF, MANUAL, or AUTO blower fan speed.
Note: The HVAC system will not operate if the blower fan control is in the OFF.
The air conditioning system is activated through operator request from the A/C switch (11) in air conditioning mode.
When the air conditioning system is activated, ECM (9) sends a signal to A/C clutch on compressor (1). Discharge pressure sensor (15) and suction pressure sensor (18) verify that the high and low-pressure sides of the A/C system are functioning correctly. If either of the two sensors detect pressures out of specifications, the ECM (9) receives a signal and shuts off the signal to A/C clutch on compressor (1). Evaporator temperature sensor (19) monitors the temperature of the evaporator (4). When the temperature of evaporator coil drops below a specific point, ECM (9) receives a signal and shuts off the signal to A/C clutch on compressor (1). Once the temperature of the evaporator coil raises back above the specific point, implement ECM (9) receives a signal and re-engages the signal to A/C clutch on compressor (1). The process of the air conditioning system turning on and off is called cycling.
When 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. 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 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. This transfer changes the refrigerant to a high temperature and high-pressure liquid.
From the condenser coil (2), the refrigerant moves through the receiver dryer (5) then to expansion valve (3). The expansion valve regulates flow to maintain vapor at the outlet of the evaporator and causes a pressure drop in refrigerant. The pressure drop causes the refrigerant to change from a high pressure and a high temperature liquid to a low pressure and a low temperature mixture of liquid and vapor.
The low pressure and low temperature refrigerant moves to the evaporator coil (4). While the refrigerant is in the evaporator coil, the refrigerant absorbs heat from the air flow. This absorption changes the refrigerant to a low pressure and low temperature vapor. Moisture is removed from the refrigerant by an internal desiccant.
From the evaporator coil (4), the refrigerant moves back to the compressor inlet.
The refrigerant returns to the compressor (1) as a low pressure and low temperature vapor. This action marks the end of the cycle. The cycle is repeated continuously.
The machine is equipped with condenser fan reversing function. This function allows the fan to reverse to remove any debris that has accumulated in the condenser fins.
The condenser fan runs at various speeds. The fan speed varies between low speed at 30% or condenser inlet pressures of
After 3 times of reversing, an event will be logged. The condenser needs cleaned and the AC will be disabled until the key is cycled.
When switched from A/C mode to "OFF" mode, the condenser fans are signaled to reverse.
The heater system operates using coolant from the engine (E). The hot coolant from the engine circulates through the heating system. This coolant from the engine (E) flows from the outlet valve for engine cooling system, through water valve (6), through heater coil (7), and flows to the radiator (F). The heating system is controlled by the temperature control knob, which is on the HVAC operator controls (10).
Temperature is controlled to a setpoint on the control panel and the coolant system is controlled by the ECM. With the temperature control knob in the maximum cold position, water valve (6) is closed. The CLOSED position prevents the flow of coolant into heater coil (7). When the control knob is moved away from the maximum cold position toward the maximum heating position, the heater control valve begins to open. As the control valve opens, high temperature coolant begins to flow through the water valve (6) and into the heater coil (7). 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 is flowing out of heater coil (7) 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 that is circulating through the heater coil, the temperature of the air that is flowing out of the coil also increases. The coolant leaves the heater coil at a reduced temperature and the medium temperature coolant flows to the radiator (F).
The blower system controls how much air flow is passed through the evaporator (4) and heater coil (7). The blower system is controlled manually through HVAC operator controls (10). Blower speed control knob is in the OFF position, the HVAC system is not engaged. Neither the air conditioning system or the heating system will operate. System is activated in any position other than OFF position. The system stays active all the time in "AUTO"mode. Blower fan motor (17) pulls in air from the cab recirculation and the fresh air filters. The fan pushes the air through evaporator (4) and heater coil (7). The air is then sent to the louvers and out to the cab of the machine.