# 3 phase compressor



## Joe Robert (Dec 21, 2017)

This may be more of an hvac question but I figured some of you may be able to answer it.

Last year I installed three 208 heat pumps at a dentist’s office, the circuits were all 240 so we used stepdown transformers at all three units. The office has been vacant for about 4 months now and somewhere during that time some contractors changed the entire building to a 208 service without consulting us.

After bypassing the transformers at all three units, the two smaller ones run fine, but at the largest of the three the compressor will not run. All three units had power going to the compressors at the incorrect voltage for an unknown amount of time, and would not start because of that.

I’ve checked everything in the largest unit, capacitor, relays, safeties, start and run windings resistance; all good. Question is could the lower voltage have caused damage to the compressor, since it was energized but wouldn’t run? And if so why am I still getting good resistance from both windings?


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## glen1971 (Oct 10, 2012)

Joe Robert said:


> This may be more of an hvac question but I figured some of you may be able to answer it.
> 
> Last year I installed three 208 heat pumps at a dentist’s office, the circuits were all 240 so we used stepdown transformers at all three units. The office has been vacant for about 4 months now and somewhere during that time some contractors changed the entire building to a 208 service without consulting us.
> 
> ...


Did the line and control fuses check out? Overloads? Are the voltages at the compressor correct now?


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## Helmut (May 7, 2014)

Joe Robert said:


> All three units had power going to the compressors at the incorrect voltage for an unknown amount of time, and would not start because of that.
> 
> I’ve checked everything in the largest unit, capacitor, relays, safeties, start and run windings resistance; all good. Question is could the lower voltage have caused damage to the compressor, since it was energized but wouldn’t run? And if so why am I still getting good resistance from both windings?
> 
> ...


Maybe they screwed up the phasing when they put in the new service, and something ran backwards for a while.


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## frenchelectrican (Mar 15, 2007)

Helmut said:


> Maybe they screwed up the phasing when they put in the new service, and something ran backwards for a while.


This is one of the most common error when someone change the service voltage like going from 240 volts delta to 208 volts Wye.

that why anytime you change the service you have to check the phase rotation before the power is cut off and after the new service is hook up then check the rotation again to make sure it is in correct rotation.

same thing going from uility side or shore power source to generator source.

some of the A/C compressor do have phase reverse rotation protection on it. so if that happend it will prevent from damaged it.

The piston compressors are not too bad but oil pump ya., but scroll types ya it is noticeable.,

To OP did you try change the phase conductor around yet ? typically any two phase swap around useally do the trick.


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## MechanicalDVR (Dec 29, 2007)

frenchelectrican said:


> This is one of the most common error when someone change the service voltage like going from 240 volts delta to 208 volts Wye.
> 
> that why anytime you change the service you have to check the phase rotation before the power is cut off and after the new service is hook up then check the rotation again to make sure it is in correct rotation.
> 
> ...



Improper phasing will kill a scroll in no time flat.


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## MechanicalDVR (Dec 29, 2007)

Joe Robert said:


> This may be more of an hvac question but I figured some of you may be able to answer it.
> 
> Last year I installed three 208 heat pumps at a dentist’s office, the circuits were all 240 so we used stepdown transformers at all three units. The office has been vacant for about 4 months now and somewhere during that time some contractors changed the entire building to a 208 service without consulting us.
> 
> ...


There shouldn't be a cap on a 3 phase compressor.

Try switching the phasing around and see if it starts.


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## telsa (May 22, 2015)

MechanicalDVR said:


> Improper phasing will kill a scroll in no time flat.


Running them backwards will do that too. :surprise:


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## MechanicalDVR (Dec 29, 2007)

telsa said:


> Running them backwards will do that too. :surprise:


That is what I meant by improper phasing.

Running in the correct direction they sound like a washing machine, running in the opposite direction they sound like a fine tuned motor full of gravel.


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## Joe Robert (Dec 21, 2017)

glen1971 said:


> Did the line and control fuses check out? Overloads? Are the voltages at the compressor correct now?




All fuses are good and voltages are correct, even switched the control board from another unit, same ****.

And I apologize I should have clarified these are single phase units, no three phase here so rotation isn’t of concern.


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## John Valdes (May 17, 2007)

You're a lineman? But you are in the HVAC trade? And you work for the POCO?
Which one is it?
And you had 3, 208 volt, 3 phase compressors that were not rated for 240 volts as well?
Its seems its always been the opposite for for me. 240 volt equipment on 208 volt nominal.


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## frenchelectrican (Mar 15, 2007)

Joe Robert said:


> All fuses are good and voltages are correct, even switched the control board from another unit, same ****.
> 
> And I apologize I should have clarified these are single phase units, no three phase here so rotation isn’t of concern.
> 
> ...


If that was the case if single phase unit sometime you will need a hard start kit that will actually start the single phase compressor better on 208 volts system which I have ran into from time to time.


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## Joe Robert (Dec 21, 2017)

John Valdes said:


> You're a lineman? But you are in the HVAC trade? And you work for the POCO?
> Which one is it?
> And you had 3, 208 volt, 3 phase compressors that were not rated for 240 volts as well?
> Its seems its always been the opposite for for me. 240 volt equipment on 208 volt nominal.




I’m four months away from graduating from the POCO’s two year lineman school, hired on right after. I do HVAC nights and weekends to pay the bills.


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## Joe Robert (Dec 21, 2017)

frenchelectrican said:


> If that was the case if single phase unit sometime you will need a hard start kit that will actually start the single phase compressor better on 208 volts system which I have ran into from time to time.




I’m gonna give this tomorrow morning 


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## sbrn33 (Mar 15, 2007)

Joe Robert said:


> I’m gonna give this tomorrow morning
> 
> 
> Sent from my iPhone using Tapatalk


You just said they were 3 phase???


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## Joe Robert (Dec 21, 2017)

sbrn33 said:


> You just said they were 3 phase???




Yep, I was already a few deep when I posted this yesterday. No idea why I said 3 phase compressor in the title, I’m ******ed haha

And the hard start kit did the trick, thanks French and everyone else who helped this coat hanger dodger


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## frenchelectrican (Mar 15, 2007)

Joe Robert said:


> Yep, I was already a few deep when I posted this yesterday. No idea why I said 3 phase compressor in the title, I’m ******ed haha
> 
> And the hard start kit did the trick, thanks French and everyone else who helped this coat hanger dodger


You are more than welcome on this one.


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