If you can find vacuum schematics a few years back you will see that
they added a vacuum actuator to the case called a "slave" valve, it has
a grey hose going to it from the control head.
BUT this is only supposed to exist with AUTO CLIMATE CONTROL!
I can't find anything that shows operation for the "slave" door.
What happens on vehicles with C60 manual HVAC is that the door causes
ambient air under pressure at the cowl to be forced through the heater
core making it nice and toasty and cooking the driver's foot because
the mode door rests in the "heat" position.
is what to do:
Open the glove box, lift up the wire hook and swing the
door down. Now you will see right in front of you this actuator with
the grey hose, take the grey hose off the vacuum actuator and plug the
end of it so it won't hiss or leak, tie it back so it won't rattle
around , Or I used one of those thin plastic vacuum line caps,
put it over the nipple then put the line back on it, to plug the line
and close the glove box.
You just fixed this concern, and if you think I am full of it, try all
the other modes. They are TOTALLY unaffected by disconnecting that
actuator, the heat is just as hot and the A/C is just as cold.
I think in the '96 manual comparing the vacuum scematics on C60 and
whatever auto is on the utility you will see that the grey hose and the
actuator are not supposed to exist on C60 manual HVAC vehicles.
I am not exactly sure what this "slave" door is supposed to do but I
know when you turn the HVAC knob to Off it fries your feet.
I think someone sold them on the idea they could use one case for all
units and neglected to mention that you'd have a few hundred thousand
folks with burnt toes.