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dflorcik · Dec 23, 2008, 05:11 PM

I have a Coleman furnace and air-conditioner unit and I want to replace the thermostat. The old one has wires connected to the 'Y', 'G', 'W', 'R' and 'A'. I can't find where to connect the wire that was connected to the 'A' terminal on the old thermostat to the new thermostat. Would anyone know?

Thanks,
Dave

MarkwithaK · Dec 23, 2008, 06:52 PM

Are we to hope that Santa brings us the gift of specific information (i.e. make, model) of your stat and furnace?

KC13 · Dec 23, 2008, 11:13 PM

Check the thermostat wire connections at the furnace. Find the wire that was connected to the "A" thermostat terminal. What letter designates the terminal that this wire is connected to?

hvac1000 · Dec 23, 2008, 11:21 PM

Santa may not come this year since he was ripped off in the hedge fund market.

KC13 · Dec 23, 2008, 11:23 PM

I heard he got an insider tip, cashed in, and boarded a plane. Or was that bought a plane?

dflorcik · Dec 24, 2008, 03:50 PM

It is a Coleman Furnace model 3115-750 with an Intertherm split system air-conditioner. The thermostat is an Intertherm. There are two numbers on the thermostat: 65A-84-634 and 8045. There two multi-conductor wires going to the thermostat. The first has three wires in it and they are connected to the G, R, and Y terminals. The second has two conductors and they are connected to the W and A terminals. The second two conductor wire seems to go to the high voltage section of the unit behind the fuses above the heating elements. I can't see beyond that.

ballengerb1 · Dec 24, 2008, 04:43 PM

Ok not from Santa but this old post should be helpful to you. https://www.askmehelpdesk.com/heatin...eat-58313.html

dflorcik · Jan 5, 2009, 03:12 PM

Actually it wasn't helpful.

hvac1000 · Jan 5, 2009, 03:38 PM

There are no A terminals listed on my master chart of thermostat connections. It is possible this thermostat was made special especially if this is in a mobile home or modular home. The older mobile home units were add on units and they had some crazy wire configurations. Sorry

ballengerb1 · Jan 5, 2009, 07:11 PM

This is a quote from Northern heat "Thermostat wire color codes explained.
Please note. Not all installers use the proper color codes when they install or replace equipment. It may be necessary go go to the furnace or outdoor unit to verify what wires are for what purpose. Also be sure there are no splices in the wire that could change the wire colors between components.

R (red) or Rh (Red heat) 24 volts from equipment.
Rc (Red cooling) 24 volts from transformer in cooling equipment.
Note: If only furnace has a transformer and cooling equipment does not jumper Rc and Rh.
W (White) sends 24 volts to furnace control to start the heating cycle.
W2 (no standardized wire color, usually whatever wire color is available) controls second stage heat.
Note: W2 is most often used for heat pumps to control what is called emegency heat or Auxillary heat, and most often will use the white wire.
Y (yellow) often (blue) is used, controls cooling unit (outdoor condensing unit) also is used for heat pump heat.
Y2 (no standardized wire color, usually whatever wire color is available) controls second stage cooling.
G (Green) controls the fan "on" operation of the furnace/air handler. Also often is used to start the blower for many electric furnaces.
C (common) most often brown but can also be black or other color available to installer.
O (orange) Energizes heat pump reversing valve for cooling (Trane and most other brands).
B (Blue) Energizes heat pump reversing valve for heating (Rheem, Ruud and Weatherking). "
Based on this info I agree with HVAC , we don't normally see a terminal A. Any chance of a picture?

KC13 · Jan 5, 2009, 07:16 PM

Originally Posted by KC13

Check the thermostat wire connections at the furnace. Find the wire that was connected to the "A" thermostat terminal. What letter designates the terminal that this wire is connected to?

It looks like you will have to pursue this, like it or not. It's what I would do when in doubt on a service call.

dflorcik · Jan 14, 2009, 04:14 PM

It is in fact a mobile home built in 1985. I think that I'll have to draw up a schematic of the thermostat.

acetc · Jan 14, 2009, 07:02 PM

From your explanation it makes me think that you have a two transformer system, the a/c system using the r, y, g terminals and the w and a terminals for the heating. If this is the case you will need a thermostat with an RC and a RH terminal as well as the Y,G,W terminals. You would connect the wire from the A terminal on the old thermostat to the RH on the new thermostat , the R would connect to RC, the G to G, the W to W, make sure there is NO jumper between RC and RH. Good luck, Mike

hvac1000 · Jan 14, 2009, 07:13 PM

It is in fact a mobile home built in 1985

Back in 1985 Coleman and other manufactures had a cool off heat switch right on the furnace so your system was probably field installed and did not come from the factory wired that way especially since A/C was always a add on back then. I have all the old Coleman/Miller books and none of them show a connection.