K Tahoe 4WD V8-4.8L VIN V (2000)
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Manual operation
In the manual operation mode 13 speed settings are available and, once selected, the fan speed remains constant until a new speed is selected. In the
automatic operation mode the ECC module will determine what blower speed is necessary in order to maintain customer selected temperature.
HVAC Compressor Controls Circuit Description
The HVAC air delivery electrical system consists of a control module, blower switch, mode and temperature potentiometers & (motors), recirculating
outside air control push button, temperature, mode and recirculating motors that operate their respective actuators and doors.
The mode, recirculating and temperature door motors are powered by ignition 3 voltage when the ignition switch is in the RUN position. The ground
path is provided by the body wiring harness junction block to ground located in the left hand upper plenum area. The HVAC control module is powered
by ignition 3 voltage from the HVAC fuse located in the fuse block when the ignition switch is in the RUN position. Grounding for the module is
through the same circuit utilized for the door motors.
The recirculating door motor is controlled by a signal from the HVAC control module via recirculation actuator control when the push button is activated
on the control head. Also, the recirculation door motor can be controlled by the PCM which monitors the automatic recirculation switch activity (located
at the bottom right hand side of the Air Conditioning (A/C) condenser) and will signal the door motor to the recirculating mode when the switch closes
due to high refrigerant pressure. This will allow cooler air from inside the vehicle to flow over the A/C evaporator thus cooling the refrigerant
temperature.
The mode and temperature door motors are positioned in proportion to the variable voltage signal received from the HVAC control module. Adjusting
the temperature dial (potentiometer) in the control head provided a variable (0-5 volts) voltage to the door motor via temp actuator control. There is a
constant 5 volt reference sent to both motors via 5 volt reference from the control module. The module uses this reference voltage to accurately
determine the door motor position through a feed back temp actuator signal which also varies from 0-5 Volts.
The air delivery mode functions consist of vent, bi-level, heater, defog and defrost (non rear HVAC vehicles) and upper or lower (Rear HVAC vehicles).
The mode door motor operates in the same manner as the temperature door except for the signal and feed back circuits which are mode actuator control
and mode actuator signal respectively. The HVAC control module receives a mode signal from the control head and will adjust the voltage control signal
to the motor in accordance with the mode selected.
