Air Conditioning: Roof vs. Engine

[woodlodge]

I was told by the dealer where I bought my motorhome from that it is more economical to run my roof air conditioners (heat pumps) while driving than to run the engine air conditioning. I have to run my generator to do this, which will also use fuel just like the engine air conditioning.

Any opinions which method is better? I plan on taking a trip out West this summer to Yellowstone National Park and wonder which option would be the most economical

[kmsavage1]

We usually use only the engine AC, but we do whatever is necessary to keep comfortable including adding the Gen and the Roof AC if necessary. We regularly do use the gen and Roof Airs for the last 45-60 minutes before arrival in a park so that the coach is fairly cool when we stop. We basically never run only the Gen/Roof Air conditioners. Just my plan.

[genenick]

I find that running the generator costs about 1/2 gallon per hour. In my wildest dreams I can't see the dash air using 1/2 gallon per hour to operate. I do know that when I measure my fuel mileage in winter vs. summer I do not have a boost in mileage >2/10 between the two normally when I do not run the dash air.

I do run my roof air in the summer when I have passengers (grandchildren) for their comfort and find it works well. Sometimes I do turn off the dash air and place an oscillating fan blowing cold air on me, however I do not notice an appreciable increase in fuel mileage.

Hope this helps you with your question.

Merry Christmas,

Gene

[wolfe10]

You actually have several factors at work here:

Can the dash/engine-driven A/C do an adequate job of cooling-- can it keep me comfortable?

Does the dash A/C condenser add heat load to the engine, or is it out of the air flow of the engine cooling system-- important IF the engine coolant temperature is rising above thermostatic control.

If the dash A/C can keep you comfortable, the added load of the engine driven compressor still uses less fuel than running a separate motor (the generator). But, if it will not keep you comfortable or adds enough to the heat load of the engine that the coolant temperature rises above thermostatic control, then turn on the generator/roof A/C's. Be sure to put the dash A/C on recirculate when using the roof A/C's so you are not drawing in hot air from outside.

Brett

[Guest Wayne77590]

As Brett stated, in the recirculate position the dash air will actually use the room air to circulate the air through the dash. Some dash AC's cannot keep up with the demand in the hot Southern Summers. If you stick a thermometer in the dash vent you may notice an increase in temperature in the Summer time. Turning on the house AC and using recirculate will bring it back down to 40-50 degree rather quickly.

Good luck.

[f233844]

Another factor to figure, is that most of us don't use our generators enough.

Most of the generator problems come from lack of use, not over work.

Calculate an expen$ive repair job into the equation and see just where that leads you.

[janandkathy]

We normally do not have a problem using the chassis a/c. When we stop to eat I turn on the gen and house a/c to keep the coach cool for our Golden Retiever.

[hermanmullins]

I was told by the dealer where I bought my motorhome from that it is more economical to run my roof air conditioners (heat pumps) while driving than to run the engine air conditioning. I have to run my generator to do this, which will also use fuel just like the engine air conditioning.

Any opinions which method is better? I plan on taking a trip out West this summer to Yellowstone National Park and wonder which option would be the most economical

Woodlodge,

Welcome to the forum.

Many folks use a curtain behind the driver when using the dash ac to keep cool. Of course if you have passengers you might need additional cooling (gen and roof ac). I feel that our comfort overrides the MPG.

You will love Yellowstone!!

[WildBill95]

I noticed that when I run my chassis air (Damon w/Ford chassis) the passenger carpet gets wet. The condenser is draining so I don't think it is due to it being plugged, though it does drain for a while after I stop. I also noticed that there was condensation on the hose leading to the vent so I wrapped fiberglass insulation around that. Any idea of what could be the cause? I've about resigned myself to running the generator and house air in the summer.

[wolfe10]

I noticed that when I run my chassis air (Damon w/Ford chassis) the passenger carpet gets wet. The condenser is draining so I don't think it is due to it being plugged, though it does drain for a while after I stop. I also noticed that there was condensation on the hose leading to the vent so I wrapped fiberglass insulation around that. Any idea of what could be the cause? I've about resigned myself to running the generator and house air in the summer.

Bill,

If the temperature of the outside of the condenser case is below the dew point of the air inside your coach, you will get condensation on the outside that will drip. Insulating it should solve your problem.

Also, running the dash air on recirculate should lower the humidity of the air inside the coach.

Brett

[jonrjen]

The way I look at it is, I purchased a motor home to travel the roads, see the country and be comfortable in my "Home on Wheels". If I were at home in my sticks-n-bricks house (actually it is styro foam/concrete/man made rock/metal roof) I set my A/C to keep the entire house cool. I don't shut off the vents in the rooms that I am not using. So in our motor home, if the weather requires running the generator to power the roof/basement A/C units while on the road in addition to the dash air I don't give it a second thought. In the scope of things, if it cost 1/2 gallon of fuel per hour to run the generator it is a cheap extravagance.

[marthabarnes]

I have been RVing since 1956 and have had many motorhomes. When I pull out of my backyard the generator is running, the A/C is on (if hot weather), the refig is on electric. If the weather is cold I don't run the a/c but that happens very seldom. When I traded my last motorhome (10 years old)I had 10,000 hours on my generator and everytime I took it in for oil change and check-ups they told me I would never have a problem with the generator because I used it properly. When parked in my backyard I go out every week, turn on the generator, start the a/c, and let it run for about an hour. I do my motorhome inside cleaning or just sit and watch TV. After 10 years with that generator I NEVER had a problem. Now I have another motorhome (4 years old) and the generator is going to be as good as the last one. Onan make a great product. I do run the engine A/C once a day when traveling for about 30 minutes then turn it off.

[danddferr]

I have been RVing since 1956 and have had many motorhomes. When I pull out of my backyard the generator is running, the A/C is on (if hot weather), the refig is on electric. If the weather is cold I don't run the a/c but that happens very seldom. When I traded my last motorhome (10 years old)I had 10,000 hours on my generator and everytime I took it in for oil change and check-ups they told me I would never have a problem with the generator because I used it properly. When parked in my backyard I go out every week, turn on the generator, start the a/c, and let it run for about an hour. I do my motorhome inside cleaning or just sit and watch TV. After 10 years with that generator I NEVER had a problem. Now I have another motorhome (4 years old) and the generator is going to be as good as the last one. Onan make a great product. I do run the engine A/C once a day when traveling for about 30 minutes then turn it off.

I agree, we don't use our gennys enough. I turn mine on just about every time I take the rig out. Since all of camping is done with hookups driving is the only time the genny is used. If I use it enough it will keep running right. Mine is a diesel and those puppies are made to run!

Dan

[lewisedge]

When I took delivery of my 2011 Itasca model 33C this past May 2012, my dealer also advised me to run the generator to power the roof air conditioners rather than use the engine/dashboard air conditioning. It was his contention that the extra load of the dashboard air conditioning on my Ford V10 engine would adversely affect my fuel mileage more than the 1/2 gallon per hour consumption by the generator. Taking my dealer at his word, I've not yet put that comparison to the test.

Have any of you owners of similar size rigs actually made that comparison? Some of the comments I've read in this forum suggest that running the engine/dashboard air conditioning has little adverse effect on mileage. Driving for a hour on a reasonably level interstate highway at a steady 60 mph, my rig will burn about 7.7 gallons of fuel. If my engine/dashboard air conditioning reduces my mileage by 0.5 mpg then the two would be a wash but the roof units would cool the entire coach. Additional comments on this subject would be appreciated.

[ClayL]

On mine DW had the return air intake to the dash AC blocked with some books. That caused the carpet and the books to get wet. The return air intake on mine is in the nook in front of the passengers feet.

[larrydyork]

I have an Itasca Suncruiser powered by WorkHorse. After four years of all season operation, I have just over 1000 hours on the generator. We always run the generator with basement air to keep the entire coach cool while driving in the summer. We also run the dash air to push a little more cool air in the cockpit area. I really can't detect any increase in fuel consumption running the dash air. I cannot detect any increase in engine temperature while we're moving. However, when we are stopped and there's no airflow over the condenser, I see a significant temperature rise in the dash air, and have to assume there is also an increase in engine temperature

In the winter, we use the coach heater, which heats the entire coach and basement, so there's really no need to run the heatpump. From summer to winter, I really don't see a significant difference in fuel consumption. I agree with others' comments; The coach is my hiway home, and my comfort is important.