What would cause ice to form on the fan blades of the outdoor unit in the heating mode? Unit is not being dripped on from overhead. There are no exhaust vents nearby. It is a 6 year old Bryant that has done this since day one. It only happens a couple times a year and only when it rains or snows. It ends up throwing the blade out of balance and the unit shakes like a cat sh!tt!ng tacks. The HO has to pull the disconnect and melt the ice with a hair dryer. There have been no other problems with the unit. Original fan and blade. I have not seen this unit. The owner is one of my students grandfather. Thanks for any insight.