It's easy to be misled when checking the A/C in cold weather---you may think it's working when all you're actually feeling is the wind chill from the fan.
The most common failure is that there is a slow leak in the system, and enough refrigerant has escaped that the compressor won't engage. (there is a low pressure switch that prevents it when the system pressure is too low)
A quick check is to turn on the A/C and open the hood (engine running) If it's working, you will be able to see the center of the compressor clutch spinning (it may cycle on and off every few seconds) If it is stationary, and only the outer pulley is turning, you either have low refrigerant or an electrical problem. With the engine OFF, try to rotate the center of the A/C clutch. It should turn easily by hand. If you can't turn it, or it is very stiff, you have a bad compressor.
The car will feel a bit sluggish when accelerating with the A/C on (if it is working)
Normally, you won't hear the compressor cycling as you drive. (maybe if you're idling in traffic) The condenser has no moving parts, and therefore is unlikely to make any noise. If the A/C is working, it is normal to hear a hissing sound from the passenger side of the dash, for a few seconds, when you shut the engine off with the A/C on.
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