HELP! '91 200TQ Climate Control Probs

[WILLIAM BAKER <WWB-HMB@worldnet.att.net>]

I recently bought a '91 200TQ with 94,000 miles on it.  The Climate
Control has a wierd problem.  When set on "Auto" in hot weather it works
very well, delivering cool air through the dash vents.  However, after a
few minutes, the air duct dampers spontaneously change position and the
cool air is delivered through the floor and the defroster vents. 
Resetting the CC to "Econ" causes the dash vents to reopen (after a
delay) and the the CC can be returned to cooling mode by resetting the
"Auto" mode.  Unfortunately, after a few more minutes the cycle starts
over again. I sold my '86 5000CS TQ last week that had the same problem
(I warned the buyer). 

The car came from New Hampshire and I suspect a corroded or loose
connection or possibly an intermittent sensor problem.  Has anyone
experienced this problem and been able to solve it?  ANY help will be
greatly appreciated as it's getting hot here in Reno.

Thanks -

Bill Baker - email: WWB-HMB@worldnet.att.net