Depends on the van and the unit fitted as not all the same...............
Roof units are pretty good, depending on brand/model some can be noisy others hardly know they are working, the heating side the same while the in wall type unit is not much chop really the AC is a split system set up but not as some say a reverse cycle and the heater is just a heater element in the blower unit.
Let us know what your looking at .