Thor Rooftop A/C not keeping up with heat

[Jimbo56]

Originally Posted by Judge

For all of the complaints about people having A/C issues in their coaches, I have to say I still could not be more pleased with the performance of the A/C in my ‘20 Magnitude SV34 after all the mods I did about two years ago.

After more than two weeks on the road during our current trip with temps running from 85 - 97 and having sites in full-sun with no shade, I can say the coach has been anywhere from comfortable to downright chilly.

I didn’t even bother putting in the insulated cushions in the fan vents and the A/C still performed great. With outside air temps at 95, the air coming out of my vents was right around 56 - 57 degrees and mid to low 70’s in the center of the coach. Now humdity levels were low but I got similar performance last year when temps were in the 90’s and the humidity was high.

Insulating the evaporator enclosures on the roof, cleaning up Thor’s cappy ductwork, installing an RVAir Flow in the the front A/C, closing the curtain in the cab-over bunk and using the WeatherTech F550 Full Cab Sun Shade Kit keeps my coach as cool as I could hope for in an uninsulated box on wheels.

Installing the RVSoftStarts this year let me run both A/C’s when we only had 30A service at one site as well.

The mods also help me run one of my A/C’s off my new Inverter and keep the coach comfortable at night as well without having to run continuously when we boondock a night here and there.

I have to give my A/C system a 9 out of 10! [emoji106]

How difficult and time consuming were the soft starts to install. I’d love to see a picture of your evap insulation.

[Judge]

Originally Posted by Jimbo56

How difficult and time consuming were the soft starts to install. I’d love to see a picture of your evap insulation.

It took me about an hour to do both A/C units. It was a pretty straightforward installation. I originally wasn't going to install them because my new Inverter could start the A/C without an issues. But I got them for a good price and wanted to have the ability run both A/C's the few times we only have 30A service.

I will have to look to see if I took any pictures of the insulation work I did on the evaporator enclosures. I can't remember if I took ay or not.

I used this Frost King Self-Adhesive Duct Insulation.

https://www.amazon.com/gp/product/B0...KIKX0DER&psc=1

It was also very straightforward. I removed the cover and then started applying the insulation to the flat surfaces and trimming as necessary until all of the evaporator enclosure was covered. I then used a piece of pipe insulation over the pipe that runs from the compressor to the evaporator.

[Judge]

I’m getting the best test of my A/C that I have had since I completed all of my mods and upgrades a couple years ago…. and it is passing with flying colors!

I’m down in Phoenix where it is 100+ with no shade or clouds overhead. The A/C temperature sensors (under the cabinets and against the walls) are saying 83 up front and 78 in the bedroom but I know it is much cooler than that. I just turned on my digital thermometer in the kitchen and it is 74.1 degrees in the centet of the coach! I’m more than 25 degrees cooler than the outide air temps with the sun beating hard on the roof and sides of the coach.

I did install the insulated vent pillows… plus all the blinds are down, the curtain closed over the cab-over and the WeatherTech cab kit is in place. I don’t have a cover for the shower skylight so I do get some sun and heat in there but not enough to worry about.

I couldn’t be happier and don’t think I could squeeze out any more performance from the two 13.5K units at this point.

[MLP]

Sounds about right. Try 112 degrees. We now have 15k BTU up front and the OEM 13.5k BTU in the rear. Added a outside snap shade up front and side windows that made a difference without shade. The rear AC froze up do to the 15k BTU creating a lot of back pressure in the vent system. Got to 86 degrees inside. Opened the rear AC to blow directly onto the bed. Ran a fan to blow to the front. The inside temps were 84 degrees at 112 outside. So 28 degree differential. Can't do better than that. Our paint has a lot of black so that does not help. No vent pillows and the wife does not like me to cool the rig until the temps are above 78 degrees! I like it cool and she likes it hot, but not over 82 degrees and cannot under stand why the AC's in the RV cannot cool it better! Don't even try to explain it to her. Like talking to the wall.

[Judge]

Originally Posted by MLP

Sounds about right. Try 112 degrees. We now have 15k BTU up front and the OEM 13.5k BTU in the rear. Added a outside snap shade up front and side windows that made a difference without shade. The rear AC froze up do to the 15k BTU creating a lot of back pressure in the vent system. Got to 86 degrees inside. Opened the rear AC to blow directly onto the bed. Ran a fan to blow to the front. The inside temps were 84 degrees at 112 outside. So 28 degree differential. Can't do better than that. Our paint has a lot of black so that does not help. No vent pillows and the wife does not like me to cool the rig until the temps are above 78 degrees! I like it cool and she likes it hot, but not over 82 degrees and cannot under stand why the AC's in the RV cannot cool it better! Don't even try to explain it to her. Like talking to the wall.

The temperature delta to check A/C performance is really meant to be measured based on the warm return air temp into the A/C and the exhaust cool temp coming out….. and not the delta between the outside temp vs the ambient inside temp.

In my case my return air temp into the A/C was 78 degrees and my exhaust temp out of the A/C vents was 56 degrees or a delta of 22 degrees… which is about optimal performance.

At the hottest part of the day it hit 105 today and it was still 74 ambient inside so that was a 31 degree delta…. but that is the result of both the performance of the A/C units plus the impact of keeping sun / heat out of the coach.

One of the keys is to make sure the coach is as cool as possible first thing in the morning and that as much sun / heat is blocked from getting inside the coach….. other than actually insulating the entire coach like a house.

[pohoda]

We also did most of the mods you mentioned and also made a world of difference for us. We also have one of the fans used for drying out floors etc. we picked up at Costco and run that pushing air from back to front. That air movement really makes the 2 A/Cs work more in unison. We find that the rear A/C work very well and if anything is oversized for the rear so pushing some of that cold air from the back to front really does help. We made it in 120F weather and low 100s with high humidity and it was very comfortable inside. Now if we could just get the water to run off the roof in a designated spot that would be great.