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Ask Dave: Owner’s manual says I can run roof AC on 110-volt power. Shouldn’t it be 30 amp?

Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. Today he discusses an RV’s roof air conditioner.

Dear Dave,
We have a 28-foot Zinger made by Thor. Even though the owner’s manual says you can run the AC on a 110 outlet, I’ve heard that this will shorten the life of the unit, as opposed to running on a 30 amp. I also heard that you should never run the AC on low because it’ll freeze up. Is this true or false? Thanks, Dave. —Ron

Dear Ron,
The typical roof air conditioner operates on 120-volt power supplied by the distribution center of an RV. This is often referred to as “110 volt.” However, it should be somewhere close to 120 volts. This 120-volt source can be sized for 15/20-amp, 30-amp, or even 50-amp power.

The typical roof air conditioner will run at approximately 14 amps at full draw, with older units (pre-1990) pulling as much as 18 amps. So, when your question refers to “110 volt” listed in the owner’s manual, I believe you are referring to a residential-type outlet such as a garage versus a 30 amp referring to a campground source like the one pictured, right?

Most of your residential outlets such as this are connected to a 20-amp circuit breaker, which would typically be enough power to run your roof AC. However, these are usually connected to other outlets in the garage that have refrigerators, air compressors and other energy-drawing items. Plus, when you plug in your shoreline power of the RV and turn on the roof air conditioner, it is typically not the only thing drawing power, as you probably have the refrigerator or water heater on too. These all draw power as well as draw 12-volt power from the house batteries, which means the converter/charger will turn on occasionally.

Use a surge protector

What can harm your compressor and fan motor in a roof air conditioner is running on low voltage. The ideal voltage is 120 volts and nothing lower than 113 volts as the unit will still run, but so will labor and increase in amp draw and eventually go bad. Using a surge protector such as this Surge Guard model will monitor the voltage, show the amp draw, and shut down if the voltage drops below a safe level.

Read more from Dave here

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tom
7 days ago

Perhaps purchase the softstart system.

Steve Hericks
7 days ago

Numerous misconceptions regarding the 120V power system; 1) The 120V US power system power tolerance is +5%/-10% (126-108VAC). Equipment designed to operate on this system is tested and will operate safely on this voltage range. Designers expect to frequently operate at lower voltages which is why they are designed for and rate as 110V or 115V (see equipment labels). If the starting loads cause voltage sag below 108V, it MAY cause starting problems. 2) The power pedestal shown contains a 20A/120V GFCI receptacle, not a 15A. The ‘sideways T’ hot terminal is the visible identifier. In order to connect a single device to draw 20A, a 20A plug should be used (NEMA type 5-20P). A 20A plug has one horizontal and one vertical terminal. 3) IF a 20A device is connected, it must be the only device on the circuit (NEC requirement) 4) Receptacles rated at 15A and 20A, are only rated to provide 80% of this power continuously (12A and 16A respectively,NEC requirement). A/C is a continuous load.

tom
7 days ago
Reply to  Steve Hericks

Excellent answer. I learned some additional information. Thanks.

billh42
7 days ago

Dave,
You only answered half the question. Re the question about the AC freezing up on Low speed. Yes, in extremely humid conditions with the fan set Low the evaporator could ice up. However, the freeze sensor mounted on the evaporator will sense this and shut down the compressor (fan keeps running). Once the ice melts the compressor will restart. Most people run their AC in the Auto Mode and let the temperature differential sensed by the thermostat determine the fan speed. Once the interior is sufficiently cooled down and the humidity is lowered evaporator freeze ups would be rare regardless of fan speed.

T. Elliott
7 days ago

Minor inaccuracy – the T-shaped slots on the right-hand receptacle of the campground pedestal picture indicates it is a 20 amp receptacle.
Your residential receptacles may be 15 amps or 20 amps; the T-slot is the indicator!

Larry Lee
7 days ago

Yes, a surge guard will help if used as shown in the photo. However, the question relates to a household outlet so my question is: “Will a 30 amp surge guard function properly if connected through a dog-bone adapter to an outdoor outlet at my house.

David Solberg
7 days ago
Reply to  Larry Lee

Larry,
Yes, it will help on a residential outlet. Just need to use the 30 amp female/20 amp male adapter.

Dan
7 days ago

For what an RV costs a built in surge protector should be standard equipment. Harder for someone to steal it too.

Bob p
7 days ago

Newbies have so much to learn and dealerships don’t take the time to educate them. I don’t think I’ve ever had a delivery walk through that lasted more than 45 minutes. If a newbie doesn’t ask questions as the tech is explaining the features of the RV they just buzz right on through and half of what they’ve been told floats off into thin air. A good dealership would make sure the buyer understands how everything works.

Leonard Rempel
7 days ago
Reply to  Bob p

Agreed. My walkthrough was 30 minutes, and due to Covid the tech barely answered a question. I had done so much research beforehand, I was better prepared than a normal newbie, but new owners must take matters into their own hand! We can’t blame the dealer for our lack of preparation and knowledge of what we are about to buy. No one buys a house and blames the former owner for things that go wrong. The person you look at in the mirror is responsible.

Tommy Molnar
7 days ago
Reply to  Bob p

I also think you should be able to spend a night at the dealership, learning how stuff works, and finding out what DOESN’T work while you’re still there. Unfortunately, that will never happen and the excuse would be “insurance issues”. We did something like that at the dealer we bought our trailer at in SLC. Of course, he’s now out of business.

Irv
7 days ago
Reply to  Tommy Molnar

We stayed at a nearby campground for a few nights after we picked up the RV.

In any case, don’t go on a long trip a long way from home or from the dealer before staying in the RV for at least a couple of days to see how things work and learn what you need to add. Additions might be storage containers, shelving, cooking utensils, etc.

Tommy Molnar
7 days ago
Reply to  Irv

Good idea.

Bill
7 days ago
Reply to  Bob p

We bought a barely used Lance cabover camper from a big dealer in Bend OR. During the walkthrough we asked a lot of questions and even found a gas leak at the changeover valve between the 2 tanks, which was fixed on the spot. We took delivery on that 40° day after having heating and AC thourougly explained.(both worked off the same thermostat)
4 months later on a trip to Montana a freak heat wave hit and when I turned on the air it just blew 90° ambient air! Cover off exposed a completely cracked high pressure pipe .. So a new a/c unit was put in.
The dealer in Bend told me (exact words) “that is your problem, you should have pointed that out in the walkthrough”
Lesson learned .. Have the a/c tested when in an ambient environment above 65°.(and don’t buy from a sales guy named ‘Dutch’.

tom
7 days ago
Reply to  Bill

Test and question everything before the $$$$$’s.

Bob p
6 days ago
Reply to  Bill

We also had an A/C problem in a Class A during walk through the A/C was running and very comfortable. With the ducted air we didn’t know the front A/C was locked up and the cool air was being provided by the rear unit. Lesson learned, go up and check to see if it’s running, a $1800 mistake.

Steve Hericks
7 days ago
Reply to  Bob p

(I’m former RV plant engineer).

Paid repair and modification is the bread and butter of RV service. If YOU want a change or YOU caused a problem (especially through ignorance), THAT is the kind or work they want to do AND receive a premium profit for. YOUR IGNORANCE is their protection and what keeps their lights on. Warranty work is paid by the manufacturer at an unprofitable margin. They only make money on paid work.

Truthfully, 3 things or 15 minutes duration is a standard for any educational training. Beyond that, you will not remember what they said. If you think an all day walk through will be useful or retained by you, you are mistaken. They know this too. Your ‘training’ is not in their interest, only the appearance of training (so they can say ‘I told you so’).

RV manufacture is like sausage making. RV dealers rely on an RV being used little in the ‘warranty period’, hoping that by the time you get outfitted and on the road, most or all of the warranty period will pass.

Bob p
6 days ago
Reply to  Steve Hericks

True, example Nissan CVTs are the worst in the industry and they know it, when talking with a couple of engineers at a softball game that question was asked, their answer: upper management knows about it but their attitude is if it makes it through the warranty period that’s all that counts! Forget about repeat customers! I know that’s not RV related but…