Tuesday, March 21, 2023


Why does my RV’s air conditioner hum but it won’t start?

Dear Dave,
My RV’s front roof air conditioner only hums when I turn it on. The fan will not come on to blow the air. —Rhonda, 2008 Fleetwood Flair

Dear Rhonda,
Typically, Fleetwood uses Dometic air conditioner units, but they operate similar to the others with a compressor and start capacitors. The first thing I would check is the voltage coming into the rig, as low voltage from the distribution center will not have enough “oomph” for the initial startup. Electrical expert Mike Sokol did a test on the initial amp draw for the SoftStartRV unit and saw some of them initially pulling 43 amps!

Test power with multimeter

You should be able to test the power at the campground source with a multimeter. I would also check the voltage at the air conditioner; however, this is more likely best left to a certified electrician. You can check voltage with a simple Klein meter like this one at some of your outlets. You will want at least 115 volts.

Next, check your return air. There is a filter under the vent area and if it is plugged, it will limit air flow and create a higher amp draw, as well.

This one is a non-ducted unit, but the filter is similar. If it is dirty, clean it with warm water and soap and rinse it out. Let it dry before reinstalling.

May be blocked return air

Another issue could be a blocked return air if the baffle for the ducted air vent gets loose and breaks away. I have found some that were installed very poorly with a single piece of duct tape and they pulled away and blocked the air coming in. I would then check to see if the fan is spinning freely. You should be able to access this through the return air inside the rig.

You can see by this photo the return air on the left and the forced air with fan on the right. See if the fan moves freely. If not, the motor could be shot or something is blocking the fan, maybe a broken fin or the Styrofoam around it has broken loose.

If the fan turns freely, you will need to have someone test the compressor and start up amp, as it may be time for a new one. You might be able to install a SoftStartRV component if it is just weak.

 You might also enjoy this from Dave 

How can my RV’s roof air conditioner run more efficiently?

Dear Dave,
I’d like to improve the efficiency of our roof air conditioner. The factory shrouds are black. I’d like to paint them white. Second, I’d like to insulate the pipe from the compressor to the evaporator. Thanks. —Joe, 2019 Coachmen Pursuit

Read Dave’s answer.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

Read more from Dave here


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25 days ago

Is it just me or does 43 amps at start up seem about 20 amps to high? If you have 2 start up at the same time, 86 amps? Tells me don’t buy Dometic if that’s the case.

Rodney Lacy
25 days ago

Probably bad capacitor. Very common problem. 45 year HVAC tech.

Stephen Snure
25 days ago
Reply to  Rodney Lacy

I agree with Rodney that the capacitors should be checked, assuming the RV owner is comfortable doing so. I’ve had two Coleman Mach 15 air conditioners on my 2011 American Tradition motorhome fail as a result of bad fan capacitors (oval 7.5mfd 370 or 440 VAC). They’re about $10-$15 on Amazon and were very easy to change.

Thomas D
25 days ago

Why does it hum?
It doesn’t know the words! Seriously, mine did hum and muddabber wasps had built nests inside the housing.
I removed the cover and cleared out the nests. Bee careful.
You can try it from inside by removing the covers and turning squirrel cage blade to see if it rotates.

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