Lost vacuum at defrost & vent & floor control.

Which vents, floor--defrost--dash? Can you hear the blower motor running? The squirrel cage could have broken loose from blower motor? There could be an actuator problem under the dash? If actuators are vacuum controlled and vacuum is lost, it might default to defrost, only blow out defrost vents.

check emissions vacuum for disconnected lines as most climate controls use vacuum baffles for air flow..

defrost is the defalt mode look for a damaged vacuum line going ti the control head

Usually a blend door problem. You will need to check the power source for the door and its operation.

There is no vacuum to the controls. Look for a vacuum hose that is no longer connected to the engine intake manifold and repair it.

Vent control has lost vacuum since that is what powers it. The default direction is the defrost. Pul radio sectiion and look for a loose hose.

There is a vacuum leak under the hood. Find the vacuum line on the passenger side where it comes through the firewall and follow it to the engine. You system needs vacuum to operate and without it the default setting is on defrost for safety reasons.

Does it still blow out the floor and defrost when you set the switch to those positions or does it alway blow out the defrost no matter what? If you can get air to blow out to the floor, then it sounds like you lost the switch that controls the airflow to the vents. If it only blows out the defrost, then you probably lost the vacuum to all of the switches. When the vacuum is lost, it will only blow out the defrost. Check the smallest line on the vacuum distribution block located in the corner near the brake master cyclinder. That line provides the vacuum to control the direction of airflow within the cabin.

U have either lost the vacuum to the mode selector switch (in the dash control) or the vacuum mode selector switch is leaking in the ac/heater control in the dash, u can usually hear a hiss if it is leaking. the vacuum source is the engine, a small hose runs through the firewall on the passenger side to the switch from the eng vacuum source.

Sounds like you have a supply vacuum problem. When you lose supply vacuum to the control head it defaults to defrost.