My 2004 mitsubshi galant has heat from lower vents (floor) and windshield vents, but not from the dash vents. Nothing (heat nor a/c) comes out of upper vents just above the radio and near the doors. Replaced (used) ac/heater control unit..no luck. This car had a clicking noise in the vents whenever I turned the vent control knob to direct the air through the different vents...it was under warranty, but wasn't doing it all the time, so no luck there.

check vacuum lines under hood and under dash area

Blend door motor went bad or something fell in the vrnt and is jammed in the doors. If you are a decent wrench you can do it.you may need to take some of the lower dash apart and the heater box down by the floor.

its either a bad air control panel or u have a bad damper valve in your dash

If air does not come out of the defroster vents, but does from the floor and dash, it could be a blend door problem under the dash.

Possible bad blend door actuator .some gm cars can be relearned to the new climate control head

Mode Door 1.
a.This door regulates air flow to either the dash vents or defrost/floor. If you have air flowing only through the vents with no defrost or floor, this door is failing. From our experience, this door is usually the first domino to fail. Not sure why, just is.
<!--[if !supportLists]-->4.Mode Door 2.
a.When mode door 1 is set to divert air away from the vents and into the second stage of the system, door #2 chooses whether air goes to the defrost vents to the windshield or out through the floor vents in the passenger and driver's side footwells. Failure is indicated by an inability to choose between defrost and floor.
b.This door turns out to be the most difficult to replace. In order to replace the door, the dash panel has to be removed. It's still better than the dealer fix because you don't have to evacuate the AC system, drain the radiator, and remove the plenum box. But it is more work than the other fixes. When this door breaks, it falls in the down position, blocking the floor vents and diverting all air through the defrost vents. From a safety standpoint, this is good since you'd most likely rather have a clear windshield than warm feet. We suspect that a large percentage of customers will just leave this door unrepaired. You will have heat through the dash vents and to the windshield, just nothing to the floor. It's inconvenient, but you'll have to make the determination if warm feet are worth the extra work to fix the door. An extra pair of socks is easier.

check for vacuum leak some of the switch are vacuum controled

sounds like the doors that open and close that direct the air are jammed, or are not receiving a signal. Have someone run a code check which should tell you. May just need to have a faulty code erased or...$$$ repair by Volvo.

Check the brushes on the blower motor that circulates the air in the car.

Try replacing the cabin air filter.