Engine A/C vs. House A/C

Never thought of opening a window or using the defroster.

We just started using the rooftop AC while traveling. It only cools the coach 5 degrees but the difference between 95 and 90 is noticeable.

Hi Joe jmccen58,

Given your rig is a very large 31 footer, I would think the dash a/c alone would not be effective throughout the coach on hotter days, not so good a situation when people are in back while traveling. If that is your case, then you pretty much have to run the generator. At least you would also benefit from 110v operations.

Our shorter rig with less interior volume, lower ceiling, closer side walls, good insulation, thermal windows, and no slide outs, the dash a/c is very effective in back, as is the heater.

I don't have hard numbers, but running a 4000 Onan generator will use more fuel than the chassis a/c while driving . If parked and idling, running the generator versus idling the Ford-V10 chassis engine, I would think a 4000 Onan generator will be the more efficient choice.

Not everyone can ignore vacation costs. It's a good question to ask.

Desert Captain wrote:
The dash AC in our 24' C (E-350), is more than capable of cooling the entire coach so I've never even considered running the genny to get more cooling from the roof AC(just another benefit of having a 24' coach). The V-10 has plenty of power and we never hesitate to run the AC and I can discern no appreciable difference in mileage with it on or off.

The same here regarding our 24' C.

That's one reason we wanted a small Class C. We figured the heating and cooling appliances would offer more over-kill so as to ensure comfort under a larger variety of planned or un-planned camping situations.

We have use both air conditioners once for a fast cool-down during lunch after rock-hounding ... in the desert of the Texas panhandle during August.

The dash A/C usually is sufficient until it gets above 85 degrees outside, then both go on. We have a pocket door between the bedrooms and rest of the motorhome, so we close all vents in the bedrooms and bathroom and close the pocket door so we only cool the front half of the motorhome. The Roof Top A/C can't cool the cab area, so the dash A/C is always on.

-Michael

My van has factory dual A/C (front and rear). I cannot tell any appreciable difference in fuel economy even when both are cranked. I can however feel when the engine fan kicks in, so occasionally I'll turn off the A/C to keep the fan down while climbing.

When underway I'm more interested in keeping cab comfortable than the coach. The cab AC is where I need it. It frequently can be run in recirc (max) mode at low fan speed. Compressor is cycling on and off-and I would think fuel consumption penalty is minimal. Cab is cool, coach is cooler than outside.

Big difference in windshield heating between an A and C.

Our truck AC Cools the complete inside of the MH if we keep a vent in the rear bath open some. It pulles the cool air thru and its nice inside even at temps over 110 degrees F. as long as we are moving. The roof AC is ducted and does fair but not much for the cab area so cab becomes hot. Cab AC does so good we find no reason to run both. As far as fuel difference by running one or the other I really have found little difference. For our rig using the cab AC while traveling gives us far more comfort but really may cost us 20 or 30 cents per hour more.

No real difference in gas mileage for me. I run both when needed to stay comfortable.

Dash A/Cs are a lot more powerful than rooftop A/Cs, because they have to cool off a fairly large air volume almost instantly.

If I need to get a MH cool, I run both A/Cs. If I want to keep it cool, just the top A/C. Supposedly some people have luck in opening a rear window a bit so air from the dash circulates from front to back. Doesn't sound intuitive, but apparently that gets the hot air out of the rig, but I have yet to try that.