When I was a teenager I had a '68 Barracuda with an ancient "Frigiking" underdash unit. I had a toggle switch to control the compressor, so if I left it on the evaporator would ice up. I found that cycling the compressor off before the evaporator became encased in ice made things much easier. About every ten minutes I would shut the compressor off for a minute and all would be fine. If I forgot to shut off the compressor for fifteen or twenty minutes, the unit would start blowing water vapor. By this point there would be a considerable amount of ice on the evaporator and it would take much longer for it to thaw. The moral of the story? Try switching to economy briefly before the evaporator freezes, and you should be able to avoid shutting off the air entirely. Not an actual fix, but it should make things more bearable in the meantime.

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1982 300D, black w/ palomino leather, 203K
2001 E320, champagne, 105K (Mom's)
1999 Dodge Dakota, squeaky & battered, 142K