VW Passat blower motor resistor. The resistor for the blower motor is used to vary the fan speed. If your resistor goes your heater may only blow at one speed, if it does at all. Replace it with this original equipment quality blower motor resistor.
If your VW Passat blower motor resistor went bad, there is a good chance your blower motor is fried too. The direct fit replacement for the Jetta, Golf, and New Beetle is on this page. You will also want a guide to get you through the tight spaces in the dashboard to reach your blower motor resistor. There is no better guide than the Bentley manuals when you are working on any Volkswagen.