View/Navion & Staying Cool

[usmcshepherd]

Hello,

It’s been a while since I posted on RV.net but we are considering a new rig and am starting to do some research. One of our biggest questions / concerns since we now live in the desert SW is whether the onboard A/C (run by generator) is powerful enough to keep the coach cool when going down the road in 100+ degrees?

Thanks
Tim

[JaxDad]

Rick Jay wrote:

JaxDad wrote:
That’s why so many people incorrectly believe the rooftop unit is more powerful when in reality (in the case of a Ford C chassis) it’s barely a quarter the capacity of the Ford unit in the dash.

Just curious, do you have any numbers/examples to back that up? Most of the vehicle chassis A/C's I've worked on (cars mostly) are rated 15k-20k BTU's. RV roof A/Cs are typically 13.5k-15k BTU. When you say "...barely a quarter..." suggests that there are 50k-60k BTU (4 - 5 Tons of cooling!) A/C compressor units under the hood. I don't believe that to be the case for the majority of vehicles. It might be the case for transit buses and such special purpose vehicles, but not the average vehicle chassis.

~Rick

You are correct, most cars do have a 15k to 20k unit, but in larger vehicles like full size SUV’s and passenger vans they instal much larger capacity systems.

According to the service manual for my unit the system takes 68 ounces of refrigerant, that’s 4.25 pounds. If you do the math that works out to more than 60k of cooling capacity.

I can’t find the link at the moment but I had found one that said a Sprinter chassis had a theoretical capacity of about 50k which makes sense because for passenger use you can add a rear auxiliary a/c unit of 30k to the existing system, it does not require a second compressor.

[Rick_Jay]

usmcshepherd,

I think probably the best way to answer your question is to test drive a couple of units and make your own decisions. I think there is possibly a more complex answer than one would initially think.

People have different ideas as to what is comfortable. I know a few people who absolutely HATE A/C. Me? I like it nice and cold! LOL So what is comfortable for some on the forum might not be for you and your passengers.

There are several variables that can come into play, as well. How many people will be travelling? Do you have any pets? People and pets both add to the heat load of the A/C system.

Are the windows insulating dual-pane glass? Does the rig have a dark, full-body paint job?

Now, all that being said, you're looking at relatively small RV's so I would optimistically expect a reputable manufacturer to install the proper equipment to maintain a comfortable level inside the motorhome while travelling. However, we are talking about the RV industry, here, and "optimistic expectations" are probably not worth much.

One other thing to consider, though, is if you have a diesel engine, and a propane generator which you will be using to help maintain the comfort level, you'll probably be refilling the propane tank fairly frequently. While a more expensive alternative, if you have the option for a diesel generator, there is a lot of convenience having the generator fuel being the same as the chassis engine fuel.

I haven't done much research on these types of vehicles. I've looked at them at shows and such and browsed websites, but that's about it.

I think a couple of test drives in various units will best answer your questions to your satisfaction. Just try to arrange them on a hot, sunny day! LOL

Good luck in your search,

~Rick

[Rick_Jay]

JaxDad wrote:
That’s why so many people incorrectly believe the rooftop unit is more powerful when in reality (in the case of a Ford C chassis) it’s barely a quarter the capacity of the Ford unit in the dash.

Just curious, do you have any numbers/examples to back that up? Most of the vehicle chassis A/C's I've worked on (cars mostly) are rated 15k-20k BTU's. RV roof A/Cs are typically 13.5k-15k BTU. When you say "...barely a quarter..." suggests that there are 50k-60k BTU (4 - 5 Tons of cooling!) A/C compressor units under the hood. I don't believe that to be the case for the majority of vehicles. It might be the case for transit buses and such special purpose vehicles, but not the average vehicle chassis.

As far as opening a vent in the back of the rig, if that works for your rig, more power to you. There are some rigs, ours happens to be one of them, that with a window or vent open while travelling, creates a slight negative pressure in the vehicle. Under the right driving conditions (curvy & hilly roads usually) the sloshing around causes some of the water in the sink p-traps to slosh into the holding tank and the slight negative pressure then draws up the gray tank odors into the RV. NOT pleasant!!! LOL So, we travel with windows & vents closed and sink drains plugged. 🙂

If there is a recirculate button on the A/C control, than that will generally allow the maximum cooling in the RV once the interior of the RV is LESS THAN the outside temperature. Those A/C controls that don't have a recirculate option specifically stated (such as our RV dash A/C control panel), often accomplish the same task when the selector is placed in the "Max" position, closing the duct(s) bringing in outside air and recirculating the cabin air.

~Rick

[pnichols]

But of course that cab air filter has to be changed periodically ($) if one makes use of it all the time, and ... of course it allows hot outside air through it that must be cooled all the way down by the cab A/C sytem.

We just think that is makes more sense to use recirculate at all times for better control of the interior air environment.

[JaxDad]

Must be a local thing in your area. I do probably on a yearly average. 2 trips a month, some long, some short. I’ve never noticed any more dust in my RV than my house, and I live in farm country.

Ditto my car, mind you nearly every automobile made in the last decade has a cabin air filter so that’s not much of a comparison either.

[pnichols]

JaxDad wrote:
So you run your dash unit on recirculate all year-round, regardless of the temperature?

Yes .... pretty much.

This both keeps the coach interior cleaner, and eliminates odors and fumes coming in from the outside air.

That's also how we mostly run the systems in our pickup truck and daily driver sedan. Out home's heat pump system also only recirculates the air in both it's heating and cooling modes. Of course our RV's rooftop air conditioner also only recirculates the interior air, too.

[JaxDad]

Expyinflight wrote:
We live in the Arizona desert, and travel frequently in 100+/- degree temps. We like it cool and comfortable. We run both the chassis air and the generator/roof top air...every time. The generator usually needs some exercise anyway. And no...I don't care how much gas it uses.

The actual temp here was 97 deg. F here last weekend, about 112 deg. f with the humidex factored in.

I used my method because I needed maximum cooling not just that little rooftop unit.

[JaxDad]

pnichols wrote:

JaxDad wrote:
Opening the rearmost roof vent completely and leaving the dash A/C on normal has been (informally) proven to be the most effective by far.

That introduces dust and dirt throughout the interior due to the constant flow of outside air from front to back within the RV.

We'd much rather keep everything closed up, use the cab A/C on recirculate to maximize use of the cab air conditioner's tremendous BTU capacity, and then move air around to the back of the coach area while traveling using one or two of these incredible 12 volt fans:
https://www.amazon.com/Fan-Tastic-Vent-01100WH-Endless-Breeze/dp/B0000AY2Z6/ref=lp_2591693011_1_1?sr...

So you run your dash unit on recirculate all year-round, regardless of the temperature?

[pnichols]

JaxDad wrote:
Opening the rearmost roof vent completely and leaving the dash A/C on normal has been (informally) proven to be the most effective by far.

That introduces dust and dirt throughout the interior due to the constant flow of outside air from front to back within the RV.

We'd much rather keep everything closed up, use the cab A/C on recirculate to maximize use of the cab air conditioner's tremendous BTU capacity, and then move air around to the back of the coach area while traveling using one or two of these incredible 12 volt fans:
https://www.amazon.com/Fan-Tastic-Vent-01100WH-Endless-Breeze/dp/B0000AY2Z6/ref=lp_2591693011_1_1?sr...

[Expyinflight]

We live in the Arizona desert, and travel frequently in 100+/- degree temps. We like it cool and comfortable. We run both the chassis air and the generator/roof top air...every time. The generator usually needs some exercise anyway. And no...I don't care how much gas it uses.

[JaxDad]

pnichols wrote:
Regarding use of the cab A/C system - whether it be a Sprinter, Ford, Chevy based chassis - it's most effective if you don't expect the cab A/C system to keep cooling fresh incoming hot air from the outside.

Set the cab A/C system to it's recirculate mode so that the system is merely adding cooling to already-cooled interior air.

In numerous tests me and a bunch of others have proven this is not the most effective way to do it.

The fan in the dash A/C system is by FAR the weakest part of the system.

That’s why so many people incorrectly believe the rooftop unit is more powerful when in reality (in the case of a Ford C chassis) it’s barely a quarter the capacity of the Ford unit in the dash.

You need to move air, and LOTS of it.

Opening the rearmost roof vent completely and leaving the dash A/C on normal has been (informally) proven to be the most effective by far.

[CharlesinGA]

pnichols wrote:
Regarding use of the cab A/C system - whether it be a Sprinter, Ford, Chevy based chassis - it's most effective if you don't expect the cab A/C system to keep cooling fresh incoming hot air from the outside.

Set the cab A/C system to it's recirculate mode so that the system is merely adding cooling to already-cooled interior air. Make sure to have all windows and vents closed to maximize this process. Don't worry about feeling weak from the interior oxygen getting low ... when going down the road there's plenty enough leaks even with all windows/vents closed to supply what our lungs require.

We travel this way in hot weather all the time and rarely has our Ford E450's cab A/C system had to be set to it's highest cooling setting or fan speed setting to keep the coach comfortable from the cab on back. The recirculate mode for our E450's cab A/C system is labeled as "Max A/C".

P.S. When traveling this way you also keep the coach interior nearly free of outside airborn dust/dirt, keep the interior air nearly free of other vehicles' exhaust fumes, and keep the interior air nearly free of slaughter yard/etc. smells. 😉

I agree with you completely, why waste energy cooling outside air when you can more effectively use energy re-cooling the inside air that is already somewhat cool.

A Sprinter has one quirk that I am left wondering what MB was thinking when they did it....... The recirculate mode will only stay on for 15 minutes and then it will switch back to outside air. Every 15 minutes when you notice the A/C barely working again, you reach over and hit the recirculate button again.

On my Sprinter chassis one of the plastic cranks in the recirculate door linkage is broken, and irreplaceable, and I have permanently secured the door in the recirculate position. If I want outside air, I open a window.

Charles

[suprz]

Rooftop a/c is only good normally for a 20 degree temp difference. Due to the outside factors of rv's. ( poor insulation etc...)

[JumboJet]

Just finished a trip with our 31' on an E-450 chassis Arkansas to California through New Mexico, Arizona, Needles, CA. Temperatures were near 110 in Needles. Dash Air worked great until Sun started coming in non-tinted windows. Fired up generator and ducted house air. Cab and living area stayed reasonably cool. Rear bedroom - a heat sink. Oscillating fan running trying to pump cool air into the bedroom helped.

When we got home, I purchased a Coleman Mach 8 9.2k BTU AC and added to the bedroom. A world of difference in cool down time. I prefer to sleep cool.

Smaller RVs probably do not need two AC units.