HOUSING 1S0320 - Caterpillar

Illustration 5 g03350808The evaporator freeze probe sensor is a passive analog sensor located on the evaporator. The sensor creates a different resistance depending on the surrounding temperature. The variations in resistance cause a proportional variation in voltage. This voltage is measured at the ECM contact, and allows the ECM to determine the evaporator temperature.Operator Temperature Control
Illustration 6 g03326001The operator temperature control sensor monitors the signal from the temperature control knob on the HVAC panel. This knob sets the operators desired temperature in automatic mode and adjusts the water valve in manual mode. In either mode, the ECM receives a pulse width modulated signal from the knob and HVAC panel that corresponds to a desired temperature or water valve position. The duty cycle is proportional to the position of the knob.Switches
Switches provide an open signal, a ground signal, or a +battery signal to the inputs of the ECM. Switches are open or closed.
When a switch is open, no signal is provided to the corresponding input of the ECM. This “no signal” condition is also called “floating”.
When a switch is closed, a ground signal or a +battery signal is provided to the corresponding input of the ECM.Air Conditioning Mode Switch
Illustration 7 g03325737The air conditioning mode switch is a two pole switch. The switch has two positions that control the operation of the air conditioning. In the automatic position the ECM controls the operation of the air conditioning to maintain a specified cab temperature. In the manual position, the air conditioning is manually engaged. The ECM has two contacts that pertain to this switch, one signals the ECM the switch is automatic mode, the other signals the ECM the switch is in manual mode. These contacts will float to a high voltage state unless the switch is closed to that contact. When the switch closes to a contact, the contact is pulled to a low or ground voltage state.Air Conditioning Low Pressure Switches
Illustration 8 g03350773
(1) High-pressure side low-pressure switch
(2) Low-pressure side low-pressure switch
(A) To ECM contact The air conditioning low-pressure contact at the ECM monitors the voltage state of the high and low pressure cutoff switches for the air conditioning. The switches are set up in series from a power source. The switches close and allow power to pass when the pressure in the high pressure and low pressures air conditioning loops is high exceeds the actuation pressure for the switch. If both switches have been actuated, both switches are closed and the ECM contact is pulled to a low or ground voltage state. If either switch has not been actuated, the ECM contact is pulled to a high voltage state.Outputs
The ECM responds to decisions by sending electrical signals to the outputs. The outputs can create an action or the outputs can provide information to the operator or the service technician.Relays
Condenser Fan Relays
Illustration 9 g03352416The condenser fan relays control the operation of the condenser fans. The relay is activated by the ECM when the air conditioning system is active. When the relay is activated, the relay