Or maybe a 4/20 build date ? Sorry, I'm no help. Actually, maybe pull the resistor from the HVAC box, I believe it is accessible with it in the car. It may be cracked and could cause this now that I think about it.
Jason
Not aware that there are any common issues with these, other than occasionally people will have them out, and the auto / manual switch on the back will get flipped. Might want to verify that, as that will give you partial functionality if you have manual HVAC and it gets set for auto. Big...