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 ducts can not be hooked up for the vents to work
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.
Most likely a bad or disconnected vacuum hose to the defrost/floor selector in the heater ducting.
the heat blows out the defrost when it should blow out floor vents only
Vacuum leak
the middle vents only supply air from the ac unit using a separate in dash fan. the floor and defrost vents come only from the heater
There may be several reasons why the air only blows out the front vents and not on the floor or the defrost on the 2003 Dodge Ram. The fuses may be blown, or the heating coil is not working correctly.
The mode door actuator has failed. We have instructions for repair at www.trailvoy.com
Chevrolet Camaro stopped using back windshield vents in order to reduce manufacturing costs of the newer model of cars. They had no significant function other than aesthetic.
you need to replace the vacuum.
Because the air selector died.
either you have a vacume leak under hood or the diaphragm is blown on vent selector