The heater on my ford focus makes a wailing sound when running and only works on full power. When it's wailing the airflow to the car is really restricted, but sometimes it works fine - when it works properly you could turn it off then on again and it will start wailing again and the airflow is rubbish.

Any ideas?

The wailing sounds like it's coming from behind the glovebox on the left somewhere.

Alison, January 2009

The heater fan will be either choked with leaves or the bearing will be gone. It will only be working on full power because the thermostat is faulty. This is normally found in one of the heater ducts close to the heater motor.

Craig, January 2009