# INstalling Honeywell RTH6500WF thermostat



## Bob Sanders (Nov 10, 2013)

It's actually supposed to be 24vac. There isn't a big difference there but maybe it's enough to cause problems.


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## Jerbeak (Nov 23, 2013)

*Thanks for the reply*

I will pursue that.


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## beenthere (Oct 11, 2008)

Moved to HVAC forum.


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## HVAC1000 (Dec 12, 2012)

Jerbeak said:


> The new thermostat is blank, like no power. I measure about 20v ac between C-R and no voltage between C and G, W, or Y. I know C is the power. What could the problem be?


C is not power, R is power. C is common to the not hot side of transformer. Check again with R to all terminals


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## Jerbeak (Nov 23, 2013)

*Installing Honeywell RTH 6500 WF thermostat*

I measured R to C,G,W and Y. There is only 1.0 vac between R and each of the other pins individually. The old thermostat worked fine. All I did was put in the new Honeywell thermostat so I could use WI-FI control. What could I have done to lose the 24 VAC? I am measuring the voltage with all wires disconnected, i.e. the thermostat is not hooked up.


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## HVAC1000 (Dec 12, 2012)

Jerbeak said:


> I measured R to C,G,W and Y. There is only 1.0 vac between R and each of the other pins individually. The old thermostat worked fine. All I did was put in the new Honeywell thermostat so I could use WI-FI control. What could I have done to lose the 24 VAC? I am measuring the voltage with all wires disconnected, i.e. the thermostat is not hooked up.


Go down to furnace and look for a little 3 or 5 amp fuse on the control board. It looks like an automotive on. If its blown replace it and check back, but first make sure none of the t-stat wires are touching though. Screw them all in thermostat base but leave stat off then replace fuse and test. Make sure furnace breaker is on, main switch is on and furnace door is in place otherwise you won't get a reading all day.


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## Jerbeak (Nov 23, 2013)

*Honeywell RTH 6500 WF thermostat*

Thanks for the info. I was wondering about a fuse or breaker. I live in Arizona and the furnace is in the attic in the homes down here. I am 72 yrs old and my shoulders (rotator cuff problem) are not strong enough to lift myself from my ladder up into the attic. I am going to see if my neighbor has a taller ladder.


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## HVAC1000 (Dec 12, 2012)

Jerbeak said:


> Thanks for the info. I was wondering about a fuse or breaker. I live in Arizona and the furnace is in the attic in the homes down here. I am 72 yrs old and my shoulders (rotator cuff problem) are not strong enough to lift myself from my ladder up into the attic. I am going to see if my neighbor has a taller ladder.


I'd come do it if its warm down there haha


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## Jerbeak (Nov 23, 2013)

*Honeywell RTH 6500WF thermostat*

Was in the 70's until last Friday. 2.6 inches of rain Fri & Sat. Now in the mid 60's, still not that bad.


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## HVAC1000 (Dec 12, 2012)

Jerbeak said:


> Was in the 70's until last Friday. 2.6 inches of rain Fri & Sat. Now in the mid 60's, still not that bad.


very nice it's cold and snowy here. Did u hear about all the rain and flooding we go a few months ago? Pretty much cut the state in half. I was on the wrong from home that day and it took me 3 hours to go 10 miles across two flooding rivers


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## Jerbeak (Nov 23, 2013)

*Honeywell thermostat*

I could not find the fuse in the furnace in my attic. I knew there had to be one. I had to call a heating/ac company. I have used them before. He found the blown fuse right away. He said it was not easy to spot. All fixed.


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## dgwright99 (Dec 8, 2013)

*"C" is not Com on RTH6500WF*

The install guide is clear that for the RTH6500WF, "C" is for powering the unit, not a common. They give a link to wifithermostat.com/videos which has a video describing how to use the "G" wire if you don't have an appropriate supply for "C" on your furnace - but of course if you do that you can't run the fan independently of heating/cooling.

I only have heat, no cooling, but the control board of my furnace (Bryant 310AAV) has a Y terminal, and so I figured I could use that for the "C" terminal on the 'stat, but I wanted to get some opinions here before I did that. I'm a EE, but pretty much all I know about HVAC I learned researching how to fit these 'stats - I've wired up 'stats in the past, but it was always an easy direct substitution.

Thoughts ?


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## beenthere (Oct 11, 2008)

dgwright99 said:


> The install guide is clear that for the RTH6500WF, "C" is for powering the unit, not a common. They give a link to wifithermostat.com/videos which has a video describing how to use the "G" wire if you don't have an appropriate supply for "C" on your furnace - but of course if you do that you can't run the fan independently of heating/cooling.
> 
> I only have heat, no cooling, but the control board of my furnace (Bryant 310AAV) has a Y terminal, and so I figured I could use that for the "C" terminal on the 'stat, but I wanted to get some opinions here before I did that. I'm a EE, but pretty much all I know about HVAC I learned researching how to fit these 'stats - I've wired up 'stats in the past, but it was always an easy direct substitution.
> 
> Thoughts ?


C is common, not power. If you don't have a common, then the power can't return to its source. R/RC/RH is power.

You must connect to the C/common of the furnace, Y won't work. Look for the common of the transformer, if there is no common on the furnace board.


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## hvactech126 (Nov 11, 2010)

DGWRIGHT99, As an EE, as you state, then you should know how ac voltage works. In order to power a load it must be a complete circuit. R is hot and C is common off the transformer. Y on older furnaces was a dummy terminal and had no bearing on anything in the furnace. Y on a late model furnace is functional in that when a G and Y signal is present it will increase the blower speed Vs. a G only signal will cause the blower to run at a slower speed. No doubt your furnace has a C terminal.... why would you not use it?


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