We have started having trouble with our outside package unit A/C stopping on its own, before it reaches the correct temp. I can identify 3 issues:

  1. There are multiple lights (bath, just one light over the kitchen sink, and laundry light downstairs) on opposite sides of the house that go off at the same time as the AC. 220 Breaker in position 3-4 is not tripped. I believe there is a short or loose wire, because after it goes off, it will come back on by itself between 15 minutes to 2 hours hour later. Nothing else is touched, and it comes back on. Even stranger is the same lights will sometimes come on at around 50% full power, but no AC. They will randomly come back to full power on their own. This morning AC was off when we got up, then came on for an hour, then kicked off. Same lights described above were off, then fluctuated between full power, 50% or off. As I checked breakers with a spot light plugged in below the panel, that light will come on and off randomly with nobody touching it.
  2. A separate 15 amp breaker in position 8 also can turn off the laundry room lights described above. This light is on a pull chain and can be turned off from 2 breakers, one being the 220 for the AC.
  3. Last issue. This morning the well pump went off (a home run circuit) and won't come back on. I have an electrician scheduled to come out this week, but no water or AC is not real good.....Any insight would be appreciated.
  • 1
    Since they're dead anyway, shut down all your 2-pole (240v) breakers. Do those "troubled" 120V circuits go altogether dead at this point? Do the now-dead 120V circuits seem like "every other circuit" or "every other row of breakers"? Commented Jul 21, 2019 at 14:37
  • What make and model is your breaker panel? Commented Jul 21, 2019 at 15:28
  • OK. After turning off all 240v breakers, the 120v breaker does not turn the light on. If the 240v breaker is back on, the light goes on. Then if the 120v breaker is turned off, the light goes off. I just don't get how that works..... Commented Jul 21, 2019 at 17:07
  • General Switch - Model MB200-24. Guessing it is the original panel, house was built in 1978. Ranch with a basement, panel in basement. Commented Jul 21, 2019 at 17:11

1 Answer 1


Call the power company and tell them you lost a phase

This will explain all your symptoms. I almost posted this answer before hearing your reply, but your reply confirms it.

The power company should come out and do this for free on a Sunday - they did for me.

This is what is happening. Your supply wire to pole L1 (or the other, but let's say L1) is broken. The 240V loads are connected between L1 and L2. Some 120V loads are connected between L1 and neutral.

When a 240V appliance (pump, water heater, A/C, range, dryer) cycles on, it effectively connects L1 to L2 through its low resistance motor or heater. This energizes L1 at L2’s voltage.

This in turn allows 120V appliances wired between L1 and neutral to power up. This current flow also allows the 240V load to function somewhat; the large load(s) and the 120V load(s) on L1 are in series, running on 120V total.

This is far from ideal, but it's enough that for instance water heaters will warm enough to cycle off again, and the pump may do the same (though I certainly would not push my luck with a pump in a most inconvenient location). Hence the lights cycling on and off "randomly". When all 240V loads are cycled off, the whole 120V leg will be dead.

  • 1
    YES! That was the problem. The power company came out and found the meter was burned out on one side. They put a temp jumper on it so we could function, and I am having the whole box updated this week. Thanks for your insight. We really appreciate it! Commented Jul 22, 2019 at 12:32

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