13.5 to 15?

Get reflectix for the windows. It keep a lot more heat out that just having your drapes or shades pulled. Putting some behind the drapes for the windshield of our coach made a 10 degree difference on the inside temp.

I upgraded from 13.5 to 15K and though it helps a bit. Still HOT

j-d wrote:
We have Coleman Mach 15 as our single A/C, not Ducted. Also have MaxxAir's nice heavy duty shroud on the rooftop part of that Mach.
Related to Pool Noodle, I found that the required Foam Baffling for the two edges of the Condenser (coil you see from the rear) didn't migrate to the Mach when the Shroud did. TuffMaxx or something it's called, good solid shroud!
Anyhow, Hot Air was being drawn back into the condenser. A/C overheating and shutting down. Wouldn't overheat with the Shroud off. I even made a temporary "roof" to cover the unit leaving the sides open. Chris Bryant warned me about the Foam Baffles and out came Pool Noodle and Pocket Knife. Problem Solved!
Many Many Many RV's waste their A/C in Bad Ducting. Almost makes me glad we don't have it. Investigate 1. Design, 2. Installation and 3. Deterioration. Then see if you have adequate cooling.
Fifths have a lot of "cube" inside, so 13.5 is probably marginal. When you serviced it, did you clean the "indoor coil," the one in the Front of the A/C, that you have to take some internal shrouding off to access?

I'd dispute "bad ducting" and say, instead, "bad build", or even "typical build". :(

Lyle

We swapped our 13.5 for a 15 the second year we owned our Outback. It's 35 feet long and 3 slides. It made a big difference. This last week-end temps in central Indiana reached near 100 degrees. Ours did just fine. Of course, it was running first thing in the morning and we never turned it off. By 5:00 pm when temps maxed for the day, we were still quite comfortable.

One trick we learned with our previous 13.5 air conditioner; if the temps get too hot for the air conditioner to keep up comfortable, then retract one of the slides.

Our bedroom slide is a closet slide. It was the first to be closed. Our living room has 2 opposing slides. When temps got too hot, we'd close one slide in the living room. This reduced the square footage tremendously and the 13.5 kept us from roasting.

We haven't had to do that with the 15,000, and keep all 3 slides out. We do occasionally use the center air blast instead of the ducts. This blasts all the air directly in the living room and right where we sit. When coming in from outside, that instant blast of cold air is like getting hit with a bucket of ice!

I have found that if I run my 15K AC thru the ducts the trailer gets hot. If I bypass the venta and direct the cold air straight down the trailer cools much better. Of course I also run my ceiling fan which helps stir the air. But you have to remember, low to none insulation, small BTUs, lack of air flow all contribute to the actual problem. More, way more BTUs may be your only solution.

28 foot unit should have 2 AC units in hot climates. Going to a 15k will give you about 15% more cooling capacity. I would go the 15k route first and then keep the 13.5 as a spare if I decided to add a 2nd unit. Doug

If the 13.5 is working properly, don't expect much difference.

Can you close off the vents to the bedroom? We used to do that and that helped a lot because it only had to cool 2/3 of the trailer. By night, it was able to catch up and the vents in the bedroom were reopened.

We have Coleman Mach 15 as our single A/C, not Ducted. Also have MaxxAir's nice heavy duty shroud on the rooftop part of that Mach.
Related to Pool Noodle, I found that the required Foam Baffling for the two edges of the Condenser (coil you see from the rear) didn't migrate to the Mach when the Shroud did. TuffMaxx or something it's called, good solid shroud!
Anyhow, Hot Air was being drawn back into the condenser. A/C overheating and shutting down. Wouldn't overheat with the Shroud off. I even made a temporary "roof" to cover the unit leaving the sides open. Chris Bryant warned me about the Foam Baffles and out came Pool Noodle and Pocket Knife. Problem Solved!
Many Many Many RV's waste their A/C in Bad Ducting. Almost makes me glad we don't have it. Investigate 1. Design, 2. Installation and 3. Deterioration. Then see if you have adequate cooling.
Fifths have a lot of "cube" inside, so 13.5 is probably marginal. When you serviced it, did you clean the "indoor coil," the one in the Front of the A/C, that you have to take some internal shrouding off to access?

I pulled my vents off and the ducts ran well past them so most air was going to the roof. I cut a piece of pool noodle stuffed it at back of vent, taped over it and my AC has been great ever since. Best $5 investment ever. The difference in air flow is amazing. Before you could barely feel any airflow with you hand at the vent. Now you have to turn the vent to direct the airflow away from the bed

You might not need a new AC. From Kestone forum:

PSo I've been asking questions lately about adding a 2nd a/c to our new 2016 31sqb. The single 15,000 btu has just not been cutting the heat of our Ky summer.
Before taking the plunge to add another unit, last night we pulled off all vent covers and the main A/C panel and began to clean up and better tape off duct work openings. To back up a bit, the air flow has never (3 weekend trips so far), felt very optimal. The master bdrm and bunk room just felt weak. So anyway, when we start really examining the bunk room vent we were stunned to realize that the duct for that vent continued more than 4 feet past the vent to the back of the TT with no more vents. Just flowed back there to nothing? Then, we checked our master bdrm and same story.....about 3 feet of dead space it went to past the vent with no where really to go.
After a trip for supplies, my husband blocked off the back sides only of each vent with some thick styrofoam type product and neatly foil taped it all off. Now, those two vents essentially have a dead end at the vent rather than several feet beyond them. As soon as we got it all out back together and turned it on we were amazed! Saw dust was coming out in both rooms and going everywhere. Apparently the air flow was so weak before, it never even stirred up that dust that was there from construction until we did this!
All this being said, the true test will be our next hot weekend trip. We may still end up needing another unit but this is bound to help!!