AC popping house breaker.

[canuckrv]

I was doing some work on my motor home in the driveway and due to the heat i had the AC on. When it is on high cool everything is fine when I turn it to low cool it pops the 15 amp breaker in the house. In my mind this is backwards I figure low cool would draw less amps not more.
This is not really a problem (i hope) just more of a curosity.
thanks

 

[Just Lou]

My guess is, that when on high cool, the compressor was running continuously and not drawing enough current to trip the breaker.  Possibly, on low cool the compressor was cycling and the restart current was sufficient to trip the breaker.

Start-up current required for a compressor, especially with possible existing high head pressure, is much higher than the normal operating current.

 

[BCinTOR]

That is curious.

I put a 30 amp outlet in our driveway.  I couldn't run the fridge plus AC before departing on the 15 amp line.

This is the box we used: http://amzn.com/B0009R3DQC

A professional electrician did the install as I didn't want to hurt my house's resale value in the future with a not to code install.

 

[Gary RV_Wizard]

In most RVs, the difference between Low & High is just fan speed. The roof air compressor either runs or it doesn't - there is no high or low.  Do you have basement air? Basement air systems have a two stage compressor and it can cycle one or both, which is intended to let it run when power (amps) are limited. Your thermostat might be using that capability s High and Low.

 

[canuckrv]

no basement air just an old rooftop.

 

[travellerz71]

I can think of several things that could happen on low fan the unit could be cycling on low evaporator coil temp or the head pressure could be building up due to the low airflow.

 

[cvrvr]

Unless your are using a 10-3 extension cord no longer than 50 ft, my guess it that the voltage drop is to great.

George

 

[canuckrv]

if it was the extension cord would it not also blow the fuse on high cool?

 

[Gary RV_Wizard]

Probably.

 

[WhiteEagle]

Any chance your battery charger kicked in about that time which collectively would have tripped it?
Do you have your load share set to less than 15A?

 

[TheBearAK]

I agree with the cycling as mine does that.  You can hear it put a load on a generator sporadically when on low, but on high it is continuous load.

Startup load is greater than the continuos.  My AC units each draw 7-9 amps continuously when turned on high.  I would guess that when they first start up, it is pushing 13-15 amps.

 

[Gary RV_Wizard]

I don't know of any rooftop a/c that has a two stage compressor, so I suspect that your High/low thermostat setting controls nothing but fan speed. Difference in amp draw is probably less than 1 amp between high and low fan. As others have already suggested, it seems probable that the lower air flow is allowing the compressor to cycle on/off and the compressor start-up load is what is tripping the 15A breaker. The amp draw at compressor start is typically about 2x the steady (run) amps, and a 15A circuit often does not have enough spare capacity to handle that. You didn't say if there is anything else sharing that breaker in the house, but there very probably is. Few household circuits are dedicated to a single outlet and often are daisy chained to several outlets and/or lights.

 

[canuckrv]

Nothing else on that circuit. Must just be the cycling. Thanks everyone.
One day I'll get the 30amp plug installed.

 

[Gary RV_Wizard]

If the wiring isn't too old, you may have 12 gauge wire rather than 14 gauge. In that case, you could safely switch to a 20A breaker and likely solve the problem.

 

[canuckrv]

Just an update, it was the blower motor causing the problem the bearings are seizing there is no replacement motor so now I am looking for a new ac