90 1/2 ton heater controls not funtioning

my 1990 1/2 ton heaters controls started to not work just since it got cold outside.the heat switch(floor to defog)will not return the air back to the defog.its stuck on floor.the vent switch seems to work fine(next to heat switch).also since this has happened the off button no longer works and the a/c switch does not work as well.Again this all seemed to have happened since the cold weather set in.any ideas.thanks ahead of time.this seems to be an intermitant problem as i remember the previous owner had this happen from time to time.

id say jus go to the junkyard or look on ebay for a new one, i found one on ebay for like 30 bucks. i thought mine was bad but i think i have found the reason y my heat dont work, i guess its some vavle stuck shut. i ahve no heat at all only cold air blows out the defroster and heater, no warm heat will come out at all but really no clue on wut it is, if neone happens to kno please tell me