My truck is a 1993 and the heater control unit has been acting crazy here lately. It will only blow air out of the front of the dash, not the defrost or floor at all. I will blow at any speed, whichever i choose. If I select the dash setting or any combination between dash and floor it will sit there a couple of seconds and look fine (air won't change at all) and then the 5 little arrow things on the left will start blinking on and off. Any setting besides full defrost will cause the little arrows on the left to blink until i hit the defrost setting. Its kinda hard to defrost your windshield when your stuck on air in the face only. Anyone know what might be going on? Thanks for any help.

UPDATE: Seems the other night when I got in it to go somewhere it was still acting up. But when I got back in it to come back home it started working fine and has ever since. Possibly it was a stuck flap in the vents somewhere and a door shut or some kind of jar freed it. If anyone has anything they would like to add please do so.