Express 1/2 Ton Van V8-305 5.0L VIN M SFI (1998)
Control Module HVAC: Description and Operation
Heating System
Primary Heating System
The blower switch provides a choice of four blower speeds "Lo," "Med 1," "Med 2" and "Hi." The blower switch receives power from the HTR and A/C
fuse when the ignition switch is in the "ON" position.
In the "Lo" speed position, the circuit continues through the heater wiring harness to three resistors in the blower motor resistor relay.
In the "Med 1" speed position, the circuit continues through the heater wiring harness to the blower motor resistor relay, but it bypasses one of the three
resistors.
In the "Med 2" speed position, the circuit continues through the heater wiring harness to the blower motor resistor relay, but it bypasses two of the three
resistors.
In the "HIGH" speed position, the circuit continues through the heater wiring harness to the blower motor resistor relay, but it bypasses all three resistors
and closes the relay's normally open contact to provide full power to the blower motor from the HVAC maxifuse(R).
From the blower motor resistor relay, the circuit goes to the blower motor terminal. The blower motor circuit is completed to ground by a wire in the
heater wiring harness that goes from the blower motor terminal to the generator or A/C compressor bracket.
Auxiliary Heating System
The three-speed blower switch "Lo," "Med" and "HI" is located in the instrument panel, above the radio. In addition to controlling blower motor speed,
the switch also triggers an electro-mechanical valve to control coolant flow to the auxiliary heater core.
In the "Lo" speed position, the circuit continues through the heater wiring harness to two resistors in the blower motor resistor relay.
In the "Med" speed position, the circuit continues through the heater wiring harness to one resistor in the blower motor resistor relay.
In the "HIGH" speed position, the circuit continues through the heater wiring harness to the blower motor resistor relay, and closes the relay's normally
open contact to provide full power to the blower motor from the HVAC maxifuse(R).
