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Have a 4 wire ac/heat system, installed new thermostat, cannot reconnect them as the leads were not labeled and the old thermostat was broken

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  • dwkcool May 11, 2010

    what color are the 4 wires and what king of ac/heat is it

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Give me the the model number and Mfg of your equipment along with the color codes at the unit, not the thermostat wire at the thermostat, and I can assit. Contact me directly.

Richard (Rick) Drennan
Global HVAC Distributors
Field Support Representative / Instructor
rdrennan@globalhvac.com
900 Spreckels Ave
Manteca, Ca. 95336
Office (877)448-7263
Cell (209)456-0513

Posted on Jan 05, 2009

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All is standard, heater is gas, AC is electric, old thermostat was old and burned. I have TH3110D1008 and 4 wires.


the colors on standard t-stat are rh/rc gets red wire. g goes to fan green. y goes to outside unit cool. and in your case w labeled black goes to heat normally this wire is white.

Jul 25, 2015 | Air Conditioners

Tip

How to change a thermostat yourself


Choosing your new thermostat:
Firstly you have to ask yourself why you are changing your thermostat. Is your old thermostat simply broken? Are you wanting a simple upgrade from analog to digital? Are you looking to save on energy costs using a programmable? Are you attempting to integrate your central system into a smart home network? Whatever the reason your choice of thermostat should not be simply the cheapest on the shelf. Different system types may require different thermostat types.
Before purchasing your new thermostat you need to figure out what kind of system you have. The general idea is *H/*C, denoting the number of heating/cooling stages and options, and fuel type (heat pump, gas furnace, electric furnace, etc.). An example would be a typical heat pump- it has a single cooling stage and a dual heating stage (heat strips, compressor) making it a 2H/1C heat pump thermostat. I usually install the Honeywell FocusPro 5000/6000 series for non-programmable/programmable applications for it's ease of use and general reliability.

Before beginning the swap always make sure power is off to both the indoor and outdoor sections!

Determining which wires go where:
First off, you may not ever rely on wire colors to guide you to the proper terminal. We have standard practices for wire color to function, but this varies from region to region and sometimes if a wire shorts out a substitute in the bundle may be used. When removing the old thermostat physically writing down or labeling the wires is not an exercise in tedium- it is almost necessary and something which I do every single time. You will usually have these terminals on the new device:
Rc- Cooling Power (usually jumpered to R/Rh)
R/Rh- Heating Power (usually jumpered to Rc)
Y- Primary Compressor
C- Common
O/B- Reversing valve (activated in cooling/heating)(Heat pump)
W- Primary heat (Furnace or Electric heat)
G- Indoor Blower
E/Aux/W2/X2- Emergency/Secondary heat stage
Y2- Secondary Compressor (2 stage cooling)
L- Communicator for E-Heat (Heat pump)
If you do not have all of the terminals on the old as you have on the new it may not be the end of the world. Required terminals are an R, a Y (if AC is present), a W/W2/E/Aux/X2 (if heat is present), an O/B (if heat pump), and usually a G. Common is optional most of the time as it is used to power the thermostat only and batteries may be substituted. L is not commonly used. If you have any doubts as to which wires go where, stop now. Miswiring can destroy a system's low-voltage and potentially start a fire.

Replacement:
After labeling the old wires and removing the old thermostat, you must attach the new baseplate. Leveling the baseplate is not as important as it was with older mercury thermostats, but still applicable at least within +-5 degrees of rotation. If you are attaching the baseplate to drywall with no backing wood installing wall anchors (usually supplied) is key. Make sure you have a proper length of bare wire (not too long, not too short) before attaching to the terminals. Do not overtorque the screw lugs. Pull back on the wires after attaching them to ensure the connection is proper. It is a good idea to plug the hole through which the wires come with something (I use plumbers putty) to keep a draft from effecting the thermostats temperature. Many thermostats will require some pre-programming before hooking up (refer to installers guide)- I find this much easier to do via batteries before attaching the face to the baseplate. Once the face is on and the power returned to equipment, test the system. Keep in mind modern thermostats include a 3-5 minute delay for compressors as a protective layer.

Common Pitfalls:
Zone system wiring can be confusing and is not as standardized as it should be. If you have a zone system and plan to purchase new thermostats it is highly recommended to call in an experienced service technician.
High SEER and IQ drive systems use very different types of thermostats than conventional systems. For now the newer technology has yet to be perfected in the public market and these changeouts are best left to an experienced professional.
Some older thermostats use B as common (Trane Weathertron for example) This is not to be confused with B as a heating changeover valve and if it is can blow out a fuse,transformer, and/or your brand new thermostat upon startup.
Most face to baseplate interfaces are pin based- if one is not quite careful bending one of these pins during attachment can be irreparable.
Common is the least standard color across installers. Most use either brown or blue, but I've seen some use green and black, usually used for blower and secondary heat respectively. Never assume wire color as a standard.
Most of the service calls regarding thermostats I receive come from homeowners who have purchased and self installed incompatible thermostats. This is something I do everyday for a living, not so for the average homeowner. Take your time and do your research.
Save your manuals- all of them. Many cheap offbrands can be next to impossible to find manuals for online.
When in doubt, call in a pro. Most of us charge around $70-100 to install a thermostat (plus cost). This is almost always much cheaper than a service call to diagnose and repair a low voltage problem.

on Sep 25, 2011 | Air Conditioners

1 Answer

How to hookup Auxiliary heat (and/or use an extra wire at the thermostat)


They don't always use the correct wire colors,if it is labeled w it is for your strip heat,shouldn't hurt to hook it up,most likely they used it for the strip heat,most heat pumps are wired to turn on your strip heat when the heatpump is in defrost mode and it is controlled by the heat pump,you can hook this to the emerg. heat or w2 :)

Mar 08, 2013 | Ruud Air Conditioners

1 Answer

Carrier OEM to Honeywell Programmable Tstat - NEED HELP


you likely have a "two stage" system, but not a two stage heat pump. the first stage is probably the heat pump itself, and the second stage is the auxilliary resistance heat that suppliments the heat pump at lower temps. if i knew the terminals that are available on the new stat, i could advise you on the proper wiring.

Jan 27, 2013 | Carrier Air Conditioners

1 Answer

Havc thermostats


I will assume you did not write down what color wire you took of each letter on old thermostat? Sometimes color of wire doesn't matter as some installers will use whatever color. If you noted where each wire was on old thermostat, just put same color wire to same letter on new one. Under normal situation. y is for compressor (cool) G, is for fan (on AC) , RC is 24 volts from transformer for AC side, RH is 24 volt transformer from heat/furnace, and W is for other wire from furnace, is furnace is only 2 wire system. Was there any wire connected to A on old thermostat?

Apr 11, 2012 | Air Conditioners

3 Answers

Installed a new Filtrete thermostat on a new Carrier high-efficiency furnace. I followed instructions exactly. It doesn't work. What did I do wrong? Furnace was installed in December. Broom handle...


Hi smargyle,

Welcome to fixya!

I can provide you with diagrams for the old Carrier therm and for the new Filtrete therm. But, I would need to know what the model numbers are for each therm plus how many speeds AC you have.

Please reply back with that information and we will get your AC back in working order.

Thanks,

Handie Andie

Jul 22, 2011 | Air Conditioners

1 Answer

I have a Trane XE1000 High Effeciency heat pump, installed in 1989, in the house I am renting. I'm having issues with the air and I think I hooked the thermostat up wrong. I have 8 wires coming out of...


The white wire goes to W2, the green wire goes to G, the red wire goes to R, the orange wire goes to W or O, and the Yellow goes to y. If this is a digital thermostat you will have to go to the set up mode to set the system up for a heat pump or the reversing valve in the outdoor unit will be in the heat mode. If there is a C on the thermostat you will need to put the black wire there on some Trane models.

Jun 06, 2011 | Air Conditioners

1 Answer

AC unit not kicking on...


You need a "Y" terminal. "Y" is pretty standard on every heat pump. It is the wire that will energize the compressor contactor at the outdoor unit, allowing the compressor and condensor fan to run.

Apr 03, 2010 | Air Conditioners

1 Answer

Newly installed Goodman GPG13 gas/electric package unit installed. Cannot get AC to cycle on. Unit produces heat at all thermostst settings.


new unit and old thermostat/wire? thermostat could be bad or bad thermostat wires. try putting in new of anything old. do this wiring practice with the terminals being the letters.

r- red (24 volts)
w- white ( heat)
y- yellow (cooling)
g- green (fan)

Sep 21, 2008 | Goodman Air Conditioners

1 Answer

I tried to replace my digital manual Honeywell thermostat that is only 6 months old (new construction) with a programable thermostat. I followed the instructions marking the wires and connecting them up...


Your "R" terminal is basically your "hot" and your "C" terminal is basically your "neutral" to simplify explanation. The Furnace supplies the "R" power to the thermostat and then depending on what wire the thermostat sends the power back on determines what the system does. The thermostat terminals are as follows "G" is fan, "W" or "aux" is elect heat, "Y" tells the outdoor unit to run, "O" or "B" tells the outdoor unit whether it is heating or cooling, and "E" is emergency heat. "G" should connect from the t-stat directly to the furnace and go no further. "W" or "aux" AND "E" should both connect to your "W" or "W1" terminal in the furnace, there should also be a "W" connection to the heat pump ( this allows the H/P to turn on the elect heat when the unit defrosts) "Y" and "O" or "B" may or may not connect to a terminal in the furnace, usually they just pass through the furnace from the t-stat to the H/P and get wire nutted in the furnace. Now, here is the key. As I mentioned previously "O" or "B", a system will only use one or the other. The entire industry (except for Rheem and Ruud) uses the "O" terminial which has 24v on it when you are cooling and no power when you are heating. Rheem and Ruud use the "B" terminal which is just backwards, 24v in heating and no power in cooling. This is all for a heat pump, If you do not have a heat pump, then disregard the references to "O", "B", "E", and "aux". You will have R-power on red wire, W-heat signal to furnace, G-fan signal to furnace, and "Y" cool signal to outdoor unit.

Jun 08, 2008 | Honeywell Air Conditioners

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