Ford Repair: a/c vents, vacuum hoses, windsor engine

Question
1983 Ford F150 heavy duty half-ton pickup 351 Windsor engine. The A/C will not blow out of the front vents, only the floor and defroster vents, I've checked behind/under the dash and can't seem to find the switch to turn on the vents. I've only been able to find the defroster switch and heating control switch. I'm thinking its a vacuum line not working correctly or the flapper isn't hooked up, any help is much appreciated.

Answer
i don't have a lot of info on 83 anymore but it is controlled by vacuum so first thing is to go outside in the engine compartment and find the vacuum hose going inside vehicle from engine area should be around hvac case probably going inside with wires also-also check vacuum supply to resevoir tank. if you have vacuum going inside you will have to trace vacuum hoses which should start behind glove box somewhere and go up to switches