2003 SAAB 9-3 repair Question car heaters

DON WEST

MEMBER
2003 SAAB 9-3

2003 Saab 9-3 repair Question

My question is not specific to my car but about car heaters in general.I am in a heated debate with a buddy. My buddy says that if you set the temperature controls on the dash of your car to a higher temperature the actual temperature of the air coming from the vents will be hotter.I contend that the temperature of the air will be the same at a lower setting, but will just cut off sooner. It is my assumption that the temperature is a function of the temperature of the coolant in the coils of core and that the thermostat opens and closes the coolant flow in the coils. We both understand that turning the fan up will force more warm air into the cab. Can you help us before we come to blows?

1 Reply

DAVE H

MECHANIC
13,383 POSTS

The temperature in the heater core is always the same. Full heat settng into cab allows full heat flow from core. Turn heat setting down and the hot air is mixed with cool air from outside the vehicle to allow the correct temp flow into cab. So the actual flow from the vents is not always the same temperature

The control of the mixed-air temperature is achieved via a control wire connected to the air-mixing dampers. Cars equipped with ACC have a stepping motor that controls the air-mixing dampers.
The air temperature from the heater box is affected by the fan speed as well as the position of the air-mixing dampers. For certain markets, the coolant flow through the heater box can be completely closed off through a vacuum-operated coolant shut-off valve in order to achieve maximum cooling effect (applies to cars with A/C). This solenoid valve is activated when the climate control system is to provide maximum cold.
Depending on the desired heat/temperature position, the air-mixing dampers direct a certain amount of the incoming air through the heater box.
If the "cold air" position has been selected, the air-mixing dampers are closed and the air is prevented from reaching the heater box.