Missing Y wire?

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Old 11-29-16, 06:49 PM
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Missing Y wire?

OK So like so many people I am trying to rig up a thermostat without a C wire.

I am instructed that after switching G to C I am to then jump Y to G.

The problem is that my furnace does not have a Y wire header even although somehow the Y wire of my thermostat is indeed hooked up to something...

Furnace

Thermostat

BTW Just for full disclosure it also does not have a C wire header, however it does have a pad on the back where the C header would go so I soldered a jumper wire to it that I affixed to the G cable going to the thermostat...

If this is a no no then please let me know...

C Wire header

Thanks for any help or suggestions!

BTW there are more pictures here if any other angles help

HVAC - Album on Imgur
 
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Old 11-29-16, 07:56 PM
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No need to solder on to the board. You can use the blue wire/side of the transformer or any convenient screw in the metal frame. Actually.... the blue in the picture below is common. It should connect to one of the A/C condensor wires. The other wire from the A/C condensor goes to yellow.

Here's the installation for that board..... shows schematic and ground/common.
icm controls/ProdImages/ig_LII318-2.pdf

I looked over your pics. I found this one. One cable is the stat and one is the outside condensor. This is the location of the yellow wire you are looking for BUT I see spare wires there. Are you sure you don't have a spare to the stat that is just cut off. (like blue)

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Old 11-30-16, 12:29 PM
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Wow I don't know how I didn't pick up on that...

At the thermostat wire is tucked back in the wall and wrapped around the shielding so I didn't see it and assumed it was just a 4 wire.

Oddly about half way down the lost the cable is cut and spliced for no apparent reason the blue is cut again



So it looks like I fish the blue out from the wall, connect the cut blue in the pic above I then have a 5 wire ready to go and can use blue as common?

So just need to figure out where to wire into for the com then?

I addd a few pics to the album -

Namely despite the board saying it's a B18099-10 it doesn't quite match the layout of the one shown. The one I have is this one

CONTROL BOARD 1012-932 B18099-10 | eBay

On the schematic you linked it points to one of the neutrals as being COM, however my neutrals are not laid out in the same way...

On my board (right next to the 3AM fuse) there is a spot in the area 24VAC
that is labeled COM



So it looks like my options are find the blue in the bundle you linked to (which I am a little weary off because the last time I took apart a bundle like that was behind a bathroom light and that got messy fast) - use the blue off the transformer (which I don't recall seeing a blue off it but I can check) or tapping off a com on the control board somewhere (which if so and the one labeled com on my board is really a com then that's pretty easy)?

Thanks for your help on this!
 
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Old 11-30-16, 01:24 PM
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Refer to the picture in post 2. Do you see that blue wire ?
That is your common connection.
If that is not in a handy location.... any metal screw on the furnace as the common side of the transformer on that furnace is connected to the metal chassis.
 
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Old 11-30-16, 01:42 PM
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Just to clarify you mean the big fat blue wire, not the tiny one that is wrapped around the shielding?

So unwarp the tiny blue wire from around the shielding, patch it in to the big fat blue wire, make sure that goes back to the thermostat and hook it up to C on the thermostat?

Also just for my edification the common wire carries 24v right? If it's connected to the chassis of the furnace does that mean the whole furnace is hot with 24 volts?

Thanks again for your help! If I got the blue wire thing correct that will make life so much easier!
 
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Old 11-30-16, 02:47 PM
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To clarify this is what am planning to do:

 
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Old 11-30-16, 02:57 PM
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I've discussed it several times. You should see another wire connected to that fat blue wire that goes to your outside A/C condensor. The other wire in that same cable connects to the Yellow wire.

That blue wire is connected to chassis if you follow it far enough.
You can combine your small blue wire with the large blue wire and whatever color goes to the condensor.
 
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Old 11-30-16, 03:06 PM
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Thanks for the clarification!

Sorry to be so pedantic about the details, had a bit of a scare as I wired something wrong on the first try and though I had blown the control board. It just blew the fuse but the thought of being out a heater in December kind of makes you want to triple check.

Appreciate the help!
 
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Old 12-01-16, 11:37 AM
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Just wanted to say thanks again!

Tracked the wiring back (it's a mess the last home owner was pretty handy all over the place) but mostly what you said was spot on and it's all hooked up. MUCH easier than the no c wire installation would have been.

Really appreciate it!
 
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