A/C question

rrjernigan · 06-18-2017, 03:59 AM

Got a 2017 Montana purchased in February and we spend most of our time in Texas. It is now getting hot. Trailer has two A/C units. Rear area gets warm while the front bedroom stays cool. We basically face the south so sun passes over the passenger side where all the windows are. We do keep the shades closed to help a bit. Not a great deal of shade in our spot. Rear A/C is putting out cool/cold air (going to take it's temperature later today).

Thinking of possible solutions. We can add a third A/C unit in the Kitchen area that would not be duct'ed. We can purchase sun screen reflectors (the silver things we see in other units) and attach them to the windows, especially the rear.

Any thoughts?

thanks.

PARAPTOR · 06-18-2017, 04:58 AM

We have had many threads/posts on this topic. Many members asking the same questions. I highly suggest doing a search on say AC. Since you have ducted AC, I assume you are adjusting the registers, checked the tape on all interfaces, and again tried things recommended in previous posts.

In these previous posts you will find a post by John addressing expectations of a RV AC. You mentioned possibly adding another AC, you need to read previous posts on pro/con of adding that third AC.

Are you using any other fan(s) to move this cooled air.

**JRTJH** · 06-18-2017, 07:22 AM

The most significant problem I've found with ineffective "dual air systems" is leaks in the ducting. The "attic space" on Montana's is vented, so there is "free air flow" in the attic around the ductwork. It seems like a good way to control moisture, but it wreaks havoc on trying to contain and minimize a small air leak in the foam A/C ducting. Any leak of "precious" (not using the term loosely, every bit of cold air is important in an RV) conditioned air that flows into the attic is lost cooling capacity.

As soon as most RV's are towed from the factory to the dealer, the roof structure, sidewalls and even the floor will flex and pull away some of the "great craftsmanship" that comes from the factory. So, fully expect that you have leaks in the ducting, leaks in the plenum and leaks especially at the vent outlets (which are press fitted) into the ceiling mounted vents.

Use some aluminum duct tape, spend an afternoon sealing and rechecking all the vents and the "divider board" in the cold air/return air plenum. You'll probably find a significant improvement in "air pressure" from the vents and a few degrees of improved comfort.

Shade (avoiding direct sunlight) is the biggest factor in keeping a poorly insulated RV cool. Any sunlight that shines into the RV will heat inner surfaces. We have "sun block screens" that I bought at Home Depot that I cut to fit the large windows. I hold them in place using self stick Velcro tabs in the corners of the window frame and the screen. Total cost about $30 and well worth the effort and investment.

For most RV's, plan on getting tired of the A/C noise as it runs 24/7 on a hot day and still doesn't match the comfort of the S&B house.... Just the nature of the beast. I know people with 45' "million dollar motorhomes" with 4 rooftop A/C units and they also complain of "it's hot in here" when their black motorhome with the gold and silver "swooshes" is parked in the open at Sam's Town in Las Vegas.....

rrjernigan · 06-18-2017, 08:28 AM

Quote:

Originally Posted by JRTJH

The most significant problem I've found with ineffective "dual air systems" is leaks in the ducting. The "attic space" on Montana's is vented, so there is "free air flow" in the attic around the ductwork. It seems like a good way to control moisture, but it wreaks havoc on trying to contain and minimize a small air leak in the foam A/C ducting. Any leak of "precious" (not using the term loosely, every bit of cold air is important in an RV) conditioned air that flows into the attic is lost cooling capacity.

As soon as most RV's are towed from the factory to the dealer, the roof structure, sidewalls and even the floor will flex and pull away some of the "great craftsmanship" that comes from the factory. So, fully expect that you have leaks in the ducting, leaks in the plenum and leaks especially at the vent outlets (which are press fitted) into the ceiling mounted vents.

Use some aluminum duct tape, spend an afternoon sealing and rechecking all the vents and the "divider board" in the cold air/return air plenum. You'll probably find a significant improvement in "air pressure" from the vents and a few degrees of improved comfort.

Thanks. I know nothing about ac systems. What is the divider board and air plenum? I've read a bit about them but do not know where to look for them nor what to look for.

PARAPTOR · 06-18-2017, 11:36 AM

That divider can be accessed from the inside by removing the cover from the unit. As stated if you search say for AC there are pictures of this area in the many posts

**JRTJH** · 06-18-2017, 05:12 PM

I was thinking about this problem on the way back from a graduation open house this evening. If I remember, the Montana has the "quiet cool" A/C system. What that means, I believe, is that the return air is from vents located along the sides of the ceiling and ducted back to the plenum. If so, any leak in that system would also "draw hot attic air" into the ductwork creating an additional "heat load" on the cooling unit.

So, along with looking for leaks in the "cold air delivery" also look for leaks in the "return warm air" parts of the Montana's "elegant A/C system"....

rrjernigan · 06-19-2017, 11:53 AM

Thanks again. You are correct about the Montana. Air return is from vents along the sides of the ceiling, which also means there is no access to the a/c unit from inside the trailer.

I assume to look for leaks I need to remove the vent covers on the return air vents and the cold air supply vents into the camper and just look for any separations?

I purchased a laser temp gauge to see what the supply air temp and the return air temp is. In the bedroom (where it is always cool) the supply air (from the a/c unit) is upper 40's and the return vents show in the 70's. In the living area there are four supply air and two return air vents. The two supply air in the middle of the unit show 56 degrees and the two in the rear (where the sun beats in the most) show 52 and 56. return air is 75 and 78. Out side temp today is 86. Yesterday it was mid 90's and the cold supply air in the rear was upper 60's with return mid to upper 80's.

My wife mentioned the metal on her window was very hot. It read 125 inside the camper. Today I purchased some of the silver reflective insulation and velcro and have installed it. I'm not allowed to get on a ladder or stretch to remove the vents just yet (still recovering from hernia surgery) so I have to wait to check for gaps.

As a side note, you cannot search on "ac" or "air". Those are too short so the search feature ignores them. I did scan on cooling and found lots of information.

And yes, we have fans going and an evaporative cooler (which doesn't help much).

Thanks again, I will keep you posted on progress.

dcg9381 · 06-20-2017, 11:34 AM

Quote:

Originally Posted by rrjernigan

I assume to look for leaks I need to remove the vent covers on the return air vents and the cold air supply vents into the camper and just look for any separations?

Yes. I found a bunch of leaks on our Carbon - the AC tape at the duct exits had come lose and was misdirecting cold air into the ceiling.. And creating a bunch of noise.

I have't tried it, but there are FLIR camera accessories for cell phones that might be very useful in spotting leaks.

rrjernigan · 06-20-2017, 01:53 PM

I will check those vents perhaps this weekend. So far the reflective material has made a huge difference and I haven't installed it on all the offending windows yet. We do lose the ability to look out while this is installed, but that is a small price to pay to be comfortable. We still have plenty of windows to look out.

**JRTJH** · 06-20-2017, 02:16 PM

We don't like to feel like we're "shut up in a box", so we've been reluctant to use the aluminum backed "bubble wrap" on our windows. We have used it in the past but didn't like the "closed in feeling"....

So, during our last trip to the "hot areas" I bought some "solar blocking screen" from Home Depot. At that time, all they had was charcoal color. I cut the screen (it comes in rolls) to fit the outside frame of the large windows. I used "industrial strength" adhesive Velcro in 2" tabs taped to the window frames (stiff side of the Velcro on the frame/soft side on the screen material). When we get to a campsite and it's located so the big windows will be exposed to the sun, I just unfold those screens and put them on the outside of the windows. It blocks the sun and we can still see out, actually better than without them because it stops the glare.

I just looked at Home Depot's website for the solar screen and I found that they now have some lighter colors, some that I think would actually work better than the dark charcoal we have... Hmmmm I may be making a trip to HD before long..... Anyway, here's a link to one of the kinds of "light stucco" colored "sun block screen".... You might also find it interesting as an alternative to the bubble wrap insulation that blocks your view.

http://www.homedepot.com/p/Phifer-48...tore/202176184

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