I am sorry, I am not technical on this stuff, but we had the same problem on our 95 Mustang GT. We had to take it into the dealer and the problem was that one of the hoses had come loose, so it was not blowing enough air pressure to force the vents open.
It is probably the sound of the defroster fan.
when the defroster is turned on, it activates the a/c compressor. the clutch may be locking up on the compressor.
The fans will probably stay on while the defroster is on because the A/C compressor is running.
comp may cycle when you have the defroster on
I believe they come on when the rear defroster is turned on
No. He dosn't. Besides it was Hawkeye that would have turned into one.
The most likely reason would be because you also have the defroster turned on with your heater. The defroster causes the A/C compressor to kick on which helps remove extra moisture in the air keeping your windows from fogging. The A/C compressor is linked to a "kick up" that brings the RPMs up to keep your engine from stalling due to the extra load possibly causing a surge.
The defroster is drawing more electrical current than the alternator can produce. It could be that the belt is slipping and the battery is margianally low so that when you turn on the defroster the alternator can't keep up and the battery isn't able to provide enough current to keep the ignition operating.
Turn the AC or the Defroster off.
The air conditioning will turn on with certain heater settings, typically any setting that mixes with the defroster. This to help remove moisture and improve the effectiveness of the defroster.
Turn off the defroster and see of the fans are on still. Also listen closely, do you hear the Air Conditioner on whenever the defroster is on? Cute huh? It ensures that your A/C gets turned on once in a while, to keep its seals lubricated.
Gas is turned into a liquid through condensation.