312B, 320B, 322B, 325B, 330B and 345B Excavators Air Conditioning and Heating Systems with R-134a Refrigerant Caterpillar


Control Module - Main Control Module - Heater/Air Conditioner Unit

Usage:

320B 1XS
The main control module is responsible for processing output signals from the control panel. These signals in turn control upper and lower actuators that are located on the HVAC unit, as well as controlling 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:

  • cab temperature

  • outside (ambient) temperature

  • coolant temperature

  • evaporator temperature

  • sun load

Based on a set point entered on the control panel, the control module uses the above information in order to control the water valve and the a/c system. Upon receipt of command codes from the control panel, the control module will respond according to the command entered. Control of the cab temperature while in the "AUT" mode depends on proper function of the control module.

Initialization

When the control module receives power, it shall first determine if it is in the OFF mode. If it is in the OFF mode, the controller will send the code for the OFF mode to the control panel. If the control module is in the ON mode, the controller shall determine the mode of operation (HVAC or Heat Only) based on the state of the sensor inputs.

In the automatic fan mode, the fan speed will be low speed until initialization of the water valve takes place. After the sensor readings stabilize, the fan speed will then change to the control point speed. In the manual fan mode, the fan speed will be low speed until initialization of the water valve takes place and then change to the retrieved set point.

Operation of Air Flow Modes




Illustration 1g00396219

(1) Actuator for upper body

(2) Actuator for under seat

(3) Actuator for fresh air return

(4) Actuator for water valve

Table 1
OPERATION OF MOTOR ACTUATORS    
SELECTED AIR FLOW MODE     POWERED ACTUATOR (2)     ROTATION    
DIRECTION DURATION (seconds)    
Upper Body     1     Counterclockwise     10.7    
2 Counterclockwise     10.7    
Under Seat     2     Clockwise     10.7    
1 Clockwise     10.7    
Upper Body and Under Seat     1     Counterclockwise     10.7    
2 Clockwise     10.7    
Defrost     (1)     Clockwise     10.7    
1 Counterclockwise     2.8    
2 Counterclockwise     10.7    
Fresh Air     3     Clockwise     10.7    
Recirculate     3     Counterclockwise     10.7    
( 2 ) Refer to illustration 1 for proper identification of actuators.
( 1 ) Actuator (1) moves in both directions in order to achieve the correct position for the Defrost mode.

Note: Actuator (4) is part of the water valve assembly. This motor is actuated when the operator changes the set point by pushing INCREASE or DECREASE on the temperature selection switch. Refer to "Initialization" for further information.

Note: Actuators (1), (2) and (3) are all the same. Refer to Systems Operation, "Motor (Air Conditioner Control)" for schematic information.

Operation of the Automatic Temperature Control Mode (ATC)


Automatic temperature control switch

While in the HVAC application, the receipt of the "AUT" temperature code causes the controller to enter the automatic mode of operation. In order to maintain cab temperature to the control point, the controller does the following:

  • It retrieves the cab temperature set point from non-volatile memory.

  • It takes control of the fan speed.

  • It takes control of the water valve.

  • It takes control of the A/C solenoid.

Receipt of a second "AUT" temperature code puts the controller in the fan only mode and initiates the following:

  • The water valve will close.

  • The A/C output will turn off.

  • The fan speed will remain at the present level set by the automatic mode

While in the Heat Only application, the receipt of the "AUT" temperature code causes the controller to enter the automatic mode of operation. In order to maintain cab temperature to the control point, the controller does the following:

  • It retrieves the cab temperature set point from non-volatile memory.

  • It takes control of the fan speed.

  • It takes control of the water valve.

Receipt of a second "AUT" temperature code puts the controller in the fan only mode and initiates the following:

  • The water valve will close.

  • The fan speed will remain at the present level set by the automatic mode

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