# Help, 110 V from each leg but no 220 between legs



## petergun1 (Dec 25, 2011)

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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## gregzoll (Dec 25, 2006)

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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## Daniel Holzman (Mar 10, 2009)

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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## gregzoll (Dec 25, 2006)

Daniel Holzman said:


> 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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## TarheelTerp (Jan 6, 2009)

petergun1 said:


> I measured the supply voltage to the breaker at the air handler ...


go back to the panel and check what you have there



> Any ideas?


something very fundamental is seriously out of whack.

hth


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## zappa (Nov 25, 2011)

petergun1 said:


> 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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## joed (Mar 13, 2005)

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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## petergun1 (Dec 25, 2011)

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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## zappa (Nov 25, 2011)

Sounds like the feed to the outdoor unit. I wonder what your original problem was and why it fixed itself. :huh:


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## dmxtothemax (Oct 26, 2010)

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 ?


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## Doc Holliday (Mar 12, 2011)

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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## Doc Holliday (Mar 12, 2011)

petergun1 said:


> 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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## AixNPanes (Jul 2, 2021)

Some additional information in case anyone comes here looking. Just had similar systems. A/C not working, Range and oven not heating but display working. The A/C thermostat had gone blank. I opened it and the batteries were all corroded. There was a trace on a circuit board that was also lifted and an adjacent contact was corroded. I pulled the panel off the main breaker panel and measured the voltage on the range breaker thinking I might have lost one breaker of the pair. Each leg measured over 100V to ground, but 0V between the legs. It didn't seem quite right but I didn't give it much thought as we've had a PLETHORA of maintenance problems the last few weeks. As I was trying to find info on debugging the range problems a neighbor called with similar issues!!! She mentioned the power company meter was blank. They just installed the new digital smart meters a couple of years ago. Sure enough 3 consecutive neighbors have blank power meters, the 3 running off a common distribution box in our yard. That means it has to be a power company problem. Hopefully these comments may save someone some grief.

I don't know how power distribution systems work, but it seems like maybe there was a problem in our distribution box and rather than just dropping a leg, they shifted the bad leg to the leg that was working. I guess that might be a reasonable failsafe. I'll probably never know.


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## joed (Mar 13, 2005)

10 year old thread no further comments needed.


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## Rope50 (3 mo ago)

Daniel Holzman said:


> 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?


I had same problem. I checked from breaker to dryer. I had 120v to ground or neutral on both legs and 0v from leg to leg at the dryer. I checked everything from breaker to dryer. 120v both legs to ground and o volts from leg to leg. After all it was bad breaker and I don`t know how. Changed breaker works fine.)


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## chandler48 (Jun 5, 2017)

See post #14. @Rope50 it is always best to start your own thread, describing your situation and probably referring to this thread as a back up.


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## AndyGump (Sep 26, 2010)

Both of your hot legs are probably on the same phase.

Andy.


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## chandler48 (Jun 5, 2017)

I believe Andy has it. Post a picture of your panel so we can see how it is connected


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