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-   -   How is a thermostat tested? (https://www.askmehelpdesk.com/showthread.php?t=269591)

  • Oct 15, 2008, 06:17 AM
    gleasman
    How is a thermostat tested?
    Is there a way to test a home HVAC thermostat? Maybe with a multimeter? Thanks.
  • Oct 15, 2008, 06:29 AM
    KISS

    You could. It depends a lot on the type of stat. Powered, mercury, line etc.

    Mercury stats have to be level and at the same additude.

    You may have to provide battery or 24 VAC power to the stat.

    Since the thermostat is a collection of contact closures, for the most part. There are a few with indicating lights.

    These contact closures are from R, Rc or Rh to each terminal.

    If the stat is in the right mode, then the correct contact should close.

    In a simple stat with R, W, Y, and G, there will be closures between R and W, R & Y, R and W and R an G depending if there is a call for heat, call for cool or call for fan. A call for heat in a gas system does not cause a call for fan. A call for cool does.

    You have to know a fair bit on how a tstat operates to know what to check.

    Although a multimeter can likely tell you you have a bad stat, it may not tell you if you have a good one using resistance.

    Using a small load or a relay and measuring the voltage drop across the tstat contact will give you a better idea of tstat health.

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