The '77 - '80 climate control has two problematic parts: the "amplifier"
(logic board located behind the glove box) and the "servo" which
controls the heat, vacuum ducts and fan speed. Both are available as
These servos are available rebuilt for about $400 plus the old unit.
This lousy thing is so intregal to the car's climate control that
nothing will happen without it. You can bypass it by routing the coolant
line past it but then, unless you also install a valve you'll have full
heat all the time. Or, if you plug the heater lines, no heat or defrost.
I've replaced several of these after their plastic bases cracked and
leaked. Some of the rebuilt units substitute an aluminum base to prevent
The amplifier gets cracks in its board and the climate control suddenly
becomes erratic and unresponsive to the controls. Rebuilds cost about
$100 the last time I checked.
These parts can be bought from on-line parts suppliers.