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jmscp32

join:2014-04-07
Fall River, MA

[HVAC] Thermostat C wire on Honeywell RET97B5D Wireless


Thermostat

Schematic for the AC /Heat control
I purchased a Honeywell RET97B5D thermostat and i have a problem with the lack of the C" wire. Currently my thermostat has 4 wires. I measured between RH (red) and the each of the other wires and i measure about 29 vots AC. (Based on the 29, i am not sure if i can use any of these wires as the C wire.

I checked my heat and AC control and i noticed that the C terminal is hooked up to the condenser so i can not do who Honeywell recommends which is to use the G (green) as the future C.
I currently have 2 zones and i would like to the replace the current thermostats with wifi Honeywell RET97B5D
can someone help me in guiding me what to do with the missing C wire?
Thanks
John Medeiros

jmscp32

join:2014-04-07
Fall River, MA


AC_Heat control center
I forgot to add a picture of the AC/Heat wire terminations


Tex
Premium
join:2012-10-20
kudos:2

»Re: [HVAC] Connecting C wire without C terminal for wifi thermostat


iknow_t

join:2012-05-03
reply to jmscp32

I've seen a few posts like this, is this a new standard, dropping the "C" wire? a device doing that should give instructions on what to do..



jack b
Gone Fishing
Premium,MVM
join:2000-09-08
Cape Cod
kudos:1
reply to jmscp32

Doing the following will eliminate manual fan control capabilities through the thermostat.

You will be using the GREEN wire as your C in the new thermostat. Nothing will go on the G terminal in the thermostat.

Turn off the power supply to the furnace.
On the furnace terminal board remove the green wire from G and put it on C (with the white condenser wire)

Take a short piece of wire and jump terminals Y to G leaving the red and blue wires on Y.

For neatness I would make all wire splices using a wirenut and only have a single conductor under each screw terminal.

Done.
--
~Help Find a Cure for Cancer~
~Proud Member of Team Discovery ~



Tex
Premium
join:2012-10-20
kudos:2
reply to iknow_t

said by iknow_t:

I've seen a few posts like this, is this a new standard, dropping the "C" wire? a device doing that should give instructions on what to do..

There are plenty of instructions out there.

»www.google.com/search?client=saf···oe=UTF-8

And, Honeywell has instructions, too.

»youtu.be/jniws7wqeY4

kes601

join:2007-04-14
Virginia Beach, VA
kudos:2

1 recommendation

reply to jmscp32

There is a way to add a C wire with just a regular power outlet. I have not tried this, but was researching options after my Nest was not compatible with a new HVAC system I had installed. Was considering going with a Honeywell but decided to just stick with the Talking Thermostat that the HVAC company installed.

»www.amazon.com/dp/B0071IWJ7G/ref···IM&psc=1


garys_2k
Premium
join:2004-05-07
Farmington, MI
reply to jmscp32

Do you have any spare wires available in your current thermostat wire? If so, the C wire at the furnace end is any of the yellow wires connected to either of the two relays.



jack b
Gone Fishing
Premium,MVM
join:2000-09-08
Cape Cod
kudos:1
reply to Tex

These types of online instructions can be helpful for those with some HVAC wiring knowledge, but the uninitiated invariably only see a jumble of wires no matter what.
Many will want to try to do this work on their own and we get those guys/gals asking for help with their personal rats nest, since each one is a little different.
--
~Help Find a Cure for Cancer~
~Proud Member of Team Discovery ~



nunya
Premium,MVM
join:2000-12-23
O Fallon, MO
kudos:12
Reviews:
·Charter
·voip.ms
·surpasshosting

3 recommendations

reply to jmscp32

I can't believe that relinquishing fan control has become an acceptable solution just to install a fancy thermostat. I would be 100% unwilling to settle for such a hoakey solution.

Thermostat companies should be ashamed at providing such a ridiculous "solution" just to keep people from returning their over-priced product. Why don't they incorporate a multiplex solution into the thermostat? Why don't they put a plain English notice on the box that it will require a 5 wire cable?

Run a new t-stat wire or buy a thermostat wire multiplexer.
--
If someone refers to herself / himself as a "guru", they probably aren't.



Jack_in_VA
Premium
join:2007-11-26
North, VA
kudos:1
Reviews:
·Millenicom

I agree 100 percent. The fan option is to valuable to give up just for an overpriced fancy thermostat. When I upgraded my Heatpump system 2 years ago I had them change out my digital programmable thermostat and install a plain digital one. We never used the programmable as we just keep the same temp all the time.

However sometimes we do run the fan on manual mode and to not have that would be a problem.



SolvietSteve

@bell.ca

there is a simple solution but people seem to be too lazy to do this, its called pulling a new wire through. if your gonna wanna use a high end thermostat, u might as well pull an 18-5 or better yet 18-8 wire, your wire looks too inadequate for thermostat, it looks kinda thin.

-Solviet


TheSMJ

join:2009-08-19
Farmington, MI
reply to jmscp32

The Nest can run off of a 4 wire system without a C wire on most furnaces - they charge their battery whenever the fan is powered on.

Otherwise, you're either running a new cable with enough leads for a C wire from the furnace, running a 24V AC adapter's output to the thermostat, or using one of those add-a-wire adapters along with your existing wiring.

»www.amazon.com/Venstar-Add-A-Wir···013LVDQA


garys_2k
Premium
join:2004-05-07
Farmington, MI

Looking at the wiring diagrams it appears that Venstar unit also requires a C connection at the air handler end. It can convert a 4 wire system to 5 wires, but does need that C connection.


TheSMJ

join:2009-08-19
Farmington, MI

It looks like he has a C terminal on the air controller based on the photo. Why couldn't he use that?


garys_2k
Premium
join:2004-05-07
Farmington, MI

The OP can, for sure. Not everyone has a C terminal in the air handler, though, so for them the wire multiplexer would still be a challenge to use.



solvietunion

@bell.ca

just run the new wire


garys_2k
Premium
join:2004-05-07
Farmington, MI

said by solvietunion :

just run the new wire

Often easier said than done. The old wire may be stapled in place, it may have intermediate splices, etc. The multiplexer eliminates the need to deal with that.


SolvietSteve

@bell.ca

multi plexers can fail, new wire runs don't.
you decide

-Solviet



Tex
Premium
join:2012-10-20
kudos:2
reply to jack b

said by jack b:

These types of online instructions can be helpful for those with some HVAC wiring knowledge, but the uninitiated invariably only see a jumble of wires no matter what.
Many will want to try to do this work on their own and we get those guys/gals asking for help with their personal rats nest, since each one is a little different.

Let's just agree to disagree and leave it at that, okay?

jmscp32

join:2014-04-07
Fall River, MA
reply to jmscp32

Thanks to all that have provided input. So far, i followed Honeywell recommendations which is (at the thermostat ..G goes to C & @ the furnace ,,g-c and the jumper)., but it doesn't fully work. Somehow the heat works but the AC only stays on for a couple minutes and then it shuts off. It appears that the voltage isn't strong enough.
If am run the 5 wire conductor, where does the 5 wires go at the furnace? I am getting ready to undo what i did, please advise if you can
Thanks
John



Jack_in_VA
Premium
join:2007-11-26
North, VA
kudos:1

Sounds like the AHU Fan is not working. That will cause the outdoor unit to shut down on safeties.


jmscp32

join:2014-04-07
Fall River, MA

Thanks, do you know why and what i can do?


jmscp32

join:2014-04-07
Fall River, MA
reply to SolvietSteve

i can pull the wire, but can you tell me how to terminate the wire at the furnace and at the thermostat?



Jack_in_VA
Premium
join:2007-11-26
North, VA
kudos:1
reply to jmscp32

Probably your best option is put it back the way it was and pull the new 5 conductor thermostat wire.


jmscp32

join:2014-04-07
Fall River, MA

Thanks i will do that, can you tell me where do the wires go at the furnace?



mackey
Premium
join:2007-08-20
kudos:12

For the new 5 conductor cable?
Red to R
White to W
Green to G
Yellow to Y
Blue to C


jmscp32

join:2014-04-07
Fall River, MA

Thanks, do i use the same logic at the furnace?


ke4pym
Premium
join:2004-07-24
Charlotte, NC
Reviews:
·VOIPO
·ooma
·Verizon Broadban..
·Northland Cable ..
·Time Warner Cable
reply to jmscp32

Once you get this thing up and running, let us know how it works out. I'm interested in the WiFi bit.

I'm particularly interested in replacing my current Honeywell with the 9590:

»www.bestbuy.com/site/Honeywell+-···overview



mackey
Premium
join:2007-08-20
kudos:12
reply to jmscp32

said by jmscp32:

Thanks, do i use the same logic at the furnace?

Yes.