Home Air Conditioner breaker question/problem

Factual Questions
1

I had an issue where the wires in the whole-house AC were getting caught in the fan. In fixing that, I was checking for voltage, and there was 110 VAC between the starting capacitor and the shell of the box. I switched off the AC breaker, but there was still 110. I switched off the furnace breaker also, but there was still 110 between the cap and the shell. There’s a little box with a blade cutoff switch (not sure of the correct name) that I pulled out, and that finally killed the 110.

I’ve re-routed the wires so they don’t get caught in the fan blade, but I’m concerned about the breakers not killing the power.

Is this a problem? (Yeah, I probably already know the answer, but maybe there’s some weird wiring pattern used by HVAC installers.)

More generally, any suggestions? I have already found one pair of circuits that were cross-circuited, but I wouldn’t expect that from a dedicated 240V AC circuit.

Is it more likely the furnace circuit or the AC circuit that’s miswired and providing the voltage?

2

the blade cutoff switch is there so a person knows that device is de-energized to safely work on it. this can be after a circuit breaker.

you need to find the breaker that is feeding that blade cutoff switch.

seeing as how you have found errors i would inspect and map and label the whole house.

3

I’d start by following the 240 line for the AC back to the breaker panel. Ideally, it will run uninterrupted, but in the real world, it may visit a junction box or two, where it may have been cross-connected to another circuit. If the wire checks out OK, somebody may have done something dorky like connecting one leg to the AC breaker and one to an adjacent 240 volt breaker for something like a dryer or range.

The breaker for the furnace should have nothing to do with this.

4

You are likely measuring the stored voltage in the capacitor. A good capacitor can hold a charge for a long time.

5

Not AC, it can’t.

6

True. But a voltmeter set to the AC position can still read DC voltage, albeit inaccurately. The converse of course is not true.

Our OP hasn’t really given us enough info to do detailed troubleshooting.

7

this does seem to be a situation with problems and not enough information (if there could be enough information for this situation over an online forum).

the stored voltage in a capacitor (unless shorted) would discharge slowly.

the voltage disappered instantly with the removal of the blade cutoff switch (which might be called a nonfusible disconnect).

my guess would be the disconnect.

8

It was 110 Volts AC, not DC. DC showed some transient numbers briefly each time I measured it, then dropped down to near zero. (And a capacitor with charge wouldn’t hold 110 for a long time, then suddenly drop to 0.)

I have to admit, I haven’t tried to track down the problem yet.

I don’t understand. Your guess for what? The disconnect, at least, worked correctly.

And I’m not expecting people to diagnose the problem over the internet. I was mostly just making sure there wasn’t some weird thing about AC installations that isn’t common knowledge. You don’t always know what you don’t know.

9

my guess for why the voltage disappeared. the disconnect did disconnect something.

still you have problems.

the wires should be routed so to be held securely and protected in a jacket. either they weren’t or the installation has deteriorated.

there should be a circuit breaker marked AC that protects and disconnects all power to the AC.

all the power to the AC should be shut off by a single safety disconnect.

you found wiring errors in other circuits. in this case you either have multiples paths and/or unlabeled/mislabeled circuits.

10

During dinner tonight, my wife mentioned that the oven time was about a half hour off from the microwave time. After a little back-and-forth, the lightbulb went on.

Our oven has a feature that if there’s a power failure, it holds the time, and resumes when the power comes back on. It also shows a (dim) “PF”, so you know the power went out. That way, if it goes out during cooking, you can figure out how long it was out, so you know if it will affect the cooking.

So yeah, the AC and oven circuits are mislabeled, and I was actually turning off the oven. (There’s a third double breaker, for 30 amps, but that one is labeled correctly.)

The problem I have now is that the AC circuit, labeled “Range”, has a 50 amp breaker, and the oven circuit, labeled “AC”, has a 40 amp breaker. Both the oven and the AC are rated for 40 amps. The wire going to the AC is AWG 6, which should be able to handle 50 amps.

I can’t tell what size wire is going to the oven, it’s above the finished part of our basement. I got behind the oven, to the oven outlet, but all I can tell is that the wire is thick. The oven cord is 8 gauge (with a 10 gauge neutral), if that helps.

I think I’m OK, though, and just need to re-label the two breakers. The 50 amp breaker should be OK on the 6 gauge wire, and it shouldn’t matter if the wiring to the oven is 8 or 6 gauge. Neither appliance needs 50 amps.

Does this sound safe and to code?

11

everything after the circuit breaker, the wiring and all the things powered on that circuit, determine the size of the circuit breaker. if the wiring in the wall for the oven is 6 or 8AWG then you are sized right.

i would give all your wiring an inspection and mapping if you’ve found a circuit cross wired and two mislabeled.