I have a 2014 Montana Mountaineer that I purchased new and the Dometic 15K ducted air conditioner quit blowing cold air. I took it to the local Camping World and they told me its the compressor and that the entire unit has to be replaced($1200) because its a sealed unit.
After checking with the three Dometic dealers in my area, I pretty much got the same story from them all. $1200 to install a new unit.
I contacted Dometic and they honored a manufacturer service bulletin and replaced the unit even though it was out of the warranty period. I had to have one of the Dometic service centers send them the diagnostic information and I had to pay the installation cost. So I had Camping World of Mid-MO who did the diagnosis send them the information. Dometic sent them a new unit within a few days and Camping World installed it for $172. I am very happy with the customer service of both Dometic and Camping World of Mid-MO. I have always gotten great service on any repair I have had done at Camping World.
As for Keystone, not much help.