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volan · Jun 20, 2007, 04:21 PM

I am considering purchasing a Honeywell W8665A remote control thermostat. I have the wiring diagram and I am a bit confused. I'm hoping someone can help me.

My current thermostat attached to the wall has the following wires available:
Y, G, R, W.

The manual for the W8665A states that C must be connected, but I have no 'C'. Apparently the C is a common coming off the transformer.

Am I out of luck or is there a way around it?

hvacservicetech_07 · Jun 20, 2007, 05:57 PM

I'm pretty sure you'll need a common to power that thermostat, if all you have is four wires sticking out of the wall, simply pull a 5 ct cable and hook the common up on the furnace, this may be pretty easy if they didn't attach the wire to a stud inside the wall, just connect the new wire and old and pull it down through the wall.

volan · Jun 20, 2007, 09:20 PM

Thank you. I'm not confident pulling a cable from the basement up to the 2nd floor of my house. Perhaps I'll consider professional help.

But at lease now I know that I need the 'C' wire and I won't rush into buying the unit until I know what I'm going to do.

Thanks again.

hvacservicetech_07 · Jun 20, 2007, 09:22 PM

Is there a reason that you want that thermostat? There are some nice stats on the market that would work just fine, and they have a nice look.

hvacservicetech_07 · Jun 20, 2007, 09:28 PM

Keep in mind, it wouldn't cost you very much to call in a pro to pull a new wire and install the thermostat, your talking an hour labor or less.

volan · Jun 21, 2007, 07:09 AM

Originally Posted by hvacservicetech_07

Is there a reason that you want that thermostat? There are some nice stats on the market that would work just fine, and they have a nice look.

The current thermostat is located in a hallway in front of a big picture window so the temperature reading is not what the temperature in the rooms are. That's why I wanted a remote control thermostat. That way I can put the sensor in one of the rooms and the temperature control will be more accurate.

volan · Jun 21, 2007, 07:11 AM

Originally Posted by hvacservicetech_07

Keep in mind, it wouldn't cost you very much to call in a pro to pull a new wire and install the thermostat, your talking an hour labor or less.

Only an hour? I'll check into it. Thanks.

biggsie · Jun 21, 2007, 08:58 AM

The transformer supplies 24 vac (C is common for 3 relays -- cooling --heating -- fan and common for thermostat power Fig.2 The other leg is R which provides
Power to thermostat, and is jumpered to RZ terminal...

http://customer.honeywell.com/techli...0s/69-1630.pdf

Inside wall would be good location for thermostat Maybe a new run would work...

volan · Jun 21, 2007, 09:08 AM

Yes, I plan to put the thermostat in one of the rooms away from direct sunlight

tazdec · Jun 21, 2007, 03:14 PM

Originally Posted by volan

I am considering purchasing a Honeywell W8665A remote control thermostat. I have the wiring diagram and I am a bit confused. I'm hoping someone can help me.

My current thermostat attached to the wall has the following wires available:
Y, G, R, W.

The manual for the W8665A states that C must be connected, but I have no 'C'. Apparantly the C is a common coming off the transformer.

Am I out of luck or is there a way around it?

See if your stat reads power stealing if not you need a common to the stat see if you have a extra wire in your stat wire if you do you can hook up c at the unit and the c at the stat

volan · Jun 21, 2007, 03:29 PM

Originally Posted by tazdec

see if your stat reads power stealing if not you need a common to the stat see if you have a extra wire in your stat wire if you do you can hook up c at the unit and the c at the stat

Thanks for your post.

I don't actually have the thermostat yet. I'm just doing my due diligence prior to purchasing it. I find that doing work upfront results in less frustration afterwards.

The only wires I have at the T-stat are those that I have mentioned. There do not appear to be any spare wires that I can see.