i had an issue with a GEM unit on one of my ex's. They would work fine after a while of the vehicle running heat. My guess is that moisture in the air was causing an issue with a weak point in the unit. But yeah, every time it rained when I came out from work or what ever it would take 15-20 minutes before i would have wipers. Major P.I.T.A. LOL Don't know about your specific situation, but figured I'd put in my 2 cents as to a POSSIBLE cause.