Winter Troubleshooting Tips for Vehicle Heating, Ventilation and Air Con

On these cold winter days it’s important for driver road safety and comfort to avoid any issues the vehicle Heating, Ventilation and Air Conditioning (HVAC) systems. Here we provide essential information and troubleshooting tips from specialists to avoid any blowouts this winter.

On top of driver comfort, interior blowers and heater resistors work in tandem with the rest of the Heating, Ventilation and Air Conditioning (HVAC) system to assist driver safety. They regulate temperatures to keep the driver alert and prevent windscreen fogging. Due to their frequency of use, interior blowers and heater resistors are often high-demand components. As they are interlinked, many technicians tend to misdiagnose problems with these parts.

FPS suppliers of HVAC components – Nissens, Valeo, Hella, febi, Denso and Bosch, have come together to clear the air about these components.

Interior Blowers

Located in the HVAC module between the cabin air filter and the evaporator or heater radiator, interior blowers function to continually draw air from the outside or maintain air re-circulation inside the passenger cabin. It takes cold air from the evaporator or warm air from the heater radiator.

Interior blowers are made up of an electrical motor and many plastic parts. Due to the temperature variances, it is important that the plastic elements are constructed using good quality materials for durability.

Carbon brushes and copper wirings within the electrical motor must be able to withstand electrical peaks during normal working conditions. High electrical loads can cause low-quality carbon brushes to melt and warp the plastic covers, leading to interior blower failure.


Problem: Blower does not start regardless of speed selected.

Try: Checking if the fuse is blown and if so, replace it with a new one that is the same voltage. Alternatively, check if the connector to the blower is mounted correctly and make sure that the blower wheel is clean, without obstruction. Also, check if the generator is producing more voltage than appropriate for the blower.

Problem: Blower only starts in one or some of the selected speeds.

Try: Checking if the heater resistors are defective. In the event that the heater resistor is integrated into the blower, the entire unit must be replaced.

Problem: Blower is very loud and sometimes squeaky or blower runs slowly or at an inconsistent speed.

Try: Replacing the interior blower entirely. There is a mechanical defect with the carbon brush elements.

Heater Resistors

Heater resistors enable the heater blower motor to change the speed of the fan. While it works in tandem with the interior blower, it is often overlooked during inspection when a vehicle owner encounters a HVAC problem.

Without a resistor, the speed of the airflow from the blower motor cannot be changed or will completely fail to work. A faulty resistor can lead to an electrical drain, causing a flat battery as the fan will only work at the highest setting.


When a blower only operates out of two speeds instead of four, or when the blower completely ceases to function (i.e. no air from vents), there could be something wrong with the heater resistor. Faulty heater resistors need to be replaced swiftly to avoid further damage to the rest of the HVAC system following a thorough inspection.

FPS has one of the largest interior blower and heater resistor ranges available same/next-day within the independent aftermarket. Contact your local FPS representative for more information.

De-mist Windows Quickly

As winter draws in and temperatures fall, internal misting on vehicle windows becomes a common problem for drivers. Follow these tips to clear window mist quickly.

  1. Turn the vehicle heater up. Warm air absorbs more water than cold, by turning the heater on moisture will be drawn away from the windows.
  2. Turn the air-con on (if available). The air conditioning system dries out air as it circulates through the system. Alternatively some vehicles have a climate control system which will do the job.
  3. Turn off air re-circulation. Air inside the vehicle will tend to hold a lot of moisture. Draw in outside air which will be drier and help to defog the windows.
  4. Use a dehumidifier bag. Placing a dehumidifier bag under the windscreen can help to draw and capture moisture from the vehicle and away from the window.


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