Is my new rooftop A/C unit bad? (tripped breaker)

[belfert]

I finished installing a new Atwood 15K BTU rooftop A/C last night.  It ran fine for an hour or two.  I started up the generator to make sure all three would run on the generator and they did.  After about half an hour the breaker tripped for the Atwood A/C unit.  Temps were only around 82 degrees and the sun was almost down so no real sun load.

Is this a sign my new rooftop A/C unit is bad if it trips the breaker at only 82 degrees?  I have 12 gauge wire running to it and the breaker is 20 amp.  My other two A/C units have run at 104 degrees outside (and tremendous sun load) without tripping the breaker.

[Len Silva]

If you don't have a clamp on ammeter to measure the current, I would replace the breaker.  Relatively cheap way to troubleshoot and likely culprit.

[robertglines1]

If the breaker in ? has been tripped a bunch it could be weak link. Just a observation.  They tend to get that way.   FWIW.

[luvrbus]

They draw more than the 13 amps they advertize more like 16 to 17 about the same as a Coleman,it will blow cold air our friends have 2 in a S&S and were on 15 amp breakers it didn't work   

[belfert]

I'm going to check for the amp draw later today.  It would be cheap enough to get a new breaker although I've very rarely blown a breaker.  I just rearranged all the breakers in the panel yesterday to accommodate the new A/C unit.  I was trying to balance the load for when I run off a 240 volt circuit.  (My generator is 120 volt and feeds both legs.)

I wouldn't expect any 15K BTU rooftop to work on a 15 amp breaker.  All of my breakers are 20 amp (or larger as necessary).

[HighTechRedneck]

Since they ran fine on shorepower but tripped breaker on generator power, you might check the voltage with the full load of all three running, with compressors engaged, and other typical loads on.  If your generator can't maintain 120V under that load, then the amps would go up as the volts go down.

[bevans6]

Remember that the maximum continuous current for a 20 amp breaker is 16 amps.  Over that and it is supposed to trip after an hour or so particularly if it's installed in a hot location.  I have read of 100% rated breakers being available.  I was going to mention checking the voltage but got beat to it!  

Brian

[TomC]

Sounds stupid, but make sure the black wire coming from the breaker is tight. Vibration from running down the road can loosen it up causing heat and resistance. I installed a computer fan in my breaker box cabinet to cool it in summer. Good Luck, TomC

[Sam 4106]

Tom,
It isn't just a loose black wire that can cause resistance, a loose neutral (white) wire can  cause it too. I would be good to check all the wires in the panel for looseness.

Good luck, Sam

[wg4t50]

Correct,  most 20 amp breakers are dual purpose, meaning both magnetic and thermally tripped.
Yes a 20 amp is actually 16 amp at most in a cool area. They can become maddening on a hot day with a large load that warms them up.
Dave M

[belfert]

The A/C was just wired up yesterday as it is now so I am pretty sure nothing is loose.  The breaker could be bad perhaps.  We are going to check the amp draw right now.

I haven't run it long enough on shore power to see if it trips the breaker on shore power too.  It just happened to be running off the generator when the breaker tripped.  I cannot run three A/Cs off shore power at home as I only have a 30 amp circuit.

[belfert]

I measured the amp draw on the new A/C and it is under 12 amps, but the outside temp is 75 degrees right now.  I am running the A/C units all full blast to try to replicate the issues from yesterday.  I even opened all of the windows to keep the A/C units running.

[wg4t50]

Does the breker trip within a few seconds or a longer time, if longer, you should detect with your fingers the breaker getting hot.  If quick trip, would check the wiring again.
Dave M

[Sam 4106]

Brian,

Just for giggles, if you connected the 12 ga wire from your 20 amp breaker to the air conditioner wires with wire nuts, and you reused the old wire nuts or too large new wire nuts, check those joints. They may be loose. Never re use wire nuts because the coil inside them can stretch and not make a firm connection. It is also a good idea to twist the wire ends together with a pliers and trim the ends even before putting the new wire nuts on. You get more contact between the wires that way. A few tricks I learned from my retired electrical contractor neighbor.

Good luck, Sam

[belfert]

This is a third brand new rooftop so I ran brand new wire for it.  Atwood does not provide a junction box for the AC wiring so I used good quality butt connectors to connect their stranded wire to my stranded wire.

I have no idea if the breaker got hot as it only happened once.  I tried to make it happen, but then my generator broke and I spent the rest of the evening fixing that.