Thought Mode Door 1 was broken, but now it works. Why?

[Crunch]

Late this winter I thought Mode Door 1 was broken on the HVAC system because air would only come out the dash vents. The temperature would change and the recirc door worked. But over the last few weeks I've noticed that Mode Door 1 seems to be working just fine again. I originally noticed that it didn't work all the time during the winter, and figured it was in the process of breaking. After it quit for several weeks I figured it was broken. Now it works again. What could cause this? I would have bet money that it was a mechanical problem, but now am wondering if it is an electronic or computer problem. Any thoughts?

 

[Hoefler]

You may of had some moisture in it and froze. Also, plastic expands and contracts with temperature as well.

 

[Prairie Dog]

There was a good write-up on this a while back. It may be the splines in the door are wearing out. When this happens the door can become intermittent.

 

[Crunch]

There was a good write-up on this a while back. It may be the splines in the door are wearing out. When this happens the door can become intermittent.

Thanks. I'll look for the write-up. One other thing I've noticed over the last year is that tiny to small pieces of foam rubber have been blowing up through the defrost vents and landing on the dash. As long as it is working to any extent I will probably put off replacing it (but will eventually go the Heater Treater route), and may do a dry run by popping the dash and looking at the various door components as shown in the Heater Treater video.

 

[Shadrach]

My 03 did the same. I heard a clunk back in Dec when I swithced from floor to defrost and then only had vents. I didn't drive the truck until last weekend and I had defrost because thats where I had left the knob. It worked so I didn't touched the switch. I think I'll drop the heater motor and see if I find any pieces. Shadrach