I live in a NM desert. I live with triple digit heat every summer (over 105F most days and as high as 135F).
There is probably nothing wrong with your unit. The techs are probably tired of telling people that air conditioners don't like triple digit heat (no one ever believes them). Also they only cool 20 to 35 degrees cooler than ambient temps. Most of the RVs in my park have sprouted "window shakers" when their rooftop airs pooped out (some have burnt up the compressors). Not all RV parks will allow window shakers. Did I mention the rolling brown outs kill compressors? Our local power company says we don't have rolling brown outs. I guess it's just our imagination.
Compressors don't like to run when ambient temps are high. Whether it's in a refrigerator, freezer or air conditioner, they all have a limit and they will stop. Sometimes permanently. The only way you will keep a compressor going in these high temps is to be pulling the air for cooling the compressor from under your rig where it tends to stay shady. This is where some of the DIY builders were pulling their exterior air for the mini-splits they installed in the basements of their coaches. But even that has it's limits.
I have two 6000BTU "window shakers" that were built into the fore and aft bulkheads of my bus (you can't see them). The bulkheads double as plenums to bring air to the compressor. But when the exterior temps are above a certain point, the compressors will shut down to 'save" themselves from burn out. The fans keep going but the compressors stop. I just plan for it.
1) I have a reflective roof coating on the roof. I renew it every so often in the fall (recoat at the end of the "warranty" listed on the can).
2) I have a sandwich of Reflectix/cheap packing quilt blanket/painters tarp hanging on all my windows as curtains. It goes a long way to cutting down the heat intrusion (and works in the winter too when temps drop to single digits, sometimes with a "-" in front of the number). I buy the packing quilts from Harbor Freight as you can't wash them very well and I just toss them every so often. I have one hanging over the entry door too. The screens in my windows are "solar" screens which block a great deal of heat gain.
3) I do my "hot" things in the early morning. That is anything that generates additional heat, like running the dishwasher or doing laundry, before the temps rise too high. I eat my main meat at lunch because shortly after that it starts getting too hot to eat. Supper is a cold thing like a bowl of cereal with a protein shake in it rather than milk (which makes me sick because it's too hot) or a cold sandwich. Hot meals make you feel warmer.
4) I take lukewarm showers (never cold) when I get too hot. I wear lightweight "stay dry" or "moisture wicking" workout clothes. I drink iced tea all day and take my vitamins at night to replenish what I sweat out during the day. I also take magnesium glycinate at night to combat muscle cramps from loosing too much electrolytes during the day. (Different types of magnesium does different things)
5) I have the bus divided into sections. The bus has a center aisle layout. Front to back, the bus layout is salon (and entrance), galley, bathroom (split - toilet on one side and shower on the other), laundry and closet, then the bedroom. The airs are in the salon and the bedroom. I have a dog so she needs to be able to roam front to back. I use curtains (folded over flat sheet, blanket, beach towels or painter's tarps) to block off the bedroom from the rest of the bus and the salon from the rest of the bus. This means each air conditioner is cooling a very small area. I open windows (still covered) in the "hot" part.
6) I mounted several
9" floor type fans in several places, on the ceiling so they can pivot. The one in front of my residential refrigerator and upright freezer blows to the ceiling, forcing air behind the freezer and refrigerator to help keep them cooler. This helps to move the air so there are no "puddles" of hot or cold air. It helps to move the hot air out the windows in the hot parts of the bus as well. I use the exhaust fan over the range to move hot air out of the galley. The hot part of the bus gets almost as hot as exterior temps. I replace the fans every other year or so because they run almost constantly, year round.
Sites like builditsolar.com has projects and info on energy that you can use in an RV if you can figure out how to adapt some things. I got the idea for my interior storm windows from that site (my storm windows also open so they stay up year round).
I could tell you more things that I do but this is too long already. Someone, or several someones, will be complaining about the length. And I have to walk the dog before it gets too hot.
