I guess there are two ways to keep your motor home cool when going down the highway. Run the dash air. Run the generator and overhead air. What is the good, the bad,and the ugly about running your dash air only. Is the dash air alone able to cool the motor home? Does it lower the gas mileage significantly? Does it lower the power of the engine?
Every coach will be different. You will have to experiment for yourself. Dash air if it will keep you cool will be more fuel efficient than running the generator. Use whatever it takes to keep you comfortable. When it is hot we use both.
If it's really hot, the dash air just can't keep up wioth the volume that needs to be cooled. The dash air doesn't effect gas mileage significantly. However, when it's real hot and the dash air can't keep up, I'll start the generator and run one of the roof/house AC's. This will keep us and the dogs comforable, and it uses about a gallon of gas an hour, IIRC. For us, getting about 7 MPG to start with, it doesn't make much difference. We've got to stop for fuel every so often anyway, and we like to be somewhat comfortable. It's all realitive !
Joyce '46 (DW)
GOOD SAM LIFE MEMBERS
Heidie '00 (#1 Guard Dog, 11 lbs) & Reggie (#2 Guard Dog in training, 11 lbs)
'05 Winnebago Voyage 35A, Workhorse W22
'03 Cavalier Toad w/Sterling Aluminum Tow Bar & Brake Buddy
When I first up the MH, I kick on the overhead AC. As I travel down the road, I put the dash AC on and run them both until the MH has cooled down. I then cut off the overhead AC and only restart it if the dash AC cannot up with the demand.
We use the dash air and both roof units as necessary. And yes the dash air does affect fuel economy, not percentage wise as much on your motorhome as it would on your Toyota Yaris but it definitely does.....
OEM Auto Engineer 2003 Damon Challenger 348 Class A - F53 Triton V10
2006 Jeep Grand Cherokee Limited 4x4 V8 Toad
We have found that the dash A/C keeps our 24ft C "bearable", but just. And only when on the road. During summertime highs, if we are parked, the dash is certainly better than nothing, but not enough. We don't have an on board genny. If you are attempting to cool the coach from the dash, it is important to keep the air moving. We leave the rear most roof vent cracked and it seems to draw the air back as we go down the road. Still experimenting with which A/C vents to have working; dash, feet, defrost, mix, etc. YMMV.
87 Mallard Sprinter 24' Class C Ford E350 w/460 gas "The Runny Duck"
Shiny side up, Rubber side down.
This is very dependent on the size of your motorhome. There is no problem running the overhead/coach A/C while driving with your generator on - in fact, the on-board generator has to be used at least once a month under load for a few hours to keep it in good running condition so riding with the generator on and the coach A/C running is a good thing. In our little Class B, the dashboard A/C is plenty, but if you have a large Class C or Class A then using the generator and A/C to get down to temperature and having the dash A/C on at the same time is the way to go - but it is your choice depending upon what the size of your coach needs.