Question on AC condenser unit

lesliewDecember 19, 2010

My home has three phase wiring, and last year, when I had to replace a five ton AC condenser, the AC company told me I either had to use a three phase unit (commercial, and more expensive), or they would have to redo the wiring. I told them I would prefer not to jury rig the wiring, and wound up spending almost five thousand dollars for the unit. I had a smaller unit replaced this year, by another company, which turned out to be single phase. When I mentioned my relief, and told the guy the story about the larger unit, he looked at it, and said it was single phase. I went back to my contract, and checked out what was written, and it definitely said three phase, thirteen seer. I checked the model number online, and found it to be a single phase, eleven seer unit. Obviously the installer took me for a ride, but my main question is - what did they have to do to the wiring to use a single phase unit, and should I be concerned about the wiring, as wlel as about the fraud involved?

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Probably only had to cap the unused third phase wire.

    Bookmark   December 19, 2010 at 10:08PM
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If you wire across two phases of a 3-phase circuit, won't the resulting waveform be a bit whacky? The two phases are 120* apart, not 180*, so won't the voltage be non-steady?

    Bookmark   December 20, 2010 at 5:14PM
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Using two legs of a three-phase system is simply single-phase. there is no problem with the voltage.

Two legs of a 120/208V 3-phase system is 208V.

    Bookmark   December 20, 2010 at 7:50PM
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If you wire across 2 phases, you'll typically have a "steady" 208V. Whether or not the AC will run on that is another question. Unless designed for that voltage, my guess is that the lifespan will be shortened considerably.

    Bookmark   December 20, 2010 at 7:51PM
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A delta service was once quite popular for larger residential HVAC installs. If it is a 120/240 delta service, a wire nut cap on the "wild leg" makes it essentially the same as 120/240 single phase. Since the circuit capacity will be lower that way, my advice is to find a reputable HVAC company to look over the install. Then take that information and your contract to a good, mean lawyer.

Fraud seems fairly common in the HVAC trade, when I had a unit installed, a 2 ton condenser was "accidentally" placed in the carton marked as 2.5 ton.

    Bookmark   December 20, 2010 at 9:27PM
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