Don't know what vehicle you have but, sounds like the duct work came apart for the middle vents.
the ducts can not be hooked up for the vents to work
vaccum losss
Vacuum leak
The mode door actuator has failed. We have instructions for repair at www.trailvoy.com
it would depend on the year of the accord. Does the defrost work or the heat in the floor work if so the line for swapping control is either broke or has come off. you can check the lower side by looking in the drivers side under the dash.
The selector mechanism needs repair or the doors inside the vent are jammed.
Most temp blend doors have an electric actuator. The defroster, dash vents and floor vents are usually run by vacuum.
The climate control is not operating for the passenger side. Check to insure the physical controls work, and the diverter vents are opening to let the cool air to the passenger side.
When there is a problem with the vent system it dfaults to the defrost setting. Sounds like you have a problem in the doors that direct the air flow.
If the floor and defrost vents are both operating and you can't change air flow to any other vents, the dash control unit does not have a vacuum source. This vacuum comes into the cabin from under the hood. Look for a black plastic line coming through the firewall near the blower motor on the passenger side. This line should attach to a vacuum canister. The canister is generally round black plastic. What usually happens is the vacuum hose gets knocked off or the plastic line may break.
The a/c - heater controller is out...........
probally closed or clogged