BASE 9M8775 - Caterpillar

HVAC Auto Climate Control Switch and HVAC ON Switch
Illustration 4 g03399513The A/C selector switch is used to determine the operating mode for the HVAC system. The rocker switch has three positions. Bottom position, (C) in previous figure, sets the HVAC system into automatic temperature control mode. ECM located on machine controls A/C compressor clutch, water valve position, and desired blower speed automatically. Optional blower speed override is still available to the operator by using dial (A). Center position, (D) in previous figure, sets the A/C system into off mode but still allows operator manual control of the water valve and blower speed through dials (A) and ( B). Top position, (E) in previous figure, sets the HVAC system into manual A/C mode. The A/C compressor is permanently turned on and the operator has manual control of the water valve and blower speed through dials ( A ) and (B).High/Low Pressure Switch
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High-pressure switch
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Low-pressure switch
High/Low pressure switch, used to prevent unwanted high pressure and low-pressure conditions on the outlet of the A/C compressor. Low-pressure switch, used to prevent unwanted low-pressure conditions on the inlet side of the A/C compressor. Both the high/low and low-pressure sensors prevent operation of the A/C compressor during conditions of overcharge of the refrigerant and undercharge of the refrigerant.HVAC Evaporator Thermostat Switch
Illustration 7 g03399572The HVAC evaporator thermostat switch is a passive analog signal to the Implement ECM. This sensor is used to measure the temperature of the evaporator coil. The sensors operating range is MAX 120° C (248° F), MIN −40° C (−40° F).Outputs
Clutches
HVAC A/C Clutch
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(3) Magnetic clutch and pulley assembly
(4) Coil assembly
(5) Drive plate
(6) Bearing
(7) Compressor shaft The Implement ECM energizes the air conditioning clutch when the operator requests air conditioning and all of the conditions have been met.The compressor is driven by the engine. A belt connects the engine to the clutch and pulley assembly (3). The pulley assembly is located on the clutch. The drive plate (5) is fastened to the shaft of the compressor. The clutch and pulley assembly (3) turns on the bearing (6). The clutch and pulley assembly (3) are not connected to the shaft (7). The electric current from the thermostat controls a magnetic field in the coil assembly (4).The magnetic field pulls the drive plate (5) against the clutch and pulley assembly (3). The clutch and the pulley assembly (3) turns the shaft (7) that operates the compressor. When the current to the coil assembly (4) is stopped, the magnetic field is removed. This action allows the drive plate (5) to move away from the clutch and pulley assembly (3). The clutch and the pulley assembly (3) will turn freely on the bearing (6). The sequence of connecting and disconnecting the pulley to the compressor shaft (7) is called compressor cycling. The compressor cycling is controlled by the thermostat . The thermostat is controlled by the capillary tube, which is installed between the fins of the evaporator coil.Actuators
HVAC Water Valve Continuous Signal (Electronic Rotational Actuator)
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