I'm having a similar problem with my 2002 T-Bird, however it seems that it's just the passenger side that suddenly starts blowing hot air for no apparent reason.
The problem goes away when I turn the car off and then restart it, however the problem may or may not re-appear after driving for a little while.
I haven't been able to tie the sudden switch from cold to hot to any particular action on my part. (ie, fiddling with the temp controls) It also doesn't seem to be tied to driving over a large bump in the road.
Since there are separate temp controls on each side of the car, I'm assuming that the passenger side control is connected to the problem, but I have no idea where or how to start looking.
I'd appreciate any help from anyone in the forum.
Thanks,
Ray | 
