Not only can you run your motorhome rooftop A/C while driving, you’ll probably want to in the peak months of summer. Class A motorhomes are huge and Class Cs are often pretty monstrous themselves.
Running the dash A/C against that size is like dropping a frozen penny in a pot of boiling water and expecting it to make a difference. Even with the A/C running, it can take up to two hours to cool a Class A from scratch in 90°+ weather. Imagine putting all of that on your dash A/C vents.
There are several good reasons for keeping your motorhome rooftop A/C on while driving. Traveling through Florida, south Texas, or Death Valley, California in the middle of the summer are just some of them.
Why Would You Run Both A/C Units At The Same Time?
You want to run both A/C (dash vents and rooftop unit or both rooftop units if you have two), for whole-home cooling. On a hot, sunny summer day, you’re dealing with several factors the A/C has to combat.
The greenhouse effect, even on small windows, takes a toll. Curtains (especially the blackout variety) help, but they are only part of the solution.
The generator is also its own worst enemy. Regardless of the power source, it heats up, and heat transfers through the bottom of the floor. Depending on the installation location of the built-in generator this can make a difference.
It’s worse if it’s coming through the floor because heat rises and it creates the same effect you get from an old-school radiator heater.
Laying down insulative blankets helps minimize this to a large degree. However, running all of your available A/C units keeps the entire rig cool and that’s the best solution for family members or pets in the back. It also preps the motorhome for arrival since it is already cool and ready to go.
Is The Motorhome Rooftop A/C Connected To The Dash A/C?
No. When you’re running the motorhome rooftop A/C while driving down the road, it’s operating under its own power (your generator). Your dash A/C is a separate, traditional setup with a compressor next to the vehicle engine.
In fact, regardless of the size of your motorhome, your dash A/C is basically the equivalent of what you get in a large SUV, 1/2-ton, or 3/4-ton truck. Your generator powers the rooftop A/C, however, there is a connection between the two. Your motorhome’s engine and the generator both pull from your gas tank in most rigs.
Sure, it tweaks your gas mileage in the negative a bit but it’s not like Class C and Class A motorhomes are world-renowned for their exceptional gas mileage in the first place.
Can I Run My Motorhome Rooftop A/C While Driving?
Yes, you can run your motorhome rooftop A/C while driving. In fact, you can run your RV furnace while driving as well. Summer can get pretty hot in the south. Now, imagine rolling through north Minnesota in February in Class A while only running the heater vents.
Family members and pets traveling with you will turn into popsicles in the back. So, it works both ways and that’s a good thing because the benefits outweigh the downsides, so long as you’re aware of both.
Gas or diesel-pusher motorhome generators consume roughly half a gallon per hour feeding the rooftop A/C. It’s important to calculate that into your overall trip. If you’re rocking a propane generator on your rig, you don’t have to worry about gas mileage but you do have to worry about state laws.
Some states regulate the use of propane power while you’re on the road. The safest bet is to always plan ahead and know the state laws before you cross state lines. It’s also a good idea to crank up the A/C about an hour before you hit the road.
Some motorhomes take longer to cool down but if you start the A/C before the birds start chirping, you won’t have to deal with the sun and the greenhouse effect. Insulative rugs, blackout curtains, and parking in the shade will help the motorhome cool off faster.
Is It Safe To Run A Motorhome Rooftop A/C While Driving?
It’s perfectly safe to run the motorhome rooftop A/C while driving. Since it runs on its own, separate system, it’s just as safe to run it while driving as it is to run it when you’re camping and not moving anywhere.
Propane generators are not unsafe but, again, it’s a good idea to check the state laws ahead of time, before you roll through. In some ways, it improves safety to run the A/C while driving. This is true when you’re tackling those mountainous roadways that feel like 80° inclines.
Running the dash A/C requires a compressor and every time that compressor kicks on, it robs the engine of power. If you’re running your rooftop A/C unit(s), you probably won’t need the dash A/C all that much. When it’s time to power up the side of a mountain, you can cut the dash A/C off and give your engine a little extra oomph.
Depending on the load limit of your generator (let’s say you’re in a 30-amp Class C), you need to be careful running the A/C on the roof along with other appliances in the RV. You can typically run a fridge and an A/C on 30A, however, it depends a bit on that fridge.
It won’t damage anything, mind you, but it might be enough to trip your generator or pop a breaker, which are unnecessary distractions when you’re on the road. You’ll most likely be just fine running your fridge and A/C on 30A service, but you might be limited running anything else while on the road.
Do I Have To Run My Generator To Use The A/C While Driving?
Unless you have a very large solar setup that’s outside of the norm, you have to run your generator to use the A/C while driving. Unless you have one of the kiddos on a generator bicycle (fun stuff and excellent TikTok material), you’ll have to stick with the built-in version.
Your coach or house battery would drain away really fast, so there’s no other option. Since the rooftop A/C isn’t tied to your dash A/C, it’s not powered by the engine either.
Besides, running the generator will also charge your house batteries. It’s a good idea to give your generator a good workout from time to time anyway.
If you have 2 A/C units and you are running on 30 Amps (like when your generator is running) we highly recommend getting a Micro Air Easy Start for your A/C Units. This will ensure you can run both airconditioners while your rig is running on 30 amps. And you could be operating on 30 amps depending on your generator size and even at your campsite.
FYI – Mike at RVBlogger and the NRVTA tested out a similar device called RV Soft Start and they failed. Be sure to go with the Micro Air Easy Start.
Todd from the NRVTA has a great video about how and why these devices work so well. Mike and Susan at RVBlogger have 2 A/C units and they have 2 Micro Air Easy Starts. Check out the video below.
Is It Safe To Run The Generator While Driving?
It’s perfectly safe to run the generator while driving as long as you keep up with preventative maintenance and regular maintenance procedures. For instance, a leaking generator definitely loses some of its safety value, whether you’re rolling down the interstate or boondocking in the wilderness.
Some states do have an issue with running propane generators while driving. That’s something you can deal with by checking ahead of time. As far as gas and diesel, most states are fine with built-in generators running while driving.
Portable generators are a different story and, for obvious reasons, you should never run a portable generator inside your motorhome.
Will I Use More Fuel Running My Rooftop A/C While Driving?
Yes, you will use more fuel if you have your motorhome rooftop A/C running while driving. This is because your generator will suck up about 1/2 a gallon per hour, which will reduce your gas mileage as it adds up over time. At a 1/2-gallon per hour rate, you will burn 4 gallons in 8 hours of driving.
On average, a Class A motorhome holds about 100 gallons in a full tank. The gas mileage on a Class C is more noticeable since the average Class C holds between 25 and 50 gallons. In the middle of the summer, however, it’s probably worth the small sacrifice.
This is especially true if you have family members and pets in the back. You don’t want them panting constantly and going through two gallons of water a day. There’s very little in this world that’s more miserable than being constrained in a tight environment and hot at the same time.
Is It Worth Running Your Motorhome Rooftop A/C While Driving?
It’s worth running your A/C while driving, but it’s also entirely up to you. If it’s just you and a significant other up front, no pets, no kids, then sure, you can get away with just running the dash A/C.
It will keep the cab area fairly cool and there’s no one in the back to sweat uncomfortably and complain. You can also use a curtain behind the drivers cab in a class C RV so the drivers cab stays cooler.
Here are some Pros and Cons about running the rooftop A/C while driving.
- It keeps the entire RV cool so you don’t have to wait for your RV to cool when you arrive at your campsite
- It keeps everyone, including pets, behind the cab comfortable, as well
- Keeps your house batteries juiced up
- It keeps your generator tuned up and broken in
- It’s an excellent option if you need to switch off your dash A/C for driving through elevation changes
- It does take a small bite out of your overall gas mileage
- Propane generators may run afoul of state laws
- Generators could overheat in stop-and-go traffic
It’s one of those rare deals where the cons are not all that extensive. You will need to keep an eye on your battery levels and practice preventative maintenance. But that’s something you should be doing anyway.
Final Thoughts About Running A Motorhome Rooftop A/C While Driving
Running a motorhome rooftop A/C while driving is a common question from new RV owners. Fortunately, it comes with a simple enough answer (not everything on a motorhome is as simple as it sounds). Yes, you can definitely run your rooftop A/C while driving.
In fact, if you spend a lot of time on the road with family throughout the summer, it’s almost imperative. At least for their comfort. It’s not a difficult process either. Just keep an eye out when it comes to state laws. Make sure you practice routine, preventative maintenance on your generator and batteries.
Unless you just want to torture the kids in the back (you’re not alone), running the extra A/C will keep everyone comfortable. Remember, you can also run the furnace on the road in the winter, so you can keep the temperatures nominal all year long.
About the Author:
Thomas Godwin is a full-time freelance writer with a BFA in Creative Writing, a U.S. Marine, and an avid outdoorsman.
When he’s not writing, he’s raising chickens and Appleyard ducks. Thomas also constructs teardrop campers (attempting to anyway) and kayaks the Blackwater River with his wife, two daughters, and his Dobermans.