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Old 06-18-2019, 04:25 AM   #1
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THOR #13937
A/C units - how cool Dow they get?

Fairly new to this whole Rv’n thing... and our Miramar has two A/C units one in the main coach area, and one in the rear sleeping area.

We had it out in AZ again at the weekend 100F+ outdoors and the units were in full blast but the inside temp never got below the high 80’s ��

Does that sound normal???

Worth noting the unit in the rear did manage to cool the rear bedroom
Area to a comfortable temp.

Surely these units should get the coach down into the 70’s.... ����*♂️

Input / thought would be greatly appreciated
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Old 06-18-2019, 10:52 AM   #2
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20 degree difference sounds about right. You can help things by covering your windows and using your awning to provide some shade. Also a shaded site would help. I have cut and fit Reflectex sheets for every window and keep the shades down. This makes Florida bearable.
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Old 06-18-2019, 03:14 PM   #3
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Model: Miramar 35.3
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THOR #6451
We have a Miramar 35.3 and live in Florida so we are always using the AC units. If we are camping during the summer, the first thing I do when we arrive at our site is to put down the windshield shade and the two side window shades. The front of the motorhome is always warmer than the back. I can usually keep the temps in the front of the motorhome in the upper 70s and the back of the motorhome in the lower 70s. I try to keep the door closed as much as I can. If people are constantly opening and closing the door, it will get warmer inside. The summers in Florida are usually in the mid 90s outside with high humidly. Being in the 100s would be much harder to cool, especially if parked in the sun.


Burch
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Old 06-18-2019, 04:08 PM   #4
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RVs do not have the same insulation values as stick built homes so cooling from the 100s to 80s sounds about right. We've added blackout curtains to the windows as well as putting those pillows things in the overhead vents. I also added insulation between the layers of the bathroom skylight. That thing was light a heat lamp on hot summer days. Our coach is a lot more comfortable on 100 plus days now than it was from the factory but the A/C units tend to run most of the day.
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Old 06-18-2019, 04:20 PM   #5
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Quote:
Originally Posted by Exilenla View Post
Fairly new to this whole Rvín thing... and our Miramar has two A/C units one in the main coach area, and one in the rear sleeping area.

We had it out in AZ again at the weekend 100F+ outdoors and the units were in full blast but the inside temp never got below the high 80ís ��

Does that sound normal???

Worth noting the unit in the rear did manage to cool the rear bedroom
Area to a comfortable temp.

Surely these units should get the coach down into the 70ís.... ����*♂️

Input / thought would be greatly appreciated
The biggest problem is your coach is taking on more heat than the A/C can remove. The easiest remedy for that problem is to always park in the shade. Of course that is not possible so windshield covers or ceramic tint on the windshield and the windows will make a huge difference IE on a 100 degree day in fulls sun my coach stayed in the low 90s with the one 15,000 btu A/C. With all windows and skylights covered with Reflectix insulation, the max inside temperature was 79 degrees. The next winter, I added a second 13,000 btu A/C, a Magne shade for the windshield and the cockpit windows. We keep the thermostat set at 75 degrees and the A/C cycle periodically except during the hottest part of the days.
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Old 06-18-2019, 08:26 PM   #6
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THOR #1808
i bet the actual air temp at the cold side of the condenser was down in the 60s or colder...the LACK of real insulation in the roof and that big library window up front, makes it a real killer to keep cool
my wife made a "heat shield" for the front to supplement the roll down shades.
its a layer of foam foil insulation between two fabrics, one side is deer the other is tropical fish
depending on the mood is the side people see, it helps somewhat
put snaps on the board above driver and it hangs off those , it rolls up and goes in basement when not needed.
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Old 06-19-2019, 01:25 AM   #7
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The other thing to consider is that you also have to cool off everything in the RV, not just the air. What we have found is that if you let the RV get to 90 while you are driving, it will take forever to get it cool again. What I've started doing is when the temperature in the RV gets in to the low 80's, I'll turn on the generator and start the air. It keeps the inside of the RV (and all of that thermal mass) from getting too hot. This way, when we get to our destination for the night, it isn't that difficult to lower the temperature in the RV from say 78-80 down to 74.

I think this was the biggest improvement in keeping the RV cool for us. And, yes, I have reflectix on the windows, a thermal curtain for behind the cab, and those popup window reflectors. Oh, and the vent added to the bottom of the air conditioner unit inside.
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Old 06-19-2019, 03:23 AM   #8
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My neighbor the a/c guy says best way to gauge the A/C performance take the temp at the outlet nearest the unit. A well functioning unit should be kicking out around 25* or more below the outside ambient temperature. So far this summer we have not gotten anything over mid 80*'s in NW Indiana. Our 15000 btu unit has been consistently 53* at the nearest outlet to the unit. BSexton hit the nail on the head get the unit cold and keep it that way.
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Old 06-19-2019, 07:18 PM   #9
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THOR #1808
let me add.
If we are the road and outside temps are near 75 or above, i run the genny and both rooftop a/c as well as the dash a/c. I like to be chilled while driving.
pulling down the night shades over windows behind the driver works well and having then drawn down once parked helps a lot as well.


these puppies are just not designed for occupant comfort at or near 100F outside, shamefully.


we also CLEAN the a/c condensor coils routinely with coil solution , spray on and let it run down and rinse with fresh water, it does wonders

nu calgon makes a great product its on amazon

https://www.amazon.com/Nu-Calgon-416...ay&sr=8-3&th=1
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Old 06-19-2019, 07:59 PM   #10
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Quote:
Originally Posted by powerboatr View Post
let me add.
these puppies are just not designed for occupant comfort at or near 100F outside, shamefully.
we also CLEAN the a/c condensor coils routinely with coil solution , spray on and let it run down and rinse with fresh water, it does wonders

nu calgon makes a great product its on amazon
All current Tuscany's come with three, 15,000 btu Coleman Mach 8 A/Cs. I find than traveling in south Texas in July, the single 15,000 btu Mach 15 and the dash air keep the coach at 80 degrees in the rear and 75 degrees up front. Parked in the San Antonio sun, the two roof top A/C keep the coach at 75 degrees if the Magne Shade is installed.
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Old 06-19-2019, 08:33 PM   #11
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Quote:
Originally Posted by MJC62 View Post
My neighbor the a/c guy says best way to gauge the A/C performance take the temp at the outlet nearest the unit. A well functioning unit should be kicking out around 25* or more below the outside ambient temperature. So far this summer we have not gotten anything over mid 80*'s in NW Indiana. Our 15000 btu unit has been consistently 53* at the nearest outlet to the unit. BSexton hit the nail on the head get the unit cold and keep it that way.
Comparing outlet temperature to outside ambient temperature can be misleading because the outlet temperature is also a function of how much cooling capacity you have compared to requirement, not just whether the A/C is working correctly.

The normal way to get a quick read on performance is to compare outlet temperature to the return temperature, which is essentially the temperature inside the RV. So a 55 F outlet temperature in an RV that is 80 F gives 25 F cooling, even if outside is 95 F.



For what itís worth, 95 F outside ambient is standard temperature for A/C capacity rating, but these rooftop units are also rated to cool in desert conditions which are much hotter outside. If one installs enough cooling capacity, the motorhome will cool down even on a 100 F day while parked in the sun. Itís just too expensive to mass produce motorhomes with that much cooling when very few will need that extreme, and rarely at that.
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Old 06-19-2019, 09:35 PM   #12
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Quote:
Originally Posted by Beau388 View Post
All current Tuscany's come with three, 15,000 btu Coleman Mach 8 A/Cs. I find than traveling in south Texas in July, the single 15,000 btu Mach 15 and the dash air keep the coach at 80 degrees in the rear and 75 degrees up front. Parked in the San Antonio sun, the two roof top A/C keep the coach at 75 degrees if the Magne Shade is installed.

mine is an 08 and it only came with two 13.500 btu units
we replaced them a few years ago with 15k btu heat pump units.

i have been toying with adding one more unit for the kitchen area.

40 feet with 6 slides in the heat of the day 100f its a journey to keep the bus cool to 78, but i like at 76F.

If we are parked tail to the west, its easy. but the nose into the west sky and its a challenge
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Old 06-19-2019, 10:34 PM   #13
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They are correct .... The best thing you can do is "heat management".

Dont let the inside get above 80 deg if you can help it. Takes a long time to suck the heat out of the furniture and inside walls (esp if in full sun).

Use the refective bubble in all the windows that you can.... esp the side that is facing the sun.

I had "clear" (Well 15% so almost clear) ceramic window tint installled on ALL my windows (the factory tint is just color.... no UV rejection - so this ceramic is a awesome). This helped greatly and we are not sitting in the dark with the windows covered with reflective bubbles all the time.

Check your return air duct inside the AC unit. Mine was sucking hot air on the cold side (do a search on this - lots of threads on this subject). Plus I insulated the AC unit on the roof (plus AC lines) and moved my Thermister probe up about two inches.

I went from 65 deg output temp (at ac dump vents and roof vents) to 45 deg!!! It blows that temp no matter what the outside temp is. So I can get in the mid to low 70's (95 deg outside) and even high 60's if its only like 88 deg (or less) outside!!

So reject heat first then make your exsisting AC unit work better before you add any more AC units. You might be pleased like I was (but My RV is only 27 foot so one AC works fine for me).
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Old 06-19-2019, 11:27 PM   #14
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THOR #1808
great advice on sealing up the cold air leaks into the hot side.
all my ceiling vents were removed and i taped the inside edges with alum duct work tape, the edges were raw and air was blowing through the attic??
i also put in dampers, if you will in the ducting so we have tow real zones, the rear a/c cools the bedroom and bath and one vent in kitchen
the front cools the rest. this blocking off the ductwork produced higher velocity airflow vice the moth velocity prior to if only one a/c was running


we also double wrapped the cold box side of the rood a/c unit to keep heat loss at min.
all roof vents are wrapped with foil bubble insulation,

the skylight in shower inside trim was pulled out and covered with a fabric to stop the intense light, and then the cover was put back in.
and WEEKLY air filter cleaning
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Old 06-20-2019, 01:32 AM   #15
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Good Sam just posted an article on their blog on how to optimize the performance of an RV air-conditioner. They cover all the relevant points and even brought up a something I hadn't known about, which is the load on campground electrical grid can also reduce your systems efficiency under high demand.

Boost your RV's AC cooling power by following a few simple tips.
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Old 06-21-2019, 05:23 PM   #16
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Try getting the ceramic window shades put on your windows. That will help alit. Know that at best you will see about a 20 degree diff between inside and outside temps. These units arent like home systems. Shade and venting the hot air inside before you turn the system on is about all you can do...
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Old 06-22-2019, 01:14 AM   #17
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THOR #2757
Quote:
Originally Posted by Exilenla View Post
Fairly new to this whole Rvín thing... and our Miramar has two A/C units one in the main coach area, and one in the rear sleeping area.

We had it out in AZ again at the weekend 100F+ outdoors and the units were in full blast but the inside temp never got below the high 80ís ��

Does that sound normal???

Worth noting the unit in the rear did manage to cool the rear bedroom
Area to a comfortable temp.

Surely these units should get the coach down into the 70ís.... ����*♂️

Input / thought would be greatly appreciated
That sounds about right...most A/C roof units cool the air 20 degrees down...100-80, 80-60, etc!!! Hang in there, it's going to be a long hot summer!!

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Old 06-22-2019, 01:19 AM   #18
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THOR #2757
Quote:
Originally Posted by Long & Winding road View Post
They are correct .... The best thing you can do is "heat management".

Dont let the inside get above 80 deg if you can help it. Takes a long time to suck the heat out of the furniture and inside walls (esp if in full sun).

Use the refective bubble in all the windows that you can.... esp the side that is facing the sun.

I had "clear" (Well 15% so almost clear) ceramic window tint installled on ALL my windows (the factory tint is just color.... no UV rejection - so this ceramic is a awesome). This helped greatly and we are not sitting in the dark with the windows covered with reflective bubbles all the time.

Check your return air duct inside the AC unit. Mine was sucking hot air on the cold side (do a search on this - lots of threads on this subject). Plus I insulated the AC unit on the roof (plus AC lines) and moved my Thermister probe up about two inches.

I went from 65 deg output temp (at ac dump vents and roof vents) to 45 deg!!! It blows that temp no matter what the outside temp is. So I can get in the mid to low 70's (95 deg outside) and even high 60's if its only like 88 deg (or less) outside!!

So reject heat first then make your exsisting AC unit work better before you add any more AC units. You might be pleased like I was (but My RV is only 27 foot so one AC works fine for me).

An example of what you can do to manage the hot air!!!
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Old 06-22-2019, 07:00 PM   #19
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THOR #13937
These are all great replies and I’m working. My way through all of them to compare our current set up. One thing I’m trying to do right away is get the actual circular vents off to see if the duct work is leaking. Some of the vents are hardly blowing (compared to others). I didn’t want to just force them off - is there a knack to it?

Thanks ����
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Old 06-22-2019, 07:09 PM   #20
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Originally Posted by DinoC41 View Post
That sounds about right...most A/C roof units cool the air 20 degrees down...100-80, 80-60, etc!!! Hang in there, it's going to be a long hot summer!!

Thanks 👍🏻
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