Electronic Control Module (ECM)
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| Illustration 1 | g03579878 |
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(1) Connector view from ECM side
(2) Connector view from harness side | |
The ECM makes decisions based on input information and memory information. After the Implement ECM receives the input information, the ECM sends a corresponding response to the outputs. The inputs and outputs of the Implement ECM are connected to the machine harness by two 70 contact connectors (J1 and J2). The inputs and outputs to the ECM can be viewed through the Caterpillar Electronic Technician (Cat ET).
Note: Only the complete ECM is serviced (no lower levels components). The ECM must be replaced if the ECM is damaged. Replace the ECM if a failure is diagnosed.
The inputs describe the status of the machine systems. Two types of inputs exist. The inputs can be either a Switch type or a sensor type. Switches provide an open, a ground, or a + battery signal to the inputs of the controller. Sensors (frequency, PWM, or voltage) provide a changing signal to the sensor inputs of the controller. The inputs to ECMs are listed in table .
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| Illustration 2 | g03399469 |
Cab Air and Cab Ventilation Duct Air Temperature Sensors
Cab Air and Cab Ventilation Duct Air Temperature Sensors are PWM inputs to the Implement ECM. These two sensors are used to determine average cab air temperature.
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| Illustration 3 | g03399472 |
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(A) A/C mode
(B) Off mode (C) Automatic temperature control mode (D) Temperature dial (E) Blower speed dial | |
HVAC Blower Speed Control Position
The fan control position, controls the speed of the HVAC blower motor. Full counter clockwise position is the off position and the full clockwise position is the maximum fan speed. The dial is a potentiometer that provides an infinite variable blower speed option allowing the operator to choose the correct airflow quantity.
Note: Do not turn the blower speed dial to the full counter clockwise position unless you want to shut off the HVAC system.
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| Illustration 4 | g03399567 |
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High-pressure switch | |
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| Illustration 5 | g03399568 |
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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
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| Illustration 6 | g03399572 |
The 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
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| Illustration 7 | g03399574 |
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| Illustration 8 | g03399576 |
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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.
HVAC Water Valve Continuous Signal (Electronic Rotational Actuator)
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| Illustration 9 | g03399579 |
Electronic rotational actuator is used to control the flow of heat inside of the HVAC unit. The actuator controls the temperature of the airflow by opening and closing a water valve or a blend door type.
HVAC Blower Control Signal (HVAC Blower Driver Module)
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| Illustration 10 | g03399580 |
Blower driver module is used to control the blower speed on an HVAC blower motor. The driver controls the blower speed by varying the current going to blower motor. The controller will vary the current from 99% down to 35% of full rated speed.