HVAC Air Delivery Circuit Description

The HVAC air delivery electrical system consists the following components:
- A control module
- A six position blower switch
- A mode and temperature potentiometers
- Recirculating the outside air control push buttons
- Temperature, mode and recirculating motors that operate the appropriate actuators and doors

The mode, recirculating and temperature door motors are powered by CKT 341 (BRN) when the ignition switch is in the RUN position. The ground path is provided by CKT 2450 (BLK) via the Mid Bussed Electrical Center (MBEC) to G203 located in the left hand upper plenum area. The HVAC control module is powered by CKT 341 (BRN) from the HVAC fuse located in the Left Bussed Electrical Center (LBEC) 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 CKT 1614 (DK GRN) when the push button is activated on the control head. Also, the door motor can be controlled by the PCM/VCM which monitors the automatic recirculation switch activity. The automatic recirculation switch is located at the bottom right hand side of the A/C condenser. The switch 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 to 5 volts) voltage to the door motor via CKT 1199 (DK BLU). There is a constant 5 volt reference sent to both motors via CKT 598 (GRY) from the control module. The module uses this reference voltage to accurately determine the door motor position through a feed back CKT 733 (LT BLU) which also varies from 0 to 5 volts. The air delivery mode functions consist of Vent, Bi-Level, Heater, Defog and Defrost, The mode door motor operates in the same manner as the temperature door except for the signal and feed back circuits which are CKT 119 (WHT) and CKT 708 (RED) 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.