Air conditioner blows cold air out the defrost vent under power not the front vents.

Could be a blend door problem under the dash.

Could be a blockage in the lines to the rear unit.
Might be low on freon too. Or a blend door problem.
Can you check under the floor and see if one of the lines is cold ?

International 9400 9200 9900 heat box is under the passages side seat. That where the heater core location and the ac evaporator blower. You have two control motors under there one control the bunk for hot and cold. The other control front for hot and cold. Defrost vent and front vent is in the dash. My suck on defrost and in floor will open to front vent. I have not locate yet.

Check the duct work under dash might be unhooked

if both vents are blowing air in general then you may need to get your air conditioner recharged, but if the front vents aren't blowing at all then you may just have a jammed vent flap and you can fix that from under the hood next to the blower motor. check you rowners maual for the exact location

It works off of vacume. The butterfly in your ducks arent opening, to allow the cold air to pass. good luck .

Your last guess is probably the right one. The deflectors/directors are vacuum controlled and you may have vacuum line either broken or disconnected; these aren't fun to find. I would start under the hood and make sure the vacuum reservoir is intact (have seen them cracked) and then start tracing hoses from there.

you have a vacuum loss to the ac control head, the motors that divert air are vacuum operated, if you loose vacuum the system goes to defrost for safety reasons, the vacuum comes from the engine, then goes o a plastic vacuum tank under the hook start there, it is a 3/16 id hose.

common problem, check under dash by the gas pedal if control arms are muving went selecting from ac to heat cuz this it is the control for the vents to go from ac to heat and to defrost.

Had the same problem. believe it or not i changed the gas cap and got heat all around. something about pressure.