Did you clean the orifice?  Set the gas regulator on the tank( type in
manometer on yahoo,and make one for $2)?

It would be interesting to compare the ac mode results with LP.

Did you remove and clean the heating element, for good contact against the
wall of the  tube,that it goes into.Heat transfers by the contact area,
mostly( conduction). Any rust or such will insulate this transfer into the
heating chamber. Heat will have to enter the solution heating chamber by
radiation. Much less efficient.Also, make sure the heating element is
contacting the wall,the entire length of the element( about 4 inches).
Maybe a sheet metal wedge on the opposite end of the set screw to press
that end against the tube wall, directly towards the heating area.

Basically, I think some hydrogen has leaked from the ammonia solution, in
most Dometics, by now.There is not enough left to combine with the ammonia,
in large enough amounts.Liquid ammonia can be heard when burping the
Dometic,so it is still present.Did you burp it? Clogging of small passages
by operating a little too much off level is not as geat a concern as it is
usually heard.