how do i fix my amana ptca unit ?

my Amana-PTCA air conditioner heating unit shows a diagnostic code on the led screen it is a small b and a r and when it does it will not turn on we have checked the wiring at the outlet and inside it is the same unit they use in motel rooms and hospital rooms but i have it in my house does it have a master reset switch or do i need a repairman to come and fix itI just need to know what is wrong with it it is about 3 yrs old and has worked fine until a couple days ago