I believe that pushbutton unit is all electronic and doesn't suffer
from the cracked solder joints the older ones do.
Check the solenoid on the monovalve -- if the old one was badly torn,
they can leak into the actual coil area and the resultant corrosion
will cause them to stick open.
An intermittant fuse will do this as well -- replace the ACC fuse
(blower fuse is separate). No power and it defaults to full defrost
and will fry you. If the hot air is coming out the center vents rather
than the defrost vents, it's either the monovalve or the pushbutton
unit -- test the monovalve by applying battery voltage to the
terminals. If the heat goes away and the valve clicks on and off with
voltage, the PBCU is bad, replace.
Also inspect the wiring, of course, since the valve is held CLOSED by
current, not open....
Peter
