The blower on the inside, should always be blowing out of the vents when it is operating. Some blowers have two speeds. It may be that one of the speeds is wired backward, which would cause the fan to run backward when it changes to a different speed.
Unless someone wired up your fan blower wrong, that's impossible for it to suck air in the vents & the drain line & blow in reverse. It could be possible that one of the valves directing air is not operating properly & give you the illusion that it is blowing in reverse.
I can only speculate, but I can imagine how one of the flapper valves may be malfunctioning & causing this. These days i guess all climate controll systems are electric so I'm guessing they have electric motors to actuate them. In the old days it was all done by cables & you could easily feel them moving back & forth.
This is a traine and is only 4 yrs old. It started doing this last summer after we had the vents cleaned as well as the coils and 4 lbs of freon added. Now the coils are a solid block of ice as well.
Unless someone
My air conditioner works fine until t et above 90 outside. Then the fan will run backwards. It blows cold air out if the top of the outside unit and barely blows anything out if the vents. Also instead of draining water into the pipe, it sucks air up into it.
