Compressor doesn't kick on with air handler?

[m32825]

I got an energy monitor and have been learning more about our usage patterns. I noticed something I don't understand with the heat pump.

We're running AC and normally I see the compressor and fan start up at the same time, then the compressor turns off, then a little while later the fan turns off. Sometimes the fan starts but the compressor doesn't. Then the compressor kicks in a few minutes later, sometimes for a very short period.

The first couple cycles in the attached graph look right to me, but the rest show what I'm describing. Is this normal behavior or a sign of some issue? Thanks!

-- Carl

 

[samss]

Do you have a programmable tstat? Maybe it's set to cycle the airhandler if the system hasn't ran for a certain amount of time, and while the airhandler is running the tstat senses enough change to kick in the compressor.

 

[justinjoyal]

HP waiting for time delay to be done.

Looks like your system is short cycling..

 

[fitter30]

Justinjoyal 1+ time delay in condenser and a other one in the stat a possibility also might be cycles an hour programmed in the stat. What is the brand of stat and model?

 

[m32825]

Honeywell TH8320R1003

None of the air quality/circulation features are enabled, though it is capable of that, good suggestion.

Yes, the time delay. That fits perfectly, the data was right there in front of me the whole time. Is there something I should change or is this an example where ignorance is bliss?

-- Carl

 

[fitter30]

This stat must have more computer power than Watson. Page 61 fig 84 look at circ 3, page 71 P+I control.

 

[m32825]

Investigated where the 10 minute delay was coming from. Found a "delay on break" timer set to 10 minutes inside the heat pump, see attached.

I also found that the factory default on cycles per hour is 6 for cooling and 9 for heating. Changed that to 4 each in hopes of getting fewer/longer cycles. Will see what happens tonight.

You are right fitter30, for sure this thing knows more calculus than I do. I'm reading up on circulation and P+I control so I can experiment with those next. Thanks for the suggestions!

-- Carl

 

[m32825]

OP with an update...

This has been a great exercise. After monitoring for a while I figured out that the thermostat location was causing the AC to short cycle during the night. The thermostat is located near the kitchen, and there's a big honking freezer nearby. When the freezer runs it heats the air around the thermostat and makes the AC kick on, but then because the whole house isn't warm the temperature drops as soon as the air starts to circulate.

Added a wireless remote thermostat that I can put wherever I want. I tried a couple different spots and currently have it near an inside wall in one of the bedrooms. Temperatures have been more consistent with this arrangement, no more freezing us out in the middle of the night. Sample run from last night below.

-- Carl

 

[greg_b]

Which monitor package are you running? Is it a direct monitor system, or are the loads learned?