The main control module is responsible for processing output signals from the control panel. The processed signals control actuator motors that are located on the unit. These signals also control the fresh air vent and the speed of the blower motor.
When the system is in the "AUT" mode, the control module will monitor signals for the following sensors:
- Temperature sensor (Outlet air)
- Temperature sensor (Fresh air)
- Temperature sensor (Recirculating air)
- Temperature sensor (Evaporator)
- Sunlight sensor
The functions that follow are controlled automatically:
- Blower fan speed
- Air distribution
- Temperature of the Cab
Automatic Selection of the Air Outlets     | |
Outside Temperature     | Air distribution     |
? 22 °C (71.6 °F)     |
Panel     |
? 0 °C (32.0 °F) < 22 °C (71.6 °F)     |
Panel and Floor     |
< 0 °C (32.0 °F)     |
Floor     |
The operator enters a temperature setpoint on the control panel. The control module uses information that is retrieved from the sensors in order to control the temperature of the air. When the signal is received from the control panel, the control module will respond according to the command that is entered. The "AUT" mode controls the temperature in the cab.
Initialization
When the control module receives power, the operation mode is first determined. If the system is in the OFF mode, the control module will send the code for the OFF mode to the control panel. If the control module is in the ON mode, the control module will determine the mode of operation. The following modes will be selected by the control module:
- Heat only
- Air Conditioning
The operation mode is directly related to the sensor input.
Operation Modes for Air Flow
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Illustration 1 | g00892720 |
(1) Actuator (Air distribution) (2) Actuator (Door Assembly) (3) Actuator (Air intake) (4) HVAC controller |
OPERATION OF ACTUATOR MOTOR (1) (1)     |
||
---|---|---|
SELECTED MODE for AIR FLOW     | Air Door (2)     | ROTATION     |
Degrees from Center | ||
Panel     | Air door (Floor vent)     | 9°     |
Panel and Floor     | 60° | |
Floor     | 93° | |
Mixed     | 65° | |
Defrost     | 9° | |
Panel     | Air door (Rear vent)     | 109°     |
Panel and Floor     | 114° | |
Floor     | 155° | |
Mixed     | 180° | |
Defrost     | 139° | |
Panel     | Air door (Defroster vent and Front Vent)     | -13°     |
Panel and Floor     | -13° | |
Floor     | 21° | |
Mixed     | 55° | |
Defrost     | 55° | |
OPERATION OF ACTUATOR MOTOR (2) (1)     |
||
SELECTED MODE for AIR FLOW     | Air Door (2)     | ROTATION     |
Degrees from Center | ||
Maximum cooling     | Air door (Door Assembly)     | 0° Air flow through the heater core is blocked.     |
Max heat     | 117° Air flow through the heater core is not blocked. |
|
OPERATION OF ACTUATOR MOTOR (3) (1)     |
||
SELECTED MODE for AIR FLOW     | Air Door (2)     | ROTATION     |
Degrees from Center | ||
Fresh air     | Air door (Fresh air and Recirculating air)     | 90° Fully opened     |
Recirculating air     | 0° Fully closed |
( 1 ) | Refer to illustration 1 in order to properly identify actuator motors. |
( 2 ) | Refer to the System Operations, "Air Conditioning System" section in order to properly identify the air doors. |
Note: Actuator motor (2) is part of the air door (Door Assembly). This motor is actuated when the operator changes the setpoint by pushing INCREASE or DECREASE on the temperature selection switch. Refer to "Initialization" for further information.
Note: Actuator motors (1), (2) and (3) function similarly. Refer to Systems Operation, "Actuator Motor (Damper Assembly)" for schematic information.
Operation of the Automatic Temperature Control mode (ATC)
![]() | Automatic temperature control switch |
If the heater/air conditioner is in the ON position, the code for automatic temperature control "AUT" causes the control module to enter the automatic mode of operation. In order to maintain the temperature of the cab at the setpoint, the control module performs the following steps:
- Obtain the temperature setpoint of the cab that is located in non-volatile memory.
- Adjust the speed of the blower fan.
- Control the position of the air door (Door Assembly).
- The control module controls the selection of the air outlets.
- The control module controls the solenoid for the air conditioner.
Operation of the Maximum Cooling Mode
Rotate the temperature control counterclockwise for Maximum cooling mode. The set point of the control is set at 15.5 °C (59.9 °F).
When the system is in the maximum cooling mode, the control module will monitor signals for the following sensors:
- Cycle the compressor clutch.
- Operate the blower fan at the highest speed.
- Temperature sensor (Outlet air)
- Temperature sensor (Evaporator)
- Sunlight sensor
The functions that follow are controlled automatically:
- Blower fan speed
- Air distribution
- Temperature of the Cab
Operation of the Maximum Heating Mode
When the system is in the "AUT" mode, the control module will monitor signals for the following sensors:
- Temperature sensor (Outlet air)
- Temperature sensor (Recirculating air)
- Temperature sensor (Fresh air)
- Temperature sensor (Evaporator)
- Sunlight sensor
The functions that follow are controlled automatically:
- Blower fan speed
- Air distribution
- Temperature of the Cab
Operation of the Manual Heat Mode
Depress the temperature control knob while the unit is in automatic mode. This will place the unit in manual heat. When the controller receives the code for manual heat, the controller moves the air door (Door Assembly) to a fixed position. Sixteen positions are available. The blower fan speed will not change. The speed can be changed by rotating the fan control knob. Rotating the temperature control knob will move the air door (Door Assembly).