I just had a goodman furnace installed, but I think the installers are trying to pull one over on me. First there is no return installed, the fan is exposed on both sides and they just installed a vent in the closet wall where the unit is being stored, does this seem correct, because I refuse to pay until it is inspected but I am curious because every thing I have looked at this install seems incorrect.

Did the original install have return ducts? Where is the filter? In slab houses with an install like you described it is.common to have a single return. However, if you originally had a ducted return system there is no reason to not have the new unit connected like the old.one .

It's new constructon, that's the problem, there is no filter, the put the filter on the wall of the closet where the furnace is located, I don't see how that's filtering the system and according to goodman if there is no filter then the warranty is voided, I think these guys who did the install don't know what they are doing, they were hired by the builder

There obviously has to be some flow through the filter or why put it on the wall? Sure there is not a return grill somewhere? Post a picture.