# CPH - Compressor Cycle Rate



## OscarNelsen (Mar 1, 2011)

I understand that setting the thermostat CPH to 3, yields 3 10 minute on/10 minute off cycles per hour.
My heat pump has a 2 stage compressor and the thermostat has CPH control for both stages. Why would you set Stage 1 to a different CPH from the Stage 2 compressor?


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## hvactech126 (Nov 11, 2010)

you would not.... both should be cph of 3


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## OscarNelsen (Mar 1, 2011)

Thanks for your response. I have no intention of changing these settings, but want to learn. I have installed a couple of programmables, but never on a 2 stage system. Why are there separate CPH controls for the compressor stages?


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## beenthere (Oct 11, 2008)

OscarNelsen said:


> Thanks for your response. I have no intention of changing these settings, but want to learn. I have installed a couple of programmables, but never on a 2 stage system. Why are there separate CPH controls for the compressor stages?


Because it changes how tight the temp control is. Some people like the system to shut off even at higher outdoor temps. Some people prefer the greater comfort of a unit that is running longer during the mid to 80% of design condition temp days of the summer.

A CPH setting of 3 doesn't mean it will run 3 10 minute on 10 minute off cycles per hour all the time. That is just what it will attemp and is only accurate at 50% load.


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## OscarNelsen (Mar 1, 2011)

Thanks. I realize that what I am learnig most is the less I know.


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## beenthere (Oct 11, 2008)

We all learn that there is always more to learn.


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