A/C Heat Strip

I bought a heat strip for my older Duo-Therm roof air conditioning unit and I don't know where to install it. I know it is the correct type for my unit but can't quite figure out where it goes.
John, (Lake Ariel, PA)

John, first you must remove the plastic ceiling air distribution box. Do so by first removing the return air grills covering the filters (some units may be equipped with a single grill and filter). Once removed you should readily see two or more screws securing the plastic housing to the A/C plenum. Depending on the exact model Duo-Therm, there may be another screw behind a plastic plug on the air box itself. Very carefully pry the plug out with a small screwdriver and remove all the mounting screws.

Once you have removed all the screws, remove the ceiling distribution box to expose the metal A/C plenum. The heat strip assembly installs directly below the air discharge opening, which is that opening going up into the rooftop unit. There will be small mounting holes in the plenum corresponding to the screw locations on the heat strip. Position the heat strip directly under the discharge duct so the screw holes line up with the holes in the plenum and secure it using the supplied sheet metal screws. Plug the electrical connector on the heat strip into the existing receptacle on the AC control box. Typically the air box is notched to allow the harness to pass through it, but you may have to slit the foil or insulation or knock out a plastic plug.

Once you have made space for the power harness, you can remount the air distribution box to the plenum. Realize that add-on heat strips may take the chill out of the air, but they will not sufficiently heat the entire motorhome.