My main circuit breaker trips if we start the microwave when the A/C is running. Today when it happened, I forgot to turn off the AC before resetting the breaker and the A/C wouldn't start. I turned it off at the thermostat, set the breaker, and turned on the A/C and it ran.Rig is a 2000 Coachmen Class C 30 amp system with a Dometic rooftop A/C unit.This started last summer so I replaced the main breaker: T&BType TB 120/240 VAC Cu/Al HACR Type UL1 POLE SR-100 E162469 LR102619A/C works fine by itself and the thermostat is set to Auto and Lo.Do I have a capacitor or something going bad?I'm pretty handy but don't know what to look for or where. Can I be low on Freon or whatever they use now?Thanks!-----------UPDATED 06/20/2015------------The issue was originally caused by a 14-year-old breaker getting weak. It was accidently replaced with a 20AMP breaker instead of a 30AMP. This replacement breaker continued to trip because it was below the required capacity to handle the load and was working as designed. A 30AMP replacement is on order.

A 30 amp system will NOT run the AC and microwave at the same time. The breaker did its job.

Jack_Diane_Freedom wrote:A 30 amp system will NOT run the AC and microwave at the same time. The breaker did its job.Ours run fine together,30A with a 13.5k a/c unit.

Now I run A/C and Microwave on 30 amps in most of the places where I'm stuck with30 amp (not all).One question: When was the last time you went, as the song is titled: Up On The ROOF,, with a tool kit and removed the covers from the A/C and gave it a good cleaning,,Epically the condenser?As heat incrdases and temp's in the system rise. pressure builds, the compressor works harder and harder and....... CLICK goes the breaker.

Wiz wrote:I'm pretty handy but don't know what to look for or where. Do you expect two high-wattage devices to run at the same time in your coach?

Turn the hot water heater to LP only and the refrig to LP and see if the breaker trips.

Main breaker trips with A/C and Microwave on.->RESOLVED

75 Replies

rbinc
Explorer
Jun 22, 2015
smkettner wrote:
Is the main and AC paired? I would swap the AC wire with the MW as both should have 20a breakers. Possible get a 30/15 and a 20/20 to have a low draw item paired with the main. Breakers are more sensitive as they get warm so having two high draw items together can build a little extra heat.

Thank you. This is exactly what I encountered yesterday. AC trips every few days, out of the blue. Yesterday when it happened, noticed that the paired main 30 and AC 20 was very warm, even hot.

Swapped the AC 20 with the MW 20 and today, no problems and all the breakers feel cooler to the touch.

Was hoping I made the right deduction and decision. Full time with 2 cats and the AC absolutely has to work.

Thanks much!

Robert
MEXICOWANDERER
Explorer
Jun 20, 2015
Been there...
Done that...

Glad you're fixed. See, it was a weak breaker sorta.
myredracer
Explorer II
Jun 20, 2015
Oh my... :R

Thanks for posting the solution (holding back a snicker, lol).

Wiz wrote:
MYSTERY SOLVED - OP IS AN IDIOT!!!

Ok so I'm the OP, and I discovered yesterday while checking the connections that the replacement breaker I installed last summer is a 20A NOT a 30A.
Wiz
Explorer
Jun 20, 2015
MYSTERY SOLVED - OP IS AN IDIOT!!!

Ok so I'm the OP, and I discovered yesterday while checking the connections that the replacement breaker I installed last summer is a 20A NOT a 30A. :o Apparently I either didn't get what I ordered or I ordered the wrong breaker and didn't notice when I installed it.

Thank you to everyone who analyzed the issue and offered solutions.

The original diagnosis was correct, the 14-year-old breaker was getting weak and tripping. I have a 30AMP replacement breaker on order.

Does anyone need a 20AMP breaker? Slightly used...
Wiz
Wiz
Explorer
Jun 16, 2015
pianotuna wrote:
Hi,

Have you tightened all the connections in the breaker box?

Is the microwave plug accessible and firmly 'planted' in the outlet?

If possible check the outlet for the microwave. If it has 'stab' connections, replace it with something that has screw terminals. If you replace it, use one of the new ones that 'grab' the tines of the plug.

I'll check all the connections in the breaker box this weekend. The shore power cable is hard wired where it mounts to the 12v converter, I'll check those connections too. I'll also be cleaning the blades of the power cable.

I know the microwave plug fits tightly in the mw outlet.
j-d
Explorer II
Jun 16, 2015
Somehow I thought an OP here let the compressor start first then the fan. Unlike at home, the goal here is to give the compressor the best chance to get started on limited amps.
Kit_Carson
Explorer
Jun 16, 2015
Triker33 wrote:
Turn the hot water heater to LP only and the refrig to LP and see if the breaker trips.
I have to change my water heater to LP to use the AC & microwave. I never thought about the fridge. Thanks for the suggestion...
ktmrfs
Explorer II
Jun 16, 2015
j-d wrote:
If you're running FAN on AUTO, something counter-intuitive happens. You're saving power, but.... When the Thermostat is satisfied (it's cool enough) Fan shuts off and Compressor cuts off. OK, good. Then Thermostat calls for cooling again. Fan AND Compressor try to start at the same time. You draw the Start Amps for both simultaneously. Some OP's here have built a delay circuit so one starts a few seconds before the other. I forget which they start first. Modern residential units run Fan a few seconds before Compressor and leave it running a few seconds after Compressor cuts out. Idea is to get the air moving before cooling starts, then take the last of the cool off of the evaporator coil after the refrigerant flow starts.

the mod I did, mostly to help starting from a small generator, is to add a 15 second time delay to the fan after the thermostat calls for cooling. this allows the compressor to get started and running and the genertor to recover, then the fan motor kicks in. Fan isn't a big load, but they also are usually a split phase motor or only have a small starting cap, so it does cut down on the total starting current draw. Every little bit helps.

the other way around is how my house unit runs, but there the objective is different. Starting isn't a problem, but you want to eak out every bit of cooling efficiency so gettting air moving over the coils first and extracting the last bit of cold air from the coils is what is needed.
dougrainer
Nomad
Jun 15, 2015
IF you have a wall tstat, then there IS a delay on the compressor for both Dometic and RVP. The fan on both on HI only pulls about 3 amps and the start draw is nominal for the fan. Doug
time2roll
Nomad
Jun 15, 2015
My Dometic delays the compressor a bit. It would be better with a fan delay but I am not the engineer on this.