I'd bet 100% that it's your electronic blend door actuator. Mine failed a few weeks ago. Try using your AC...and then start turning the temp to "hot" and see if the AC gets warmer - My AC would stay locked in on the coldest temp when the actuator failed. I tested mine by removing the old actuator, with wiring still plugged in, and moved the temp **** on the dash, but the actuator never moved. Plugged wiring into a known good actuator to confirm failure of part - I replaced with a blend door acuator from NAPA. BTW, the back screw is a pain to remove/install.
'08 Vista Blue XLT 2.3 DOHC
'11 Suzuki S40 - SOLD (5-3-2012) - Newest '12 Yamaha XT250