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Old 08-25-2021, 01:33 PM   #1
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THOR #20809
Thor Rooftop A/C not keeping up with heat

2021 Magnitude SV34. ANything over an outside temp 90+ and the units seem to struggle. THe bedroom unit can keep temp at 70-72 but the forward unit is always ~10 degrees warmer. Durring the hottest part of the day the living room/kitchen area never gets below 82 while the bedroom (open door) gets to ~72. Both units blow cold(ish) but I never hear the compressor cycle. In the evening everything returns to normal and the coach can get down to 60's. Anyone else experience this?

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Old 08-25-2021, 02:05 PM   #2
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Larry,

We experience the same thing. Not sure if the back area is better insulated than the front - I know we get a lot of heat from the front cap area. We have added insulated curtains up front to help control that heat source. But even so, the AC manual says not to expect more than about 15 degrees cooler than outside air.

"As a general rule, air entering the air conditioner will be
cooled about 15 to 20 degrees, depending on the outside
temperature and humidity conditions.
For example, if the air entering the return air grilles in the air
conditioner is 80 degrees F., the air leaving the discharge
grilles in the air conditioner will be 60 to 65 degrees F.
As long as this temperature difference is being maintained
between the return air and discharge air, the air conditioner is
operating at its capacity. If the desired inside temperature
(normally 80 degrees F) cannot be maintained, then the heat
gain of the RV is too great for the capacity of the air
conditioner. "
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Old 08-25-2021, 02:40 PM   #3
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Quote:
Originally Posted by LarryD View Post
2021 Magnitude SV34. ANything over an outside temp 90+ and the units seem to struggle. THe bedroom unit can keep temp at 70-72 but the forward unit is always ~10 degrees warmer. Durring the hottest part of the day the living room/kitchen area never gets below 82 while the bedroom (open door) gets to ~72. Both units blow cold(ish) but I never hear the compressor cycle. In the evening everything returns to normal and the coach can get down to 60's. Anyone else experience this?
Simply the put, the heat load of the coach is greater than the total cooling output of your two A/C. Easiest way to reduce the load is to park in the shade. If that is not possible, a windshield cover is the best. Windshield shades like Magne Shade make an unbelievable difference and you can still see out. 3M ceramic tint in all the windows (they even make one for the windshield) is a worthwhile investment. If you are not using the space pull the slide in; that helps some.
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Old 08-25-2021, 02:43 PM   #4
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Best thing Ive found is like you said park in the woods or wait for winter.
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Old 08-25-2021, 03:37 PM   #5
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thank you gents that was some good info and great advice. Im also going to invest in a portable a/c like the zero breeze
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Old 08-25-2021, 04:01 PM   #6
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You probably have 13.5 units so you could change to 15K. BUT bottom line is RVs have terrible insulation unless you spend far more than we did. The front cap has little to no insulation and the front windows, cap and windshields, are heat magnets. The BR is cooler because it's smaller and not so much glass in it. Outside windshield screen is better than an inside one. Legally and safely there are limits to what you can put on windshields. Bottom line, keep blinds closed, shield what you can and live with it. This winter I'm going to do some front cap panel disassembly, 1. to check cap security and attaching screws 2. to add some cap insulation where I can.
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Old 08-25-2021, 04:53 PM   #7
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I never thought about changing the ACs for 15K or 15.5K. Has anyone done this? How hard are the ACs to R&R (remove and replace)? Does it make enough difference to make it worth it (especially for summer camping)?
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Old 08-25-2021, 04:56 PM   #8
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Google rv ac hacks great ideas there. I did the one where you use 1 foam to create a v that send air directly to ceiling vents. Less than 20:00 and about an hour of time and 2 beers. Btw best thing I ever did. Ac keeps up and cools great. There is one thing you lose that is the use of the vent on ac to dump air into area fast but you will find air flow is better and return air better.
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Old 08-25-2021, 04:59 PM   #9
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I never thought about changing the ACs for 15K or 15.5K. Has anyone done this? How hard are the ACs to R&R (remove and replace)? Does it make enough difference to make it worth it (especially for summer camping)?
If you're big and strong it's a one person job. Otherwise realistically takes 2 people. Actually easy job. Remove the inside filter and housing, 4 bolts that secure the ceiling unit to the top part and lift the roof section, top part off, and to the ground. Basically reverse procedures to install new one. The thermostat, even the one touch tablet type, shouldn't care about the upgrade. Going to a heat pump might require changing the thermostat and/or reprogramming the touch pad system.

Whether is makes a difference is subjective. Doing that and improving the resistance to heat transfer will make some difference. Doubtful you'll be able to hang meat safely inside though.

EDIT ADDING; If you wanted to try it perhaps replacing the LR unit and see if you can discern any appreciable benefit. Frankly the Omni and Magnitude models are ripe for dual pane windows and I would have optioned that were it available. Some will pooh pooh the windows but I've had it in a motorhome and my last 5th wheel toy hauler, ordered it that way, and they made a difference in sound, condensation and heat transfer. I would do it again if I had the chance.
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Old 08-25-2021, 05:03 PM   #10
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Originally Posted by RCS View Post
I never thought about changing the ACs for 15K or 15.5K. Has anyone done this? How hard are the ACs to R&R (remove and replace)? Does it make enough difference to make it worth it (especially for summer camping)?


If you are handy and have a way to safely lift 100+ pounds to the roof it is a simple job. Im not sure youll find a huge benefit but it also wont cost you very much as you certainly will be able to sell your old unit to someone who wants to add a second unit. It might be easier to just live with what you have unless you are always in super hot climates. Do you cover your windows and start your A/C before it gets hot?
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Old 08-25-2021, 05:13 PM   #11
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Pete,

Yes, in the hot climates, we always cool the rig down in the morning and keep the shades down. Thermal curtains help a lot to keep the heat from the front cap out of the living area during the day. Running the ACs off the generator while driving also helps a lot. Even so, at 100 degrees with the summer sun beating on the rig, it is difficult to keep it below about 85 degrees inside. Just looking for any advantage we can get.
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Old 08-25-2021, 05:29 PM   #12
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thank you gents that was some good info and great advice. Im also going to invest in a portable a/c like the zero breeze
For the price of one of those you could replace both rooftop units. And for what? Maybe an additional 2300 BTUs of cooling?
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Old 08-25-2021, 06:35 PM   #13
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Here's a very long but VERY good ac read
When you have a week or so it's a very good read, till then
Read pg1.

Notice the comment about the divider, taping it in place is easy to do and if yours is like most it will make a big differance! Use aluminium duct tape on side, top and CORNER and JOINT ac unit and duct.

Next big easy upgrade is to drop the vents at both ends of your mh. Block the duct just beyond the vent, this will keep the ac from trying to cool the end caps
I used this, get 2 you'll be working on the roof unit after reading a few pages of the thread.

https://www.lowes.com/search?searchT...log=4294765360

Here's the thread, I have it bookmarked

https://www.thorforums.com/forums/f2...ice-12980.html
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Old 08-25-2021, 10:50 PM   #14
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Rooftop AC units

A big problem with rooftop RV AC units is that the cold air output, the warm air return, and the cold air duct to the ceiling vents are grouped in a common space. Whoever designed them ought to hand in their engineer card.

So you have cold air blowing down on one side, trying to get to, and out through, the cold air vents. On the other side, warm air is being cycled up into the exchanger. The result is a turbulent mess that is horribly inefficient.

There are a bunch of youtube videos describing the problem and offering variations on the same solution - a hard foam gadget that separates the cold air output from the warm air return, and also forces the cold air directly into the ducts to the ceiling vents. Here are a couple:

Boost your RV Air Conditioner...

RV A/C Modification...


There's also a commercial (and really pricey!) version if you aren't a do it yourselfer. The claim is that this type of mod can double your A/C efficiency and cooling ability.

That said, RV A/C units aren't made to function like their home equivalent. If you can get the inside of your rig 15 degrees cooler than ambient, you're doing pretty good.
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Old 08-26-2021, 04:32 AM   #15
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We have not experienced any cooling issues with our XG 32 in the little over a year that we have owned it. We have Weather Tech window covers for the cab windows which has made a difference, and we have a small 12" Vornado fan that has been used in our 2 previous motor home and it makes a difference, keeps the air circulating. We put the fan in the bed room and pull the air out of the bed room and push it towards the front. We keep the thermostat for both a/c units set at 73* and they will both cycle off and on during the day.
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Old 08-26-2021, 05:58 AM   #16
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That thread abjbrtd mentioned is a good read, but it quickly dips into the hypothetical and opinion-based debate on a topic for a significant amount of the 21 pages of comments. I would still consider it the de facto thread on the topic, however. Just be patient, as there’s gold in them thar comments.

Based on that thread and a miserable 1st summer, I did a ton of mods, and now can keep my 34J at a comfortable 75-78 degrees when spending the day on a parking lot campsite and the gravel around me registering 100+.

In order of what I found most impactful:

The foam board teepee mod listed in a bunch of YouTube videos and mentioned by several folks above. I don’t know about “double” the air volume. But it is significant and a very noticeable improvement. It’s probably the cheapest and easiest mod out of the bunch.

Stripping out the old crappy tape job with lots of gaps inside the AC (from the inside) and making it nice and smooth. No more air leaks!

Using a $20 “as seen on tv” camera scope and some cans of latex foaming spray to see into every vent and fill/close/smooth every gap. Most importantly, sealing off the end run of each side of the venting chambers.

Using the spare dynomat & .75” foam insulation around all the metal housing under the plastic cowling for each of the two AC units on top of my rig.

Having done all that, at night we like it cold enough to hang meat. We actually joke about that with others when they come into the rig in early morning for a shared breakfast and it’s still 68. I also yell a lot at the kids to keep the door closed as much as possible.

I do still feel a ton of heat radiating off the windows, though. So I have a roll of Reflectix sitting in the garage, waiting for our next trip. I plan to make window shades for at least the big front windows and store them under the drop down bunk when not in use. That should get me to my desired 72 in any weather goal….
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Old 08-26-2021, 09:37 AM   #17
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THOR #22586
Quote:
Originally Posted by abjbrtd View Post
Here's a very long but VERY good ac read
When you have a week or so it's a very good read, till then
Read pg1.

Notice the comment about the divider, taping it in place is easy to do and if yours is like most it will make a big differance! Use aluminium duct tape on side, top and CORNER and JOINT ac unit and duct.

Next big easy upgrade is to drop the vents at both ends of your mh. Block the duct just beyond the vent, this will keep the ac from trying to cool the end caps
I used this, get 2 you'll be working on the roof unit after reading a few pages of the thread.

https://www.lowes.com/search?searchT...log=4294765360

Here's the thread, I have it bookmarked

https://www.thorforums.com/forums/f2...ice-12980.html
Thanks for the links. What diameter pipe insulation is needed and about how many feet per unit. Did you also use mat that you cover the "box" on top, and how much of that per unit?
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Old 08-26-2021, 11:21 AM   #18
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I have a 2020 SV34 and after a weekend in 90+ heat in Nashville last weekend I am very happy with all of the my A/C upgrades that I made in the past two years.

Here is my formula for success.....

- Full WeatherTech Sunshade Kit in the cab.
- Curtains pulled closed in the cab-over
- Camco Vent Insulators in all 3 vents
- Blinds down
- Evaporator units insulated on the roof
- Compressor output plumbing insulated
- Styrofoam ducts trimmed in ceiling under vents
- Sprayfoam closing of ducts at front cap and rear cap vents
- RV AirFlow unit installed in front A/C unit to divert more airflow to bedroom vents so the bedroom A/C unit does not need to be run at night when sleeping (never ran the bedroom A/C at night with lows in the mid-70's at night).

It was 95 on Monday and the feels like temp was 100 and we had very little shade in our spot. The front of the coach got no warmer than 78, which felt like a freezer compared to outside.

The best part is how fast the coach cools down. We were driving the other day and temps were in the mid-90's. The temps were in the upper 80's in the back so the DW started the generator about 30 minutes before stopping for lunch and by the time we stopped the temps were in the high 70's.

You also after to remember the temperature reading is slightly deceiving. The temp sensor is under the cabinets close to the wall where the heat is higher than the center of the coach.
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Old 08-26-2021, 12:26 PM   #19
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Originally Posted by chunker21 View Post
Thanks for the links. What diameter pipe insulation is needed and about how many feet per unit. Did you also use mat that you cover the "box" on top, and how much of that per unit?
We have a Dometic so yours may be slightly different.

I used the smallest id Lowe's had, 1 piece will be plenty.
I used the rest to block the ends of the ducts

We have a pretty good styrofoam box around our coils I covered the seams with aluminium duct tape, same as the return and output in the inside.

Supper easy, cheap and effective.
If you can take some pictures on the vent temperatures before and after and post them.
Anybody following this thread will be pleasantly surprised
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Old 08-26-2021, 01:05 PM   #20
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Originally Posted by abjbrtd View Post
We have a Dometic so yours may be slightly different.

I used the smallest id Lowe's had, 1 piece will be plenty.
I used the rest to block the ends of the ducts

We have a pretty good styrofoam box around our coils I covered the seams with aluminium duct tape, same as the return and output in the inside.

Supper easy, cheap and effective.
If you can take some pictures on the vent temperatures before and after and post them.
Anybody following this thread will be pleasantly surprised
Thanks I hope I can get one at least taped before next week's trip. They are Coleman. I'll make the pictures as I can. Motorhome is under a pole barn and not in direct sunlight so that will affect the results based on other's mods and performance. I'll reiterate than when I post my results. It is hot though, lower 90s.
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