C 3500 Truck 2WD V8-6.0L VIN U (2001)
A 5-volt reference signal is sent out over the 5-volt reference circuit to the mode actuator. When a desired mode setting is selected, a variable resistor is
used to determine the mode door position signals value. That varied 5-volt reference signal is sent back to the HVAC module software inside the HVAC
control module on the mode door position signal circuit. The HVAC module uses this reference voltage to determine the mode actuator position through
the mode door position signal circuit. The motor moves the mode door to the desired position. Ground for the mode actuator is provided by the ground
circuits and the IP wiring harness junction block.
Recirculation Mode
When the recirculation (REC) switch is pressed, a signal is sent from the HVAC control module to the recirculation actuator through the recirculation
door motor control circuit. When the amplifier circuit receives the signal, the recirculation actuator moves into the recirculation mode. This brings air
from inside the vehicle instead of fresh air from the outside. Power and ground are provided to the recirculation actuator by the ignition 3 voltage circuit
and the ground circuits through the left instrument panel junction block and splice pack. Recirculation is only available when the HVAC control module
is either in Vent or Bi-Level mode only. Vent and Bi-Level are the first 8 of 17 detents on the mode switch. An A/C request is made anytime the
recirculation button is selected. The recirculation mode will stay on and the LED will illuminate until either outside air or a non-recirculation mode is
selected or the next key-on ignition cycle. Recirculation is can be selected with the blower motor in either the ON or OFF position.
The recirculation door will move automatically with an input from the A/C high pressure recirculation switch. The PCM will place the A/C system in
recirculation mode when a signal is sent over the A/C refrigerant high pressure cut-out switch signal circuit. This allows for the cooler inside air to flow
over the A/C evaporator and cool the refrigerant temperature, until the high side pressure returns to normal.
Heater Option Only
On non-A/C equipped vehicles, the air distribution is selected by turning the mode switch. Moving the mode switch mechanically moves the mode door.
A mode cable connects the mode switch to the mode door. The mode door position determines the air flow to the desired air outlet. With the manually
operated heating and ventilation module, the operator can select either the defrost, vent or heat modes.
Air Distribution-Auxiliary Control
When the mode knob is turned, a signal is sent from either the front auxiliary HVAC control assembly on the auxiliary front mode signal circuit or the
rear auxiliary HVAC control assembly on the auxiliary rear mode signal circuit. These signals are received by the rear auxiliary HVAC control processor
and sent to the auxiliary mode actuator through the auxiliary mode door control circuit. When the control logic receives the signal, the auxiliary mode
door moves into the desired position.
The left instrument panel fuse block provides power to the auxiliary mode actuator through the ignition 3 voltage circuit, IP wiring harness junction
block and the auxiliary blower motor resistor assembly. Ground is provided by the ground circuits and a splice pack.
A 5-volt reference signal is sent out over the auxiliary mode door control circuit to the auxiliary mode actuator. When a desired mode setting is selected,
a 5-volt reference signal is sent from the rear auxiliary HVAC control processor to the auxiliary mode actuator. The motor moves the auxiliary mode
actuator to the desired position. Ground for the auxiliary mode actuator is provided by the ground circuits and a splice pack.
