I have noticed my 30 amp main breaker keeps tripping when I am running the A/C. Obviously I know I can't run the A/C and microwave or the A/C and the coffee pot.  But, with just the A/C, the main will trip.  Usually after it trips, it won't immediately reset. I have to wait a while, I am guessing for it to cool down.  Should I look at replacing the breaker? Or could it be my A/C going out?  I know I have a Coleman Rooftop A/C.  I also know it isn't the original unit that came with the camper. I have included pictures of the power panel and breaker that keeps tripping.

I have a 1984 Shasta Roadmaster in case y'all have forgotten.  Have a good day and thanks for the help!


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How long until it trips? 30 amps is a lot for a single roof unit to draw unless turning it on is introducing a dead short. Does it not have its own breaker?

 It is on its own breaker.  I can run the fan with no problems but, within 15 minutes or so of the compressor running the main breaker trips.  Not the breaker the A/C is on.

You might have a weak breaker,, I can understand the a/c unit drawing 30 amps to initialy get started, but it shouldn't be drawing a continuous 30 amps running.  My a/c is on a 30 amp breaker and seems to run fine after start-up.

You mentioned aftermarket, (not original a/c unit that came with camper). This could possibly be a larger unit intended for a larger coach.  I would try another breaker 1st.

I kind of figured the breaker was weak.  If the A/C was drawing too much power on start up, the breaker should trip immediately after start.  Usually the breaker will trip after 15 minutes or so of use.  

I don't think the A/C is too big, I can see where the old A/C was located.  This unit looks to be smaller. 

Where would I find a replacement breaker that fits? Or would it be easier to replace the whole power panel?

You state that it is not the breaker that the AC unit is on that trips; but the main 30 amp breaker.  Are you running other stuff besides the AC unit?  In the campers that I have had, the AC units had 20 amp breakers, and it sounds like yours may be the same.  If the 20 amp breaker doesn't trip, then usually it is the combination of the AC unit and something else.  Check your shore power cord and clean the plug contacts with fine sandpaper or something like that.

I'd replace the breaker, examine both the shore power cord male and female connections to see if there is any black, brown or other discoloration from overload/ poor connection as Richard says. If you see this you should consider getting either a new heavier connector cord or replacing the male or female connectors on the existing cord. RWT, what do you thnk of a hot box with power surges?  Wally world has a neat little tester to see if shore power is bad, ungrounded or too hot or power surges... which causes breakers to blow.   Campground electrical systems are notoriously unreliable shore power. 

I'll try cleaning the contacts on both the camper plug and extension cable.  It wouldn't surprise me if the shore power here is dirty.  Maybe a surge suppressor is needed? I'll take a look at Wally World and see what they have.  Thanks for everyone's help!

The only other thing running is the electric water heater,  Once it reaches temperature, it shouldn't be drawing too much power.

For my power cable, the camper only has a plug.  I have to use a 30amp extension cord for shore power.  I am seeing on the female end of the extension cable it looks like it has gotten "hot".  I will clean the contacts and try that. 

I'll ask John T  about this. sending him a message so he can ponder this probelm too. 

Far as I know those breakers are Thermal Magnetic, the Thermal element trips out only after long continuous overload conditions while the Magnetic trips if theres a sudden high current surge like a short etc. The fact that the she trips out only after shes been running a while tells me its the Thermal HOWEVER I dont understand why prior to that the thermal on the smaller 20 amp AC breaker doesnt trip out HMMMMMMMMM,. One way that can happen is the AC unit is okay (cuz its own 20 amp is holding) but theres another current draw passing through the main breaker like an electric hot water heater (if it has an electric unit) or the converter or the fridge if on electric but those don't draw much???

Of course, to answer those questions all you need is an ammeter reading on the AC unit itself and any electric water heater and on the main circuit. Id expect the AC (depends on size) maybe in the 10 to 14 amp range which shouldn't trip either its 20 or the main 30 amp breakers but if its much higher THEN THE AC IS AT FAULT and it doesn't sound like the start up circuit but the run circuit. I don't think that AC is a capacitor run unit???? Im NOT there to look) but if it were that could be faulty, still a reading of its current will tell the picture!!!

Those breakers can get lazy over time and perhaps the main is weaker then the AC (but wow its a 30 amp and still shouldnt trip with a 15 amp load UNLESS theres another load like a bad hot water heater element????d???) for no more then the cost if you cant take the AC and hot water heater current readings, Id try a new main breaker. If you take the old one to an electric supply house or even Lowes or Home Depot that may match it however you may have to go to a Mobile Home Supply Shop or an RV dealer if its any special RV/Marine Panel????

My answer has to take educated guesses not being there and not knowing if theres any electric hot water heater or a short etc but a few current readings will tell the problem. Maybe a short or the water heater or the Converter are at fault since the AC 20 amp breaker holds in yet the 30 amp main trips, sure breakers can be weak, but not being there Ima thinking the AC and breakers are okay but theres another pretty good load drawing current in addition to the AC. Maybe unhook any water heaters or Converters and just run the AC n see what happens????


John T At the Florida Flywheelers Show in Fort Meade Florida 80+ degrees whew lol I need AC

I think the main 30 amp AC breaker is doing what it's suppose to.Add up the roof AC and the hot water heater.That's 30 amps right there.Include the AC to DC converter,fridge maybe running on AC and any resistance in the shore power cord.

Now your rig is pulling well over 30 amp's.

Shut off the water heater and see if it still trips.




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