Go Back   iRV2 Forums > MOTORHOME FORUMS > Class A Motorhome Discussions
Click Here to Login
Join iRV2 Today

Mission Statement: Supporting thoughtful exchange of knowledge, values and experience among RV enthusiasts.
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on iRV2
Thread Tools Search this Thread Display Modes
Old 07-23-2009, 04:31 PM   #1
Senior Member
Join Date: Jul 2008
Posts: 127
Southwest US A/C Use

Been full timing about a year on the East coast and have used the A/C from PA to FL and understand the the A/C concept. We have vacationed in the Southwest yearly since 1999, but this will be our first visit 9/09-4/10 out west. Since it is a DRY heat how does the A/C actually work since there is virtually NO moisture to extract. Normally it is 7-1% depending on where you are at. Thanks in advance for your replies. Coach is 2008 Winnebago Voyage with basement air.


navyblue is offline   Reply With Quote
Join the #1 RV Forum Today - It's Totally Free!

iRV2.com RV Community - Are you about to start a new improvement on your RV or need some help with some maintenance? Do you need advice on what products to buy? Or maybe you can give others some advice? No matter where you fit in you'll find that iRV2 is a great community to join. Best of all it's totally FREE!

You are currently viewing our boards as a guest so you have limited access to our community. Please take the time to register and you will gain a lot of great new features including; the ability to participate in discussions, network with other RV owners, see fewer ads, upload photographs, create an RV blog, send private messages and so much, much more!

Old 07-23-2009, 05:43 PM   #2
Senior Member
Jim Stewart's Avatar
Monaco Owners Club
Join Date: Nov 2008
Location: Melbourne & Marathon, Florida
Posts: 1,537
Here is an explanation for you, sorry for the length.

Air conditioners use chemicals that convert from a gas to a liquid and back again. This chemical is used to transfer heat from the air inside of the motor home to the outside air. The machine has three main parts. They are a compressor, a condenser and an evaporator.

The working fluid arrives at the compressor as a cool, low-pressure gas. The compressor squeezes the fluid. This packs the molecule of the fluid closer together. The closer the molecules are together, the higher its energy and its temperature. The working fluid leaves the compressor as a hot, high pressure gas and flows into the condenser.

When the working fluid leaves the condenser, its temperature is much cooler and it has changed from a gas to a liquid under high pressure. The liquid goes into the evaporator the liquid's pressure drops, when it does it begins to evaporate into a gas.

As the liquid changes to gas and evaporates, it extracts heat from the air around it. The heat in the air is needed to separate the molecules of the fluid from a liquid to a gas. The evaporator also has metal fins to help in exchange the thermal energy with the surrounding air. By the time the working fluid leaves the evaporator, it is a cool, low pressure gas. It then returns to the compressor to begin its trip all over again.

Connected to the evaporator is a fan that circulates the air to blow across the evaporator fins. Hot air is lighter than cold air, so the hot air in the room rises to the top of a room. There is a vent there where air is sucked into the air conditioner and goes down ducts. The hot air is used to cool the gas in the evaporator. As the heat is removed from the air, the air is cooled. It is then blown into the motor home through the other ducts.

This continues over and over and over until the motor home reaches the temperature you want it cooled to. The thermostat senses that the temperature has reached the right setting and turns off the air conditioner. As the motor home warms up, the thermostat turns the air conditioner back on until the motor home reaches the temperature.

When you first turn on air conditioning and it is hot and humid, and the windows are open, there is a lot of moisture in the air. When you close the windows and turn on the air conditioning, the air conditioner will use about of its energy initially to remove that moisture from the air while it cools. Because there is more moisture in the air to remove at the start, the air conditioner will take longer to cool the motor home down, with only half of its energy going toward cooling. However, after the air conditioner runs for a few hours, the majority of the moisture will be removed. At this point, the air conditioner can cool much more quickly, as well as run for shorter times to maintain that cool temperature.

When in arid conditions, where there is less moisture, more energy is going toward cooling and that is a good thing, because generally the temperatures are higher. In many arid parts of the USA they actually use something called an Evaporative Cooler that adds moisture to the air. The Evaporative Cooler runs water across grids while a large fan blows across the grids. This addition of cool water blowing moisture into the air reduces the temperature.

There you go!


2005 Safari Cheetah 38PDQ - 2009 Ford Flex
Me (Gatogonow), The Boss (DW), Honey Bunny, Maggie May and Mollie Kay (The Gatos)!
Jim Stewart is offline   Reply With Quote
Old 07-23-2009, 06:20 PM   #3
Moderator Emeritus
Gary RVRoamer's Avatar

Join Date: Jan 2000
Location: Silver Springs, FL. USA
Posts: 18,635
The a/c works just fine in a "dry heat". The humidity - or lack thereof - has nothing to do with the efficiency of the a/c cycle that Jim described so thoroughly.

It does, however, affect your comfort by improving the efficiency of your body's cooling system, i.e. perspiration. Sweat evaporates quickly off your skin, helping you cool. You just have to keep drinking liquids to replace the water loss. That's why you feel more comfortable in a "dry heat" than a high humidity environment.
Gary Brinck
Former owner of 2004 American Tradition
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC
Gary RVRoamer is offline   Reply With Quote
Old 07-23-2009, 06:51 PM   #4
Senior Member
Join Date: Jul 2008
Posts: 127

Thanks both for your replies. Jim, although my degree is in Economics, I understood every word you said as I did very well in Chemistry in school. I just couldn't get the concept of AC working well in a low humidity scenario, but I can now see how it works. Gary, I became familiar with the "Swamp Cooler" concept from a DESERTUSA site I go to for desert info

navyblue is offline   Reply With Quote
Old 07-23-2009, 07:10 PM   #5
Moderator Emeritus
TXiceman's Avatar

Vintage RV Owners Club
Texas Boomers Club
Oklahoma Boomers Club
Ford Super Duty Owner
Join Date: Aug 2000
Location: Full Time, TX Home Base
Posts: 17,169
Blog Entries: 21
In the air conditioning process ther is two parts of the cooling...sensible, which is the cooling of the dry bulb temperature and latent cooling which is the lowering of the wet bulb temperature. In low humidity, the wet bulb (or the amount of moisture in the air) is much lower and you will very little if any condensation on the evaporator coil. You can actually have more problems with the evaporator icing in low humidity since the load ins much lower and the compressor will rebalance at a lower suction pressure and temperature which can be below freezing. So run the fan on high if you start to get icing problems.

It is actually more comfortable in a dry climate to use an evaporative cooler (swamp cooler) which will put some moisture back into the air and still drop the temperature way down, depending on just how low the wet bulb is to staty with.

An evaporative cooler is much less expensive to run than refrigerated air.

Been in the refrigeration and A/C business on large industrial systems since 1970.

Amateur Radio Operator (KE5DFR)|Full-Time! - 2012 6.7L Ford Crew Cab Dually -2013 HitchHiker Champagne 38RLRSB - Travel with one Standard Schnauzer and one small Timneh African Gray Parrot
TXiceman is offline   Reply With Quote
Old 07-24-2009, 02:51 AM   #6
Community Moderator
RV Wizard's Avatar

Country Coach Owners Club
Appalachian Campers
Gulf Streamers Club
Join Date: Mar 2000
Location: Chattanooga, Tn.
Posts: 12,062
When we stayed in Apache Junction a year, I changed one habit that we do back east here. That is I did not open and run the ceiling fans to vent the moisture out. I kept them closed and used that moisture to bump up the humidity level and stayed quite comfortable as the air conditioner would pull it back out and would run all day long when it got to 110 or more.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7
RV Wizard is offline   Reply With Quote
Old 07-24-2009, 06:50 AM   #7
Senior Member
Chickadee's Avatar
Newmar Owners Club
Join Date: Dec 2007
Posts: 2,027
Jim: OUTSTANDING tutorial on our A/C operation. Thanks. Steve
2014 Newmar 3103 BAYSTAR/Triton V10 w. Banks/05 Honda Element toad
Chickadee is offline   Reply With Quote
Old 07-24-2009, 08:19 AM   #8
Senior Member
wa8yxm's Avatar
Damon Owners Club
Workhorse Chassis Owner
Join Date: Mar 2009
Posts: 23,927
I will second that. an Air Conditioner, well technically an Air Conditioner is anything that changes, hopefully for the better, any condition of the air, (I recall advertisments for a dollar forty nine air conditioner, it was a plug in air freshner)

However in common use we mean air coolers.

They are heat pumps, pumping heat from INSIDE to OUTSIDE,, Just like a slightly different (Reversable) version is called a heat pump. and they work in dry climes as well as wet..

The removal of humidity (Moisture) is a side effect in fact.

NOW... If, like me, when in the Arizona desert you are running on battery power a kilowatt worth of heat pump is not going to be something you want running all night. (Quite hours, no genny)

And. again if you are like me, that dry air does a number on my nasal passages... I need a bit more moisture in the air.


SWAMP coolers,,,, Mine is a "Gator" brand, purchased from E-bay, This unit can put gallons of water into the air in my bedroom during the course of a day, as the water evaporates it cools the air giving me as much as 10 degrees or more of lower temp. plus the moisture is good for me.. Oh, power draw on cool: 56 Watts per the Kill-a-watt

The model I have is also a heater.. Only plug in 2,000 watt heater (They are not kidding, it really draws 2,000, well, 1999.5, watts, I measured it, give me another fraction of a volt and it would have been 2,000) I have ever seen. Takes a 20 amp line (Though it has a 15 amp plug)

Swamp coolers come in 2 flavors, this one is a portable so it humidifies the room (Good for me) the other kind exhausts moist air outside the "house" and uses a heat exchanger to cool the inside. both run on water and very little electricity.

Home is where I park it!
wa8yxm is offline   Reply With Quote

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Summer Ready Basement A/C Pubtym Winnebago Industries Owner's Forum 16 07-26-2010 02:28 PM
Kit Camper Projects - Project #7, Installing a Household A/C Unit RedneckExpress Vintage RV's 1 02-03-2008 08:18 PM
A Rather Odd A/C Problem ( a bit long) gasbag MH-General Discussions & Problems 7 10-16-2007 10:10 AM
"Summer Ready" Basement A/C Pubtym Winnebago Industries Owner's Forum 7 06-30-2007 08:43 AM
Dash A/C Repair - Need some sage advice chasfm11 MH-General Discussions & Problems 11 11-06-2005 01:18 PM

» Featured Campgrounds

Reviews provided by

Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 10:33 PM.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.