Heater and A/C Control Assembly

HVAC Control Assembly:

The heater and A/C control is the vehicle operator's control point for the manual air conditioning system. The heater and A/C control includes a rotary knob to select the system operating modes (OFF, MAX A/C, NORM A/C, BI-LEVEL, VENT, HEATER, DEFOG, DEFROST), a temperature control and fan speed rotary knob and a rear defogger switch.

MODE SELECTOR KNOB

The rotary mode selector knob on the HVAC control panel controls two electrical switches and a vacuum valve; the electrical switches activate the blower and the A/C compressor, the vacuum valve applies or vents vacuum to the vacuum actuators which determine air intake and discharge locations. By applying vacuum to these actuators in various combinations the vacuum valve controls whether air comes out the floor outlets, panel outlets or defroster outlets and whether fresh (outside) air is drawn into the system or inside air is recirculated.

TEMPERATURE CONTROL KNOB

The rotary temperature control knob is a potentiometer which sends a voltage signal to the A/C temperature valve actuator. The voltage signal varies according to temperature knob position.

When the temperature control knob is moved fully to the left (COOL), less than 1 volt is applied to the A/C temperature valve actuator.

When the knob is moved fully to the right (WARM), battery voltage is applied to the A/C temperature valve actuator.

FAN SPEED CONTROL KNOB

The fan speed control knob is used to actuate the fan speed switch inside the heater and A/C control Fan switch position determines whether current flows to the blower resistor assembly or to the blower relay. With the mode selector knob in any position but off, the fan circuit is activated and the fan operates at the speed selected.

TEMPERATURE VALVE ACTUATOR

The A/C temperature valve actuator controls outlet air temperature, following a voltage signal from the temperature knob in the heater and A/C control.

A reversible DC motor in the actuator operates the temperature valve, which determines how much air passes through the heater core.

When the temperature knob is in the COOL position (fully left), less than 1 volt is applied to the actuator and its motor runs to move the temperature door and block air flow through the heater core. No heating of system air occurs.

When the temperature knob is in the WARM position (fully right), battery voltage is applied to the actuator and the motor runs to move the temperature door and force all air to flow through the heater core. Maximum heating of system air occurs.

BLOWER RESISTOR ASSEMBLY

The blower resistor assembly is used in combination with the blower switch to determine blower speed. The blower resistor assembly consists of three resistors in the same housing: with the blower switch in LO, all three resistors are placed in the blower circuit and the blower motor runs at the lowest speed; with the blower switch in M1, two of the resistors are used and the blower motor runs faster; with the blower switch in M2, just one of the resistors is used and the blower motor runs even faster; with the blower switch in HI, none of the resistors are used and the blower motor runs at maximum speed.

BLOWER RELAY

The blower relay makes it possible to apply battery voltage directly to the blower motor without using heavy gauge blower circuit wiring or a high current capacity blower switch.

When the blower switch is in LO, M1 or M2, the blower relay is de-energized. Current flows through the blower resistor assembly and the de-energized relay contacts to the blower motor. The blower motor runs at LO, M1 or M2 speed - none of these speeds requires high current flow.

When the blower switch is in HI, current flows through the blower switch to the blower relay and energizes the relay coil. The relay contacts change position and current flows directly from the RH underhood fuse block to the blower motor, through the energized relay contacts.

HEATER AND A/C MODULE

The heater and A/C module is where all system air is heated, cooled, mixed together and directed to the various ducts and vents. The module consists of a housing with inlet openings, outlet openings, air passages and air valves. Vacuum actuators and an electric motor (mounted to the side of the case) operate the air valves according to the A/C solenoid switch assembly signals.