Is your heater core warm/hot? If so...
the internal flaps which direct airflow over and or around the heater core, may have one of their electric motors gone bad...
One of my previous posts-
2004 A4 1.8t USP Quattro 6MT
K04-15/APR/TT 225 Injectors/Custom Stainless Exhaust/710N/RaceTec FMIC
034 HFC/Jet-Hot Cermi-coated & ported exhaust manifold
Spec Stage 3+ with OE DMFW!
Neuspeed TIP/Neuspeed Snub/Optima 75-35/AFE Pro-Dry/FSI Coils
AMS Short-shift @ %40 redux(Sweet!)
Bilstein Sport with H&R/ H-Sport Anti-Sway bars/E-codes
19x8.5 OEM Audi Skinny Fives with 235-35 Bridgestone 760 Sport Skins
B7 A4 brakes with StopTech Ceramic pads and Stop Tech rotors
Sirius Satellite Radio
Ross-Tech HEX-USB+CAN Equipped