Rv air conditioner sealing (units using standard gaskets)

[david craft]

I looked around to see what I could find on the subject.  Trailer life had a good article, I thought could just advise people to read that and I could just expand on what they said.  Its call "Trailer life roof air leak repair".  If the air conditioner frame touches the roof then its gasket replacement time.  They are designed to drain out the bottom of the pan and touching the roof restricts flow of water.  That's why you NEVER seal the outside edge of the pan.  Also, the pan will rub the roof metal and wear a hole in it if its in contact with the roof.  Most Older coaches had a flat roof which only get concave over time generally, but there are a few tricks. I use a Vaughn bar to gently pry with and a 2x2 fulcrum if they are stuck good. If caulking was used on the gasket, I have one person pry to get separation and another inside the coach with a freezer knife cut the gasket and jointly work around the AC.  Caution and co-operation are advised here.  After the unit is removed, I use line of sight or a straight edge to see how much drop is in the roof. Measure this with a tape measure at the ac mounting point.  Anything over 3/4" needs help.  If water stands in the pan, then you can have a leak.  3/4" is the most you get out of one gasket.  If the roof metal is not laminated then you can shim.  But, I like to do more than just the gasket area.  I like to cut a board to catch the rafters supporting the compressor.  This can be inserted diagonally and tapped around into place.  3/4" is the most I have shimmed.  If you have a laminate roof, then I have stacked gaskets. The article mentioned the all black gasket, but Ive found the Coleman to be the best. Grey on three sides and white towards the rear.  When I stack I put one gasket down on the roof and caulk the outside edge, then one on the AC.  Finally mate the gaskets with caulk so they wont slide.  Cinch them down a little and make sure they are square.  Let the caulk set and then torque a little more.  The Coleman gaskets wont collapse more than a 1/4", giving you 3/4" of gap per gasket.  They are that dense.  Get the densest gasket you can.  Be sure make collar air tight so no air escapes from the supply side to the return air side.  I like the rest of their article.  Be sure to always use an RV extension cord and heavy adapter for good operation.  You can check a plugin in the coach while the compressor is on...you need at 106 volts...snow left on a roof will melt at the warm vents and AC and pool water and leak as well...