a/c dont work, light flashes yellow

my a/c wont turn on and the lights on the consol for a/c and everything flashes yellow all the time but everything is working but the a/c. The radio is missing when i got it so not sure if theres a relay in the wiring plugs that goes into the radio that assists the a/c or what. Any help is much appreciated. 1998 plymouth voyager with 3.0 auto transmission.