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Old 12-26-2013, 11:19 AM   #1
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American standard freedom 90 common wire


I have been told that my Common "C" wire (blue) should be supplying 24V AC and I am only seeing 2-3 volts.

I have 2 units, 1 American Standard Freedom 90 and 1 Trane 85. Both supply the same power.

I was looking to install a new programable thermostat that requires 24 volts and have been told that my furnace should be supplying this to my thermostat via the "C" wire.

Any suggestions as to why both units would not supply 24 volts and why both units work just fine with the old non intelligent thermostats?

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Old 12-26-2013, 11:57 AM   #2
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American standard freedom 90 common wire


C /Common wire has no voltage and is the same as a white or neutral wire that you have with your 120 volt house wiring. you were told wrong. post a pic of the circuit board in the furnace. just hookup a #18 wire to the C wire on the terminal strip where the tstat wires attach and hook it up at the tstat and it should work. try stay away from cheap tstats made in China etc as the electronics are bad. Honeywell makes good ones and HDepot has them.

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Old 12-26-2013, 02:41 PM   #3
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American standard freedom 90 common wire


http://www.wifithermostat.com told me that if I connected the C to the G it would turn on the fan and since it did not that is the issue.

I researched all over the internet and figured that what I had already known and what you just stated was correct. Red is 24v and a volt meter R to C shows 24V AC.

So that would imply their thermostat is defective not the bad wiring. I will try a new one.

Thank you!
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Old 12-26-2013, 02:57 PM   #4
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American standard freedom 90 common wire


Per their website and documents

"Important! C wire is required and is the primary power source for your thermostat. Without a C wire, your thermostat will not power up."

funny if C is the Common/Ground their statement is totally wrong.... unless maybe in their world electricity is backwards.
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Old 12-26-2013, 04:26 PM   #5
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American standard freedom 90 common wire


Quote:
Originally Posted by hollorg View Post
Per their website and documents

"Important! C wire is required and is the primary power source for your thermostat. Without a C wire, your thermostat will not power up."

funny if C is the Common/Ground their statement is totally wrong.... unless maybe in their world electricity is backwards.
Their instructions are written by a "technical" writer. He tries to put into words. What an engineer describes. often, a lot is lost in the translation.

C is common. As all low voltage power must return to the transformer common terminal. Hence the letter designation C.
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Old 12-26-2013, 05:19 PM   #6
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American standard freedom 90 common wire


In order to have a power source C is needed is how it should be written.
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Last edited by yuri; 12-26-2013 at 05:21 PM.
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Old 12-26-2013, 06:48 PM   #7
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American standard freedom 90 common wire


the older stats worked on a feed backs to run the stat... the newer style with digital displays and more draws in VA need a constant 24V at the subbase when reading R to C......for those hooking up a newer stat calling for that C wire (hopfully you have a spare on that pull) if not the stat sits lit but with no action when calling the system in.....
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Old 12-27-2013, 05:54 AM   #8
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American standard freedom 90 common wire


They told me to test the common wire to attach it to Green/ Fan and the fan should turn on. If that is a troubleshooting method power would need to be in one of the 2 wires. Hence my confusion.

In one of the areas of my house we have zones and I had to do all the wiring because the HVAC tech had no idea how that worked. So I researched all of this and was completely confused when they were telling me this.

Everything you say makes sense. I guess the thermostat is dead. I will try to swap it to verify. I was also thinking of directly hooking it up to the power source. I would guess that would be Black to Red and White to Common as this is AC.

Thank you
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Old 12-27-2013, 07:09 AM   #9
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American standard freedom 90 common wire


if you have a control module within the furnace with R,Y,W abd G and C on it d the jumping down there...R to G fan...NOTE shut the CB off for the outside condenser if it is cold out could damage the compressor with this jump...R to Y condenser and R to W heat.to test the stat wires from the stat to the control module or just into the furnace do the same jumps if a wire is "fagazy"...DO NOT JUMP R TO C ...anyplace that is a dead short on the TR and will burn it out if it isn't fused .G,Y and W are actually the C side of the TR but controlling the loads that bring on each item when jumping...does your subbase have a C terminal to land up there?so you can read 24Vs on the subbase with the stat removed as it should be?

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