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  1. #1
    Join Date
    Jul 2010
    Location
    Washington
    Posts
    70

    Default Low limit on Thermostat

    This forced air heat pump system had run on A/C all day and our 4:00pm inspection had the evening temperatures drop to 67 inside the home before I was inside to operate the unit. The thermostat's A/C setting didn't drop below 68 and so I didn't get it running.

    A few questions:
    1. What is the reason that a thermostat would limit the A/C setting to 68 degrees as the coolest setting?

    2. Does operation of the furnace's backup electrical coil (EM Heat setting) risk damage to the system in the way that quickly switching from cooling to heating or heating to cooling does?

    3. Where does the damage happen in this process? Along the way i've observed a rule of thumb that a system should rest for hours before switching modes. I've read thermostat user manuals that suggested that this timeframe was a few minutes. If this is the case i'd test heat pumps in both settings over the course of an inspection.

    Any comments much appreciated...

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  2. #2
    Join Date
    Mar 2007
    Location
    Orlando, FL
    Posts
    1,340

    Default Re: Low limit on Thermostat

    Many, or most, digital t stats have a pre-programed "spread" between heat & cool modes, likely 3 or 4 degrees. What was the heat temp set to that day?


  3. #3
    Join Date
    Jul 2010
    Location
    Washington
    Posts
    70

    Default Re: Low limit on Thermostat

    Cooling set at 68, Heating at 65.


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