On both my Renault Master van and my wives C4 the heater fan switch will only operate on full speed, with no in between speeds. Being only familiar with classic cars where a brush run over a copper coil I imagine its no longer made like that. Do I need to replace just the switch or is there another component that will need to be replaced. Cheers Barry

Hi, modern heaters have a electrical rheostat hidden away somewhere to control fan speeds try to find a manual online or just input Renault heater blower fault.

Resistor pack faulty or possibly the multiplug burnt out, don't know if a repair kit is available for the Renault but is probably available for the Citroen as it's likely to be the same as some of the Peugeot models. Check out the bay of e

Cheers guys

I bought a resistor thingy for a focus once only to find out it was the switch at fault. So might be worth a quick check.

Modern cars generally either still use a resisstor pack or on higher end and more recent designs a solid state module that controls the duty cycle of the motor supply.

Both types are generally mounted on the outside of heater unit with a heat sink "hedge hog" protruding through the casing exposed to the airflow.