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What is the heating system/what does it do?

A car's heating system is responsible for providing fresh, warm or hot air to the interior cabin as required by the occupants. Using dash board controls the air can usually be directed to different locations of the interior including the windscreen and side windows, directly at the driver and passengers or into the foot wells and floor area (or variable combinations). The air temperature can be adjusted from ambient external (fresh air) to 50˚C+. Additionally most heating systems allow for the car's airflow to be recirculated and thus preventing external air from entering the cabin. Finally, the speed of the airflow can be controlled by a variable fan.

Getting into the details of the heating system

Some heating systems integrate with air-conditioning and or climate control systems allowing a constant internal temperature to be set. The combined system will then regulate the airflow and temperature as required to maintain this regardless of changes to external temperature, sunshine etc. These systems often include options for rapid defrosting and demisting of windows.

Airflow for the system enters the car through an inlet somewhere on the bonnet and this is ducted to the heater matrix, core or radiator. In water cooled engines the matrix is heated using hot water which is piped in from the engines cooling system. The airflow is passed through the matrix and is warmed as required.

The matrix temperature is controlled via a valve or regulator which is linked to the dashboard controls. This determines how much heat is allowed to flow from the engine to the matrix and therefore the level of heat that is added to the airflow.

The majority of the heating system is housed within the dashboard allowing the controls to be conveniently located in the centre console or central dash area. Some of these controls are mechanical and link directly to flaps, vents or valves varying the different elements of the system.

Heated air is ducted to the various locations around the vehicle with additional controls for air vents at the key areas including across the width of the dash and sometimes in the rear centre console and door pillars.

What if something goes wrong with the heating system?

Due to the large number of components within a car's heating system diagnosis of problems can prove challenging. However, there are some obvious signs that should lead towards the root cause of specific issues including (but not limited to):

  1. Water in the front foot wells of the car may suggest issues with the heater matrix or related pipework and hoses.
  2. Heater fan not functioning correctly could be linked to problems with the blower fan motor, including motor failure, fan damage, resistor pack wear or electrical or switch issues.
  3. Heater controls not working correctly would suggest possible failure of heater direction control switch, heater valve or air vent mechanism.
  4. Airflow not present at all correct locations could be linked to problems with damaged or disconnected ducting, heater direction control switch or other control elements.