Blower/Heat Problem

My 98 Grand Prix GT (3.8 non-SC) with auto climate controls has a strange heat problem. My blower is working fine, with plenty of air flow when set to cold air. When I turn the knob to get hot air, my air flow drops down to 10% of what is on cold. The little air that comes out is warm. This happens on all the vent settings (dash, floor, defrost).

Suggestions? Is it the climate control unit? Some sort of damper that directs air flow? Can the heater get clogged with debris? Thanks in advance.

I would look for debris first (and if present, install a cabin air filter from a 98 Regal), but the actuators could be the issue too. Does it switch properly from floor to vent to defrost modes?

The controls to switch from vent to floor to defrost mostly work. However, combined floor/defrost setting usually blows harder on the windshield than the purely defrost setting, so maybe that's a hint that the actuator is a problem. What would this entail fixing? Would the actuator itself need replacing, or perhaps an air line controlling it?

Thanks for your input.

Bump.