alfredog83: C wire for new thermostat

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Old 10-16-12, 09:41 PM
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alfredog83: C wire for new thermostat

Hello, again. It seems I keep coming back here to bother you guys with my troubles :/

I am replacing a faulty RiteTemp thermostat with a new Filtrete 3M-50. Upon removal of the existing unit, I found Y, G, R, and W wires. I thought myself lucky when I noticed an unused blue wire wrapped around the sheath, and figured I'd use it as a C wire, which I need for the WiFi module on the new unit.

Back on the furnace, however, I found no neatly organized terminal block with labeled wires, but rather a bunch of loose wires connected with wire nuts. The blue wire was wrapped the same way on this end, but I had no idea where to connect it.

I then noticed an unused purple wire coming from the handler. I thought I might get lucky and have that power the C terminal, so I used a wire nut to splice the blue to the purple. I'm a bit apprehensive about the whole thing though, so I've yet to connect the other end back on the thermostat for fear of causing irreparable damage.

Any idea what this purple wire is meant for, and would I be able to use it for my intended purposes? If not, is there a way for me to conjure up a C wire connection with the existing wiring?

Thank you guys for all your advice. Your help is more valuable than you can imagine.
 
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Old 10-16-12, 11:01 PM
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24vac common is the brown wire from the transformer shown on the right side of your picture. (not the brown capacitor wires)

It is next to the red 24VAC wire on the transformer.


Purple is electric heat strip.
 
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Old 10-16-12, 11:02 PM
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Your picture of the wiring diagram is too fuzzy for me to really be certain but I'm pretty sure that violet wire is incorrect. You CAN just connect the blue thermostat wire to the chassis and it will be correct for the thermostat C connection.
 
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Old 10-16-12, 11:56 PM
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24vac common is the brown wire from the transformer shown on the right side of your picture.
That brown is connected to a yellow wire, which is not connected to any terminal on the thermostat but rather some other mystery wire back at the receptacle. There is another black wire from elsewhere connected to the thermostat's Y terminal. Does that change things at all?
You CAN just connect the blue thermostat wire to the chassis and it will be correct for the thermostat C connection.
The diagram shows the brown wire Houston mentioned being connected to a GND screw. Is this why connecting the blue thermostat wire to the chassis would result in a correct connection?
 
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Old 10-17-12, 12:39 AM
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The diagram shows the brown wire Houston mentioned being connected to a GND screw. Is this why connecting the blue thermostat wire to the chassis would result in a correct connection?
Yes, that is the reason. jhiogyufgio;
 
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Old 10-17-12, 12:43 AM
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According to the schematic you gave us, the brown wire which comes from the 24vac transformer connects directly to ground (cabinet). In your photo I see the yellow thermostat wire going to the brown. That would seem to suggest that you have C at your t'stat location. In your last post you talk about receptacle. You've lost me there.
 
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Old 10-17-12, 06:34 AM
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In your last post you talk about receptacle. You've lost me there.
Sorry, the wording in that post is a bit confusing. What I meant is that back at the thermostat location, that yellow wire is connected to another wire rather than one of the t'stat terminals, and back out into the conduit. If I'm reading the schematic correctly, this seems to be going to the OD unit.
 
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Old 10-17-12, 08:38 AM
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Ok......so what's the problem ? The yellow wire is common and arrives at the back of the thermostat. If you want to use the blue wire also as a common connect it together with the yellow at the transformer location.
 
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Old 10-17-12, 08:45 AM
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Ok......so what's the problem ? The yellow wire is common and arrives at the back of the thermostat. If you want to use the blue wire also as a common connect it together with the yellow at the transformer location.
I suppose I just wanted to make sure that tapping into it wouldn't cause any problems elsewhere. Thanks for your help, guys!
 
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