How to test a thermostat with a multi meter

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How to test a thermostat with a multi meter

Postby kajaydA » Sun Feb 06, 2011 12:00 pm

I would like to know how to test a digital thermostat (new Honeywell programmable) with a multimeter at the furnace control board The control board is Honeywell TotalZone.

I have standard mult-meter and need to know where to put the leads and what settings. Also, is this signal in millivolts DC and what range?

So, when the thermostat should be calling for heat, what should the multi-meter read at the control board?

Thanks in advance,

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- How to test a thermostat with a multi meter

Postby 4ftBanger » Sun Feb 06, 2011 12:15 pm

Almost all conventional heating & cooling systems use a 24 volt AC control signal and most use a standard wiring (that is, the wiring terminals are typically marked R, W, Y, G and C).

There are points of high voltage on the board so if you aren't comfortable working with electricity.....

At the furnace control there should be approximately 24 volts measured between the R terminal and the C terminal. During a call for heat on a gas furnace there should be 24 volts between the W terminal and C terminal.
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