The air handeler is controlled by vacuum.
Temperature may also be.
Does the air come out where it is required?
Is the temperature too cold?
The air flow is controlled by little doors, these doors are operated by vacuum motors that are controlled by the dash control which is partially an air valve to direct the vacuum to the specific motors to open the correct doors to get the resultant flow.
Depending on model, the temperature could either be cable driven ball valve in the hot water line or a vacuum motor operated ball valve.
Gas engines have manifold vacuum that works with a check valve and reserve tank.
Diesel rigs have an electric vacuum pump that is either constant running or operated via a pressure switch.
Not sure where yours is, but I suspect in the door under the driver there could be a pump under there.
You should be able to open a cover someplace to gain access to the AC air handeler, there should be vacuum hoses vonnected to motors, they look like a small roll, you can gently remove the hose from the motor and with the key turned on and moving the controls you should feel a vacuum.
The pump may be not working or a hose may have fallen off.
Troubleshoot the controls and repair problems. the vacuum motors usually last longer than the vehicle, usually a hose gets knocked off or pulls loose which results in the air going in the wrong place, in cars it is usually the defroster, who knows with the coach.
The temperature may be cool as the ball valve if vacuum operated may be in the cool position and without vacuum it will not open if vacuum controlled.
The temperature also may be effected by your coach heat if it is Aqua-Hot type.
Tony & Lori
1989 Country Coach Savannah SE