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, a variable resistor is used to determine the air temperature door control signals value. A resistor inside the HVAC control module provides a varying ground. This changes the 12-volt signal coming into the actuator and varies the voltage so the actuator is moved into the proper position. The motor opens the left air temperature actuator to a position to divert sufficient air past the heater core to achieve the desired vehicle temperature. Ground is provided by the ground circuit and HVAC control module.

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 offset temperature setting is selected, a variable resistor is used to determine the right air temperature door control signals value. A resistor inside the HVAC control module provides a varying ground. This changes the 12-volt signal coming into the actuator and varies the voltage so the actuator is moved into the proper position. The motor opens the right air temperature actuator to a position to divert sufficient air past the heater core or evaporator to achieve the desired vehicle temperature. Ground is provided by the ground circuit and HVAC control module.

The dual zone controls allows for maximum temperature offset between the driver and passenger. It is possible to select maximum airflow over the evaporator core with one dual zone switch along with maximum airflow over 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.