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Question on AC condenser unit

Posted by lesliew (My Page) on
Sun, Dec 19, 10 at 21:13

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?


Follow-Up Postings:

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RE: Question on AC condenser unit

Probably only had to cap the unused third phase wire.


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RE: Question on AC condenser unit

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?


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RE: Question on AC condenser unit

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.


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RE: Question on AC condenser unit

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.


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RE: Question on AC condenser unit

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.


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