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[Shop-talk] AC compressor is tripping 20A breaker

Subject: [Shop-talk] AC compressor is tripping 20A breaker
From: TR3driver at (Randall)
Date: Sat, 9 Jul 2011 18:26:11 -0700
References: <MTAwMDAxNy5tY2ZldHJpaQ.1310250647@quikprotect>
> The 20A panel breaker is 
> tripping in an odd way also: 

That suggests a defective breaker.  They don't last forever.  It's not a
Federal Pacific, is it?  If so, it's time for a whole new panel.  If not, I
would probably start by swapping the breaker that holds with the breaker
that doesn't.

> If there is more resistance in the circuit, would 
> that cause the circuit to trip,

Yes it could, for a compressor.  The compressor motor draws a LOT more
current when it is starting, so if it can't get started promptly (or drops
below normal running speed), then it will blow the breaker.  Easy test here
is to check the line voltage near the compressor, first with it not running
and then with it running.  If it drops by more than about 5%, you've got a
(potentially dangerous) wiring problem.

Depending on how your system works, it could also be a bad thermostat or
wiring to it.  Most systems will not start successfully against full head
pressure, so there is some minimum "off" time before the compressor can be
started again.  If the thermostat or wires let the compressor stop and then
tell it to immediately start again, that could cause blown breakers.

Also check the condenser fan (the one that blows hot air).  If it doesn't
always start for some reason, or is running backwards (don't laugh, I've
seen it) that could cause problems.

Could be several other faults with the compressor or the rest of the AC
system, but those tests are probably best left to someone who knows a bit
more about it.

> The owner wants to put in a
> higher amperage breaker, which I don't consider a safe solution. 

I'm speechless.  I think I'd be tempted to call his fire insurance company,
and tell them what he said.  Unless of course you are interested in buying a
pile of smoldering rubble.

-- Randall  

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