Atfeller,
You caught me at a good time, good internet!
Sorry your having trouble. I've got the post prepared below. Not sure if the pictures will post. If not, I may have to re-post or edit as required to get everything shown. The pics are important.
Start of copied MOC post starting now:
There are a variety of model numbers with this design. Ours is a 541916. I think the marketing name is Blizzard NXT 15,000BTU. The unit looks like this. This unit is typically installed in the rear position but I have worked on Heartlands that have them in both front and back. The only way to know you have water intrusion is to hose your A/C down and remove the inlet grills and filter. You can reach a finger into the outboard aft corners of the opening and feel for water but I recommend using a flashlight and mirror to have a peek in the duct. Have a bucket in place just in case.
Water can get in from rain through the seam shown in the next image below. There is no flashing (overlap) designed into the top cover and rain can run directly into the inside bay where the A/C equipment resides. This in it's self would not be so bad as there are plenty of drain holes outside the roof seal. However, the designers failed to recognize that they have alternate mounting holes that can end up inside the return air duct on most installations.
Dometic recommends sealing these mounting holes along with raising any harnesses in the area so they do not lay in puddles. All I have seen are fine on the harness. This work is accomplished after removing the forward styrofoam upper insulation and will require replacement of the sealing tape and putty. See the image below for the 2 areas as indicated by the 2 outboard arrows. The 2 inboard arrows mark the area where I do additional sealing as explained below. (Vehicle forward is down in the image.)
I'll try to explain why you need to seal underneath, inside the duct as well as best I can. There are 2 layers of plastic here about 3/8" apart vertically. The mounting hole is drilled through both layers. Then a rivnut is installed in the top layer only and the lower shank of the rivnut protrudes into the lower hole but does not fill it. Water gets between these 2 layers and is able to drip past the rivnut shank into the bottom hole and thus into the return air duct. The RV techs I've spoke with have only sealed the upper hole and said they have had no returns. However, one tech that works at a dealer had the opportunity to test one after sealing and sure enough it was wet in the duct, much less but still wet. He convinced his boss to let him add the extra sealant I had discussed with him previously and further testing saw no water. I never advocate sealing a leak from the exit but you really have no choice on this case and there is very little pressure built up by the pooling water. So, in this last image you can see the additional silicone added to the underside of the mounting hole which is actually in the upper aft corner of the return duct. Hope this all makes some sense for those interested.
As far as warped roofs? Maybe, but this is a problem for sure if this A/C unit is installed.
John
