Heater Mode

The purpose of the heater is to supply heat to the interior of the vehicle. The vehicle operator can determine the level of heat by turning the temperature control, located on the HVAC control assembly, to any setting. The temperature control can change the vehicle's air temperature regardless of the HVAC mode setting, heater or A/C.

The instrument panel fuse block provides power to the air temperature actuator through the ignition 3 voltage circuit. Power and ground are provided to the HVAC control assembly by the ignition 3 voltage, ground circuits and splice pack.

When a desired temperature setting is selected, a variable resistor is used to determine the air temperature actuators setting. The resistor is located within the HVAC control assembly. Turning the temperature switch will vary the 12-volt signal. That varied 12-volt signal is sent to the servo amplifier inside the air temperature actuator on the air temperature door position signal circuit. The motor opens the air temperature door to a position to divert sufficient air past the heater core to achieve the desired vehicle temperature. The air temperature actuator is grounded through the ground circuit and splice pack.

When servicing an actuator, replace parts with the correct service parts for the actuator being serviced. The electric actuators for the manual HVAC system (C42 and C60) have a red R on top of them. This is to differentiate from the electric actuators used on the automatic HVAC system (C68).

Engine Coolant
Engine coolant is the key element of the heating system. The normal engine operating coolant temperature is controlled by the thermostat. The thermostat also creates a restriction for the cooling system that promotes a positive coolant flow and helps prevent cavitation.

Coolant enters the heater core through the inlet heater hose, in a pressurized state. The heater core is located inside the HVAC module. The heat of the coolant flowing through the heater core is absorbed by the ambient air drawn through the HVAC module. Heated air is distributed to the passenger compartment, through the HVAC module, for passenger comfort. The amount of heat delivered to the passenger compartment is controlled by opening or closing the HVAC module temperature door. The coolant exits the heater core through the return heater hose and recirculated back through the engine cooling system.

For a description of the RPO Code(s) shown in this article/images refer to the RPO Code List found at Vehicle/Application ID RPO Codes