Operation CHARM: Car repair manuals for everyone.

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 sliding the temperature control, located on the HVAC control module, to any setting. The temperature control can change the vehicle's air temperature regardless of the HVAC mode setting, heater or A/C.

The fuse block provides power to the left air temperature actuator through the ignition 3 voltage circuit. Power and ground are provided to the HVAC control module by the ignition 3 voltage and ground circuits.

When a desired temperature setting is selected, the HVAC control module outputs a voltage signal to the air temperature actuator over the control circuit of the air temperature actuator. A potentiometer inside the HVAC control module varies the voltage value on the control circuit based on the position of the air temperature switch. Based on the voltage value on the control circuit, the actuator positions the air temperature door to a to divert sufficient air around or through the heater core to achieve the desired vehicle temperature. Ground is provided by the ground circuit of the air temperature actuator.

Dual Zone
The HVAC control module has dual sliding temperature switches. The fuse block provides power to the right air temperature actuator through the ignition 3 voltage circuit.

When a desired temperature setting is selected, the HVAC control module outputs a voltage signal to the air temperature actuator over the control circuit of the air temperature actuator. A potentiometer inside the HVAC control module varies the voltage value on the control circuit based on the position of the air temperature switch. Based on the voltage value on the control circuit, the actuator positions the air temperature door to a to divert sufficient air around or through the heater core to achieve the desired vehicle temperature. Ground is provided by the ground circuit of the air temperature actuator.

The dual zone controls allows for maximum temperature offset between the driver and passenger. It is possible to divert maximum airflow around the heater core with one dual zone switch and divert maximum airflow through the heater core with the other dual zone switch. Each air temperature actuator is independent from the other and the passenger side is not limited in the range of temperature offset.

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 assembly. The heat of the coolant flowing through the heater core is absorbed by the ambient air drawn through the HVAC assembly. Heated air is distributed to the passenger compartment, through the HVAC assembly, for passenger comfort. The amount of heat delivered to the passenger compartment is controlled by opening or closing the HVAC assembly temperature door. The coolant exits the heater core through the return heater hose and recirculated back through the engine cooling system.