Is Your Car Heater Ready for Winter

One morning you go out to your car and realize it’s time to swing the heater control from blue to red. Is your car heater ready for winter? Here we’ll discuss some common problems when your vehicle refuses to comply with the command to provide heat. We’ll also discuss some basic maintenance checks to make sure the hot keeps coming all winter long.

Heat I Command You

A few things happen when you swing the heater control knob from cold to hot. Everything must operate together as per design intent or lack of heat is the result. Inside the car a device known as the temperature door diverts air flow from the blower motor to be pushed across the heater core instead of the AC evaporator. This component is capable of blending the amount of air flowing across both heat exchanging devices to produce the desired output temperature.

In the case of dual zone climate control there is a separate blend door for the passenger side and the driver side. On older cars operation of this temperature blending door was controlled by a manually operated cable. On modern vehicles this is controlled by a computer module that actuates an electric motor. Improper calibration or malfunction of the electrical door motor can cause undesirable results. Often when this system malfunctions drivers hear an audible clicking sound inside the car when adjusting the temperature from the control panel.

Lack of Airflow

When air is restricted from flowing across the heater core, output temperatures can suffer. Most automobiles have the fresh air inlet that feeds the blower motor at the base of the passenger side windshield. This also happens to be a common area where leaves, twigs, acorns and other debris caused by the change of seasons will collect. Car owners should put on a pair of heavy gloves, raise the hood and clean out any debris from this area as the seasons change from fall to winter.

There are two more items to discuss when airflow issues are determined as the root cause of heater problems. Many vehicles come with cabin air filters that are often neglected by both repair shops and drivers. If you find debris near the fresh air inlet, there’s a good chance this has also worked its way down into the cabin air filter. Finally, blower motor problems are another source of airflow issues. The speed at which the blower motor spins is controlled by a blower resistor, relay and the circuit protected by a fuse. Malfunctions in any of these areas will cause low heater output.

You Need Hot Water

Another thing that takes place when you push the temperature control to the hot side is engine coolant will begin to flow through the heater core. This is facilitated through the heater control valve, usually located in the engine compartment near the firewall. These devices can be electrical or vacuum operated. Mechanics will perform a quick touch and feel test if they believe this part is malfunctioning.

When the engine is at operating temperature they’ll touch the hose leading up to the heater control valve. Then they feel the hose on the other side of the valve that heads towards the heater core. These two hoses should feel about the same temperature. Malfunction of the heater control valve that is stuck closed will be hot on one side and cool on the other. Automobiles with engine thermostat problems will have cold hoses on both sides of the valve.

Common Problems Causing Lack of Heat

There’s one thing most mechanics will check first on a lack of heat complaint. Low coolant level is often found when drivers complain of erratic heat operation. Small coolant leaks that went undetected all summer long can show their face when the first cold days of fall arrive. If coolant is dripping onto the hot engine it turns to steam and evaporates long before it hits the ground, leaving the driver unaware of any cooling system problems. As the coolant level drops, the heater core, which is considered an accessory, is one of the first devices to run dry. The priority of the cooling system is to circulate water through the engine block and radiator. This can provide a situation where the antifreeze is low, but the engine doesn’t overheat, yet there isn’t enough reserve water to flow continuously to the heater core.