I was at the RV show in Pomona CA this last weekend and was going through a new Tiffin Bus and the "sales" guy said that the AC units would lower the inside temp of the RV greater than the 20 degree rule.He said it would lower it like a house ac unit.So I called tiffin factory to see what they use and it is the Coleman Mach 15.So my question to all the RVers out there is:Do you have one of these on your RV ?If yes how much does it cool your RV from the outside temp, 20, 30 , 40, 50 degrees ?

Better add another qualifier: humidity.It takes a lot of BTU's to condense moisture.So, temperature delta in the desert WILL be different than along the coast.Are you in a dry or humid area?

I depends on the size of the RV, how well its insulated, how tight its built and what outdoor temp. its dealing with. A "sales guy" will tell you anything to make a sale. If its 75 degrees out side and and a unit can drop 30 degrees, that same unit would not do it at 95 0r 100 degrees ambiant.

A lot of people get confused over the "20 degree rule". They think that means it will only lower the temp in the rig that much. What it really means is the air that passes through the AC unit should cool about 20 degrees. But the same air passes through many times so it's plausible it could cool it much more than that amount - depending on heat load and humidity. Mine has pulled the temp down almost 30 degrees.

The temperature of the air coming off the coil should be about 35 -40 degrees. If it get any colder, and sometimes it does, it will freeze up form ice on the coil, I stick a dial thermometer in the duct where it comes into the motor home and I get about 40 -43 degrees.

Actually Tiffins, Winnebagos, and Berkshires are among the more poorly insulated units out there so it will take a heck of an A/C unit to cool them.I think the unit you are referring to is the one that Entegra is now using.

Coleman Mach 15 AC Unit | Good Sam Community

JCat
Explorer III
Oct 20, 2013
Thanks Doug for the firt hand experience with the ac units.

I am out in the desrt in Palm Springs and sometimes I stay here in the summer where temp reach 110 - 115 and no humidity.

Leaving all other items aside (insulation, humidity, etc) if my current units cool me down about 20 degrees, do you think the Mach units would do any better ?

I am trying to see if it would be worth doing an ac upgrade.

thanks
dougrainer
Nomad
Oct 19, 2013
JCat wrote:
I dont think I actually got an answer to my question from people who own a mach 8 or 15 ac unit
Anyone out there ?

The Mach 8 and a 15k are the same thing in BTU's. I do NOT own one but I work on Motorhomes in 100 degree heat and HAVE the Tiffin units running those AC units and we have them on the Sale lot WITH the Units running in 100 degree heat and they cool just fine. Doug
JCat
Explorer III
Oct 19, 2013
I dont think I actually got an answer to my question from people who own a mach 8 or 15 ac unit
Anyone out there ?
wnytaxman
Explorer
Oct 19, 2013
The sidewall insulation factors that I found were:

Winnebago 4
Tiffin, Fleetwood, Berkshire 7
Newmar 11
Entegra 16
J-Rooster
Explorer
Oct 19, 2013
wolfe10 wrote:
Better add another qualifier: humidity.

It takes a lot of BTU's to condense moisture.

So, temperature delta in the desert WILL be different than along the coast.

Are you in a dry or humid area?
X-2, I have a Coleman Mach unit in my Winnebago and have had troubles cooling down here in the Heart of the Mojave Desert. I expected my unit to really cool me down and that didn't happen! After investigating (from a air conditioning expert) it's all about humidity! At my summer home my unit runs really cool every year (80% humidity) down here in the Mojave Desert not as good (Humidity 8%). Brett is right on IMHO! I will add that my Coleman Mach unit might be obsolete since it's 10 years old? I've already found out that my engine and chassis are obsolete? Take Care, Rooster
Old-Biscuit
Explorer III
Oct 18, 2013
Coleman Mach 8
Pirate1
Explorer
Oct 18, 2013
dougrainer wrote:
I know what some will say---The salesman mouth was moving and he was lying. Well, sorry to say this is true, he may not be lying, but he has NO IDEA what he is talking about. The 20 degree "rule" is just an operational check for non technical people to verify if the AC is running and cooling to spec. That means the OUTPUT cold air will be 20 to 22 degrees LESS than the input air. HAS NOTHING TO DO WITH OUTSIDE AIR TEMP. It just means as the RV (or house) cools down the OUTPUT air will be 20 to 22 degrees colder than input---ie-- the inside of the RV is 90 degrees and the AC is started. After about 15 minutes the OUTPUT will be around 65 to 70 degrees and will get colder--after running the input air is now 80 degrees and the output is 60 or a little lower. The output will gradually get colder and colder as the RV cools down. The MAX output cold air will usually peak at about 40 to 48 degrees depending on humidity and the insulation of the RV and how hot the outside temps are. Home units operate about the same differential. The NEW Tiffins use the Mach 8 which is a brand new smaller physical size RVP (Coleman). Still has the same BTU's but is quieter and more efficient than the previous model RV models. Doug
Doug, I read the literature from MVP but their comparison chart didn't really show which was the Mach 15 and Mach 8. Do you have a comparison chart or link or something like that?
prism
Explorer
Oct 18, 2013
Actually I think(pretty sure) the entegra is the best insulated coach out there?
Anyone?
wnytaxman
Explorer
Oct 18, 2013
dougrainer wrote:
wnytaxman wrote:
Actually Tiffins, Winnebagos, and Berkshires are among the more poorly insulated units out there so it will take a heck of an A/C unit to cool them.

I think the unit you are referring to is the one that Entegra is now using.

Curious how you can state and know this? We sell and service Tiffin and they can freeze you out even in 105 degree temps. here in Texas we had 90 plus 100 degree days this summer and NONE of my Tiffin customers had a complaint about cooling their units. More amazing is you state the Berkshires have poor insulation, yet you are buying one????? AND you own a Winne now. NO OEM has a AC unit that only THEY can buy (Entegra). Doug

Doug, I'll see if I can find the R ratings on the different motorhomes. The listing is out there I just have to find it. Yes, I own a Berkshire and it is not particularly well insulated, but I don't live in a hot climate and we do not use our rig in the winter so it is not an issue for us.

The fact that a Tiffin's A/C units can cool the coach doesn't necessarily mean that the Tiffin's are well insulated. It only means that the A/C units are sufficient to cool the coach.

My comment about the Entegras did not imply that ONLY they were using the Coleman's. It was just stating that one particular manufacturer that is considered to be one of the better manufacturers uses that brand. It was meant only as an observation.
dougrainer
Nomad
Oct 18, 2013
wnytaxman wrote:
Actually Tiffins, Winnebagos, and Berkshires are among the more poorly insulated units out there so it will take a heck of an A/C unit to cool them.

I think the unit you are referring to is the one that Entegra is now using.

Curious how you can state and know this? We sell and service Tiffin and they can freeze you out even in 105 degree temps. here in Texas we had 90 plus 100 degree days this summer and NONE of my Tiffin customers had a complaint about cooling their units. More amazing is you state the Berkshires have poor insulation, yet you are buying one????? AND you own a Winne now. NO OEM has a AC unit that only THEY can buy (Entegra). Doug