A refrigerant leak may develop from the AC evaporator causing the AC to blow warm air. Verifying failure of this component is difficult. A good shop will use leak detection dye to verify a failing evaporator.Google+
Car Problem Reports
Honda Civic AC Evaporator May Leak
Honda Civic Problem
Average Mileage: 127,000 mi (80,000 mi - 175,000 mi)
Visitor, 2000 Honda Civic, 126,000 mi
My a/c had been blowing warm for about a year, but I thought it just needed a re-charge. I took it in today and they diagnosed it as a leaking evap, which also explains the odd, moldy smell that has been permeating my car since around the time the a/c stopped working.
Visitor, 2007 Honda Civic, 80,000 mi
ac blows warm air, when the ac is on the car idels fast then slow and the headlights dim then get bright then dim this goes on the whole time the ac is on. Also when I come to a stop the car shimmys like its going to stall.
Visitor, 1996 Honda Civic, 175,000 mi
Windows were fogging up when using air, then noticed "fog" coming from vents and a leak in the passenger floor board. Apparently it is a bad evaporator/heater core. Very expensive to fix. Not sure if we even will. I mean, the car is 17 years old...so maybe it is due...but..a bummer anyway.