I just got a call from my wife and she says that, when she turns the AC on in her '92 Sentra XE, a fine mist or smoke is coming out of the dash vents. It dissipates when she shuts the AC off. She says it doesn't rally have a smell to it. What could this be?

possibly a freon leak or could just be the evaps not draining. Have her turn the a/c on and leave it idle for awhile. come back and look under the passenger side of the car on the ground for a puddle of water. if there is no puddle after the a/c has been running for 20 mins or so you might want to check the drain for the evap as it might be plugged up and the water is getting picked up by the blower motor and sprayed out the vents.