Every few months, only warm air would blow out of the vents (even in the coldest setting). A simple A/C recovery and recharge would fix it, but would blow warm a few months later. Went in for a diagnosis at Pep Boys and they injected the system with dye and ran it to check for leaks. They found that the EVAPORATOR CORE was cracked on the side with the low/high pressure connections and was leaking refrigerant.