air conditioner power feed

I have a 1988 funchaser that I'm working on getting back into shape after some years of neglect. It's coming along nicely!

I don't have access to a 30amp outlet at home, so I have an adapter on my AC cable to allow it to plug into a regular 110v extension cord that goes to an outlet in my garage. This is enough to run the AC systems in the camper (battery charger, lights, pumps, etc)

However, when I attach the air conditioner power supply feed to the inlet near the roofline, a circuit breaker on my camper's CB panel trips.

I know the air conditioner works, if I unplug the camper from AC power and plug the extension cord from the house directly into the air conditioner power feed, I can run the air conditioner.

So:

1. why won't the camper's AC system properly feed the air conditioner while plugged into ground power?
a) not enough amps on that circuit?
b) voltage loss from 75' extension cord?
c) something else?

2. How can I overcome this limitation?

3. How do you run the air conditioner at campsites that don't have 30amp power...but have regular 110v AC on a 20amp CB?

4. Will it damage the air conditioner to run it on 110v AC supplied from an extension cord plugged into a regular outlet? Or must it run from the camper's AC bus?

Answer to #1 through #4, You can burn the motor out on the A/C if it is not supplied with sufficient voltage and current. You may be able to run it off a 20 amp circuit by itself but I wouldn't want to do it. The trailer is meant to plug into a 30 amp circuit in order to run everything properly. A 30 amp cord and circuit is essential especially if you will be running the A/C. Using an adapter is okay if you will using everything but the A/C.
The start-up current on an A/C unit is quite high because it starts under load and if it can't get going it will sit there trying and will eventually heat up and burn out. That would be an expensive fix.

RichR said:

The start-up current on an A/C unit is quite high because it starts under load and if it can't get going it will sit there trying and will eventually heat up and burn out. That would be an expensive fix.

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So, if you hear it start right up and run easily, are you out of the woods or might there still be damage being done?

When I have it on a 20amp outlet it starts right up with no hesitation and runs great.

It may be okay. It may sound like it is starting and running normally, but is it? If it is the only thing running on the 20 amp circuit and you are going through a heavy enough, 12 gauge, cord that is not too long, and it is supplying at least 115 volts at the A/C end, all should be fine.

The A/C runs on a dedicated 20 amp circuit in the trailer and that is reliant upon the trailer being plugged into a 30 amp outlet. My dealer tells people not to use the A/C if the trailer isn't hooked to at least a 30 amp circuit.

I sound like "doom and gloom", but I don't want to see anything bad happening to your A/C.

johnpeace -

The formula for electricity is E/R=I,

E (Electromotive force) is measured in Volts, think of this as the "pushing force".

R (Resistance) is measured in Ohms, this is "resistance to current" (electricity) flow.

I (Intensity) is measured in Amps, it is the amount of electricity or "current flow" in a circuit.

In your case, the connection to your house is providing 110 - 120 volts of electrical pressure. This pressure will push current (electricity) through the extension cord. So the question is, how much current will it push? This depends on how much cumulative resistance there is in the entire circuit. The circuit is the complete path that the current has to flow though.

A handy way to think about electricity is to compare it to a water line, the smaller the water line is, the more resistance there is, so you get less water volume. The longer a water line is, also creates more resistance, so this is another factor that causes less water volume to come out of the other end.

In your case the extension cord is the water line. A smaller diameter cord has more resistance then a larger one, so less electrical current will flow through it. The longer an extension cord is, the more resistance it will have, so again, less electrical current will flow through it. Please keep in mind its the wire size inside of the extension cord that counts, the insulation around it is not a factor in resistance, so you can't always tell just by looking at the extension cord, you need to look at its AWG size.

Electrical wire is measured as a "gauge", or AWG (American Wire Gauge) to be more correct. Gauges are funny in that the smaller the number, the bigger the wire. For example, a 14 AWG wire is a larger diameter than an 18 AWG wire. And if you apply the water pipe example, then you will know that the 14 AWG will carry more current flow (Amps) then the 18 AWG.

The average RV air conditioner needs 12 to 16 amps of current flow. I did see some energy efficient models that claimed under 11 Amps, while I was looking this up.

Referring to this extension cord chart, you will see that an extension cord that is 75 feet in length, would need to be at least 14 AWG in size to be able to carry sufficient current to the air conditioner.

Extension cord chart

Add to this that if you plug the extension cord into the trailer cord, now you have added the resistance of the trailers electrical system to the circuit. While this isn't a great deal of resistance, it would explain why you get more power to the A/C when you hook it directly to the extension cord as opposed to the trailer cord.

The strain from not having enough power to the A/C causes the circuit breaker to pop (opens the circuit), this is it's way of protecting the air conditioner.

Another factor to keep in mind, is what other devices in your house or garage are connected to the circuit that you are plugging the extension cord into? The outlet that you're plugging the extension cord into may be on a 15 or 20 amp circuit breaker, but, is the extension cord to the trailer the only thing on that circuit? Most plug circuits will have at least 4 to 6 outlets connected to them, and some even more. The outlets themselves don't use any power, but the things that are plugged into them do, if they are turned on that is. So on a given circuit, you may or may not have enough available amperage potential, even before you attach the extension cord.

The good news is that the circuit breaker on your trailer is doing its job and protecting the A/C unit.

The solution, if an extension cord is necessary, use at least a 14 AWG extension cord, the shorter the better, and plug it into at least a 20 Amp circuit that isn't already loaded up with other things, should work just fine for running your A/C. But do keep in mind that if you start running other things in your camper, TV, refridgerator, etc., you may overload the circuit and either pop the breaker or make the A/C motor strain and run hot, risking damage to it.

Neal

Neal,

That was good! I'm impressed. You use the water pipe method also I see. I have always told people, " If you can figure out how to plumb the water lines in a house you should be able to wire it as well."

I want to put a 30 amp outlet in for the Hi-Lo. It will be at the far end of the house and garage from the service panel so I think I will need to jump up from the normal 10 gauge wire to 8 gauge to compensate.

There was a person on the RV.NET forum that was trying to run his rig from a garage circuit. It kept tripping the breaker in the garage. It turned out that the same circuit also ran his beer refrigerator. It was either one or the other, guess which one he chose.

RichR said:

There was a person on the RV.NET forum that was trying to run his rig from a garage circuit. It kept tripping the breaker in the garage. It turned out that the same circuit also ran his beer refrigerator. It was either one or the other, guess which one he chose.

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A man has to have what a man has to have!... just don't tell my wife

Thanks for the compliment Rich, you gave a great answer too, I checked the post times and saw that we must have been typing at the same time.

I wish I could put a 30 amp outlet in at my place, my service panel is maxed out all ready. Guess I could get a larger panel, but that would be a bit more work then I want to get into.

Neal

Luckily when we built the house we put in a 200 amp service panel in anticipation of electric heat. It turned out that we were able to connect to natural gas. So ampacity is not a problem. I'm thinking of maybe making the circuit a 240 volt, 50 amp circuit then I can run an air compressor or a welder when needed. Then all I will need is a dog bone adapter for the trailer.

i have a 87 funchaser
can't wait to chase that fun
if i use two exstenion cords
one to ac
one to everything else
my ac doesn't trip the breaker...BUT
the compressor won't run more than about 20 seconds
then off 20 seconds
then back on 20 seconds
over and over again
it does blow cold when the compresser is on
i have assumed it was a current problem
while i'm repairing the roof
i would just as well change the ac out then
but i think it's ok
am i right
also what i know for sure
is the thermostat. on the unit
won't let the compressor kick in
unless the temp in the HI-LO is above 72

who thinks my ac is ok
heading to hot TEXAS

Cycling on and off like that certainly is not normal. Have you tried running the A/C on its own 20 amp circuit? When working properly the A/C should stay on until the temperature has reached the level that has been set on the controls. When it shuts off, it should not turn on again for some time. Usually there is a delay time before the unit will turn on again to allow the compressor to drain off pressure, that can be maybe three minutes, more or less.

Sounds like it is low on refrigerant.