so... it operates... but inconsistently, right? that points out a poor connection, chaffed wire, possible grounding, short or similar cause...

pop the inside tray that holds cassettes/CDs/or just an empty bin - it just pulls out with enough force from your fingers... look at the wires inside, they might be shorting... check to see if the airduct/tube is inserted correctly - when the bin is out, turn the AC blower on, and listen for escaping air...

let us know if you find anything... good luck