AC won't turn on unless fan switched turned to ON from AUTO

Discussion in 'HVAC' started by trefilov22, Jul 9, 2012.

  1. Jul 9, 2012 #1

    trefilov22

    trefilov22

    trefilov22

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    I currently rent out a home I own in IL and live in IN. The renter called and stated that they had to switch the thermostat from auto to on to cool down the house. Could this be a battery that is dying and not tripping a switch to turn the fan on? I couldn't tell you the last time I changed that battery, its probably 3-4 years old at least. That is just the first thing the came to mind.

    Any thoughts?
     
    Last edited: Jul 9, 2012
  2. Jul 12, 2012 #2

    lloyd

    lloyd

    lloyd

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    Yep definately could be. I ran across one very similar the other day. It's a bummer that a couple of aa batteries can hold the power of life in a whole hvac system.
     
  3. Jul 12, 2012 #3

    kok328

    kok328

    kok328

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    I'm thinking that the transformer would continue to power the thermostat and the batteries are just to maintain the programming in memory in the event of a power outage.
    Could be that the thermostat is bad but, only troubleshooting will reveal the problem.
     
  4. Jul 13, 2012 #4

    lloyd

    lloyd

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    The transformer can't power a thermostat unless it is a five wire configuration where a common wire has been brought from the transformer and connected to a "c" lug. In this case batteries would be optional and useless. Setting are stored in non volatile memory that needs no power.
    In a normal 4 wire config, the batteries run the thermostat. Red is power and every other wire an extension of that as the thermostat calls for it. Below is from a honeywell non programmable thermostat manual.


    1. Replace the batteries as soon as Replace
    Battery flashes in the display. The Replace Battery
    indicator flashes in the display two months before
    the batteries run down completely.
    2. Always use fresh AAA alkaline batteries. Nonalkaline
    batteries do not last as long and can leak,
    causing damage to the thermostat.
    3. Although the thermostat has a Replace Battery
    indicator, replace the batteries once per year to
    prevent the thermostat and heating/cooling system
    from shutting down due to a lack of battery power.
    NOTE: Replacing the batteries once a year also helps
    prevent battery leakage that can damage the
    thermostat.
    4. As a precaution, replace the batteries when leaving
    your home for more than a month to prevent your
    heating/cooling system from shutting down if the
    batteries run down completely.
     

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