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mercury416

join:2005-11-13
Gainesville, FL

goodman GMP050-3 Gas Furnace where to find 24vac

Trying to upgrade the thermostat for my Goodman GMP050-3 gas furnace serial number 0104627616 with a Honeywell RTH6580WF Wi-Fi 7 Day Programmable Thermostat. The instructions on the thermostat state that it requires a 24vac common wire. My current thermostat does not require a 24 VAC common wire, I have already verified that there are spare conductors on the wire from the old thermostat to the furnace. My question is in the hookup of the new thermostat . I looked at the manual for the furnace and the terminal screw labeled "HUM"is designed to provide a 24vac signal in heater mode (page 24 of the manual) is this the correct place to get the 24 VAC or do i need to install a separate transformer to obtain the 24VAC or is there another location to get the 24 VAC signal . My fear is that the 24VAC from the "HUM" terminal will not be provided in both the heating and air conditioning modes. My assumption is that the thermostat requires 24VAC at all times .Is there a better way to do this ?

thanks for your assistance

any questions in case i have not provided enough information please ask


Tex
Premium
join:2012-10-20
kudos:2
Look on the control board for a "C" terminal. There should be R, W, G, Y on the board. "C" is usually the last one. That's your common.

mercury416

join:2005-11-13
Gainesville, FL
control board only has terminals W,G and R


Tex
Premium
join:2012-10-20
kudos:2
Do you have A/C? If so, look for the low voltage cable going to the condensing unit. The "Y" wire from the thermostat (yellow or blue) goes to one of the wires going outside. The other wire is common. Or, you could look on the wiring diagram to see which low voltage wire coming off the transformer is common. It's the one NOT feeding "R".

mercury416

join:2005-11-13
Gainesville, FL
yes have a/c ( I live in florida) let me look be right back

mercury416

join:2005-11-13
Gainesville, FL
reply to Tex
going to the condenser unit there are two wires connected. yellow and blue. The blue is a three way splice, the yellow goes from the position labeled cooling stage one on the old thermosat to the the condensing unit


tp0d
yabbazooie
Premium
join:2001-02-13
Carnegie, PA
kudos:6

1 edit
blue is your common wire. tap in at the splice, or make your own if its a crimp on

if you have a multimeter, check for 24v from the blue to white (W)

-j
--
if it aint broke, tweak it!!
currently on FiOS (kick aZZ!)

mercury416

join:2005-11-13
Gainesville, FL
should i see 24 VAC on this wire


leibold
Premium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:10
Reviews:
·SONIC.NET
said by mercury416:

should i see 24 VAC on this wire

Depends between which two terminals you measure.

Between Blue (the terminal should be labeled C) and R (typically a red wire) you should have 24V AC regardless whether the thermostat is calling for heat, cooling or nothing at all.

Blue is one of the colors frequently used for the C terminal (common wire). Unfortunately the color varies sometimes.
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mercury416

join:2005-11-13
Gainesville, FL
reply to tp0d
after further examination when the system was installed one of the legs of the three way splice of the blue wire was the wire going to the thermostat so it seems like all i have to do is put the new thermostat in place and use the blue wire on the thermostat wire as my common . It seems that since the original thermostat did not require a common it simply was not hooked up but the connection was made in the furnace. Knock on wood tomorrow i will get this new thermostat installed . Thank you all for leading me to find the blue wire as my common it was not readily apparent


tp0d
yabbazooie
Premium
join:2001-02-13
Carnegie, PA
kudos:6
np.. pass it along.

-j

mercury416

join:2005-11-13
Gainesville, FL
just a quick update today i installed the new thermostat, connected to the wireless network at the house and off to the races . Once again thanks to all who contributed