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Old 12-25-2011, 03:08 PM   #1
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Help, 110 V from each leg but no 220 between legs


My central air conditioning air handler, with electric heat, suddenly will not run. I measured the supply voltage to the breaker at the air handler and there is 110 volt from the black wire to ground and 110 volts from the red wire to ground. No voltage registers on the meter when measuring between these black and red wires.

I checked the meter on another 220 volt circuit and it works. Any ideas?

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Old 12-25-2011, 03:16 PM   #2
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Help, 110 V from each leg but no 220 between legs


That is what you should be getting. If the unit is not running, and there is voltage, next thing is to check to see if the contactor, when pushed to close the circuit will start it, along with checking the capacitor for bulging. The cap looks like a small soda can, and would be in the same area, behind the access panel.

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Old 12-25-2011, 03:22 PM   #3
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Help, 110 V from each leg but no 220 between legs


Whoa Gregzoll, if that is a 240 volt circuit (as OPS states) he should be getting 240 volts from one hot to the other, certainly not zero. The only way I see you getting zero volts hot to hot on a 240 volt circuit, and 120 hot to ground on each leg, is if you were pulling 120 volts for each hot off the same bus bar at the panel, in which case that is exactly what you would read, but the unit would never have worked. Perhaps one of the experienced electricians can answer this puzzle. You didn't switch out the breaker by any chance?
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Old 12-25-2011, 03:27 PM   #4
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Help, 110 V from each leg but no 220 between legs


Quote:
Originally Posted by Daniel Holzman
Whoa Gregzoll, if that is a 240 volt circuit (as OPS states) he should be getting 240 volts from one hot to the other, certainly not zero. The only way I see you getting zero volts hot to hot on a 240 volt circuit, and 120 hot to ground on each leg, is if you were pulling 120 volts for each hot off the same bus bar at the panel, in which case that is exactly what you would read, but the unit would never have worked. Perhaps one of the experienced electricians can answer this puzzle. You didn't switch out the breaker by any chance?
Thanks Daniel, I did not catch the zero across legs. Could just be a bad disco outside. I wonder that now that you mentioned it, if they may have a tandem vs a dual pole, or one of the panels, that if you do not place the breaker in one of the right spots, you get the same phase off the panel. That would make more since on the 110 on both legs.
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Old 12-25-2011, 03:28 PM   #5
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Help, 110 V from each leg but no 220 between legs


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Originally Posted by petergun1 View Post
I measured the supply voltage to the breaker at the air handler ...
go back to the panel and check what you have there

Quote:
Any ideas?
something very fundamental is seriously out of whack.

hth
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Old 12-25-2011, 03:29 PM   #6
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Help, 110 V from each leg but no 220 between legs


Quote:
Originally Posted by petergun1 View Post
My central air conditioning air handler, with electric heat, suddenly will not run. I measured the supply voltage to the breaker at the air handler and there is 110 volt from the black wire to ground and 110 volts from the red wire to ground. No voltage registers on the meter when measuring between these black and red wires.

I checked the meter on another 220 volt circuit and it works. Any ideas?
Where exactly are you reading these voltages? It is not uncommon to read backfed voltage if you have a leg open. Do you have fuses inside your air handler? You mentioned a breaker, is that the panel breaker?
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Old 12-25-2011, 04:09 PM   #7
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Help, 110 V from each leg but no 220 between legs


One of the hots is open. You are reading the 120 volts on the dead leg through a backfeed from the AC.
Several possibilities. Assuming you have not been working in the panel and this was functioning previously.
1. The breaker is bad.
2. The breaker has a bad connection to one bus.
3. One of the wires in the cable has come loose.
4. There is fuse in the AC disconnect that one of them has blown.

If you have been working in the panel
1. Tandem or mini breaker used instead of a double pole 240 breaker.
2. In some panels the double pole breaker can be installed so both legs are on the same bus.
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Old 12-25-2011, 04:24 PM   #8
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Help, 110 V from each leg but no 220 between legs


Let me thank everyone that replied. The zero voltage was measured at the air handler breaker. The panel breaker did show 220 volts, so I went back to the air handler breaker and removed two wires that were wired to the supply side of the breaker. These wires lead outside to the air conditioning unit. The heater now works and I will have to figure out what those wires supply in the next couple of days -- it's raining right now.

A little info: I live in a small southern Mississippi town where until four years ago building regulations were almost none existent. The process entailed paying ten dollars for the permit, no one ever followed up. Essentially you could do whatever you wanted. Who know what I will find when I open the side of the air conditioner.

Again, thanks for the quick and valuable replies.
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Old 12-25-2011, 04:32 PM   #9
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Help, 110 V from each leg but no 220 between legs


Sounds like the feed to the outdoor unit. I wonder what your original problem was and why it fixed itself.
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Old 12-25-2011, 06:03 PM   #10
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Help, 110 V from each leg but no 220 between legs


Two options explain your syptoms -

You have lost one leg !
The voltage you are measuring with the meter,
could well be a back feed voltage !

or

Both hots are coming from same phase/hot.
What has changed recently ?

Last edited by dmxtothemax; 12-25-2011 at 06:21 PM.
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Old 12-25-2011, 06:19 PM   #11
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Help, 110 V from each leg but no 220 between legs


not if his heater is currently working, it's not back feeding. it's an electric air handler, requires 240 volts for the electric heating elements and the blower to run simultaneously.
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Old 12-25-2011, 06:23 PM   #12
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Help, 110 V from each leg but no 220 between legs


Quote:
Originally Posted by petergun1 View Post
Let me thank everyone that replied. The zero voltage was measured at the air handler breaker. The panel breaker did show 220 volts, so I went back to the air handler breaker and removed two wires that were wired to the supply side of the breaker. These wires lead outside to the air conditioning unit. The heater now works and I will have to figure out what those wires supply in the next couple of days -- it's raining right now.

A little info: I live in a small southern Mississippi town where until four years ago building regulations were almost none existent. The process entailed paying ten dollars for the permit, no one ever followed up. Essentially you could do whatever you wanted. Who know what I will find when I open the side of the air conditioner.

Again, thanks for the quick and valuable replies.

That is your 240 volts to your condenser. You may have a single pole contactor in the condenser which means one leg is always drawing hot and could be the problem. You can change that contactor to a double pole so no hots are drawing unless cool is calling. You now have heating but no cooling.

The right way is they are supposed to be on individual breakers. Most likely the outside condenser on a double 30-50 amp and the inside air handler being a double 60.

You have on or two sets of breakers in the air handler? Might be a double 60 and a double 30.

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