I just replaced my enginer (Ford Windstar), when we picked the van up and placed the AC switch to Max AC or any other position for that matter, the air in the front blows cool air only out of the defrost vents and the air in the rear blows Hot air at the lower vents (near the feet). What would cause this to happena nd could it have happened under the hood somewhere when the mechanics replaced the engine and reconnected cables and hoses, etc??