300D 1977: SERVO UNIT

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 rebuilt units.

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 such leaks.

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.

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 rebuilt units.

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

such leaks.

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.

If you choose to have the coolant by-pass the servo then you must also "jump" the cold engine lock out which is a bi-metallic vacuum switch on the very bottom of the servo. It is ON only after coolant warms it, otherwise it's OFF. By-passing the servo would leave this switch cold and the climate control system would always be OFF. "Jumping" the vacuum switch is done by coupling the two vacuum lines.

Thank you very much! You were so helpful!

Alex

Where are you finding the servos for around $400? everywhere I've looked they are $700-$900 rebuilt.

Try Geroge Murphy at Performance Analysis in Oak Ridge, TN. he rebuilds them with an Aluminum housing.