I recently installed an american standard 4 ton 14 seer 2 stage variable speed gas furnace. After installing it I noticed that the air comming out of the vents was very low. After scratching my head for 3 day and talking to tech support I finnily figured out the Problem. The polarity was reversed on the indoor unit. After I changed the polarity the blower blew like a champ. Has anybody ever heard of this?