How do Two-Stage Air Conditioner Units Work? - Ask the Expert Episode 219

Today's question comes from Sam. "Hey Dan. I had a two-stage air conditioner installed. Works great. What is the determining factor that causes the system to go from one stage to the other? Put another way, how does it know to switch? I'm certain the the installer didn't leave an HVAC fairy in my attic next to my air handler."

Oh, I wish there were HVAC fairies. That would be like the best thing ever.

Your two-stage air conditioner is going to basically run according to your thermostat. Let's say you set your thermostat on 70 degrees. Initially, when the system starts to cool, it's going to start your first stage. If it maintains the temperature, it will remain there. If it can't maintain, like if it stays around 72 or 73 degrees, then it kicks into that second stage to maintain the interior comfort.

There are some thermostats that do this by time. For example, the system may kick into the second stage if the temperature isn't cooled within 15 minutes.

If you have any questions, please leave them in the comments below!

4 comments (view/add)
  • Jason
    Posted on 7/1/2020

    Good stuff. I could watch more of this guy

  • howard
    Posted on 6/30/2020

    ok, so how should you program your thermostat to keep it in stage one. i have a thermostat that has 6 time cooling mode, if going from 76 to 72, i will start 4 hours before and start dropping the temp 1 degree per hour. will this keep it in stage one? i have a goodman 18 seer 2 stage heat pump with a propane backup. my thermostat is a sensi. what are your suggestions.

  • Kyle
    Kyle from Ingrams
    Posted on 7/1/2020

    Most 2 stage thermostats do not have the capability of eliminating stage 2. However, the signal wire for Y2 can be disconnected and that will prevent 2nd stage compressor operation. The programming you mention will most likely still activate 2nd stage occasionally since the differential for most thermostats is 1F. There are some thermostats that have a stage differential setting, but not many do.

  • Joe S. Sr.
    Joe S. Sr.
    Posted on 6/30/2020

    Dan, you’re watching too much Hallmark. But good video.

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