Heater blows cold air


Driving a 2001 Audi A4 with 130K - The weather is starting to get cold here in Dallas. Noticed the heater is just blowing cold air no matter how high I turn the temperature. Is this a quick fix? And if so, can you provide some instructions?

The temp control switch may be at fault.

The blend door motor (that controls a door to direct cold air or hot air between the outside vents/A/C and the heater) may be faulty.