Can an central air conditioning and heating unit be some how cross connected and the condensation just recurculates through part of the vents causing mildew.

We have mildew in the front part of our condo but not in the back part. It is just in the vent and return areas of the living room, one bathroom and one bedroom.

Mildew is caused by moisture and dirt. You can have your duct system checked but I doubt if that is the problem. Check for a restricted drain line and clean the coil.