Author Topic: Thermostat wiring question (Read 4801 times)

redrocker

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Thermostat wiring question
« on: December 15, 2015, 08:41:39 AM »
I need to replace my old thermostat, as the buttons aren't very responsive anymore.

I've changed a few and they've always been straightforward but this one has some different wiring going on. Attaching a picture below. The existing thermostat is a Totaline (model# P474-0100 if it matters). I'm trying to install a Honeywell RTHL3550D from Lowe's.

Existing thermostat has 6 wires, connected as follows:
Red wire connected to "R"
Green wire connected to "G"
Yellow wire connected to "Y1"
White wire connected to "W2"
Brown wire connected to "B/O/W1"
Light blue wire connected to "C"

I'm pretty sure the tape labels on the wires were put on there by me a year ago when I first opened it to replace it and subsequently gave up when I couldn't get the A/C to turn on and just reinstalled the old thermostat. So I'd ignore the tape labels on the wires.

I'm pretty confident that I do not have a heat pump. My home inspection report states that the HVAC is "forced air unit with gas heat." However, when I googled "thermostat brown wire" it seems that it is commonly for a heat pump, especially when there's a separate wire that goes to the "C" connection.

The Honeywell instructions for the new thermostat state that for conventional wiring I should not connect the C or the B wire (or X if I had it) and should wrap those wires in tape.

Just curious if anyone has any experience with an older thermostat with such a wiring setup and how I should proceed with a newer thermostat. Thanks

DaveR

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Re: Thermostat wiring question
« Reply #1 on: December 15, 2015, 09:14:57 AM »
The only way to know for sure what's what is to look on the furnace itself and trace the wires. However, things are generally standard. Your brown wire is likely equivalent to orange, so for the Honeywell, it should be:

Red wire connected to R-Rc (jumpered) [power]
Green wire connected to G [fan]
Yellow wire connected to Y [cooling]
White wire connected to AUX [heat]
Brown wire connected to O/B [reversing valve]
Light blue wire not connected [common, Honeywell battery powered, so not needed]

This is per the diagram on Page 24 of the manual (heat pump wiring).

redrocker

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Re: Thermostat wiring question
« Reply #2 on: December 15, 2015, 12:33:19 PM »
The only way to know for sure what's what is to look on the furnace itself and trace the wires. However, things are generally standard. Your brown wire is likely equivalent to orange, so for the Honeywell, it should be:

Red wire connected to R-Rc (jumpered) [power]
Green wire connected to G [fan]
Yellow wire connected to Y [cooling]
White wire connected to AUX [heat]
Brown wire connected to O/B [reversing valve]
Light blue wire not connected [common, Honeywell battery powered, so not needed]

This is per the diagram on Page 24 of the manual (heat pump wiring).

Tried this alignment. The heat worked, and the fan came on as well, but the A/C didn't respond when I went to "cool."

Pulled the B wire out and left it disconnected. Now the A/C does come on when I go to "cool" but the heat doesn't come on now. (Help?)

redrocker

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Re: Thermostat wiring question
« Reply #3 on: December 15, 2015, 12:50:11 PM »
Just tried moving the white wire (previously in "W2" or "Aux") over to "W1".

So now I have:
Red wire connected to "R"
Green wire connected to "G"
Yellow wire connected to "Y"
White wire connected to "W"
Brown wire disconnected
Light blue wire disconnected

Again, the A/C works, but the heat is not coming on still.

guitar_stitch

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Re: Thermostat wiring question
« Reply #4 on: December 15, 2015, 01:14:51 PM »
Many T-stats jumper W1 and W2.

Based on your description, I would say that you do have a heat pump. That's what the reversing valve is for.

Be sure that when you plug in the thermostat, you give it at least 10 minutes before deeming it "not working". Many thermostats have a built in delay timer that prevents the compressor from coming on after a power failure while the head pressure is still high and damaging the compressor.

DaveR

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Re: Thermostat wiring question
« Reply #5 on: December 15, 2015, 01:23:09 PM »
I found the P474-0100 manual: http://ntsupply.com/files/products/p4740100install.pdf

pg. 4 has the wiring. Based on the photos, your current wiring matches up with what I said earlier for the Honeywell...

redrocker

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Re: Thermostat wiring question
« Reply #6 on: December 15, 2015, 01:55:14 PM »
I found the P474-0100 manual: http://ntsupply.com/files/products/p4740100install.pdf

pg. 4 has the wiring. Based on the photos, your current wiring matches up with what I said earlier for the Honeywell...


This may be obvious to someone more experienced but perhaps your first post is correct and I just don't have the settings dialed in right. Page 13 of the Honeywell manual is what I'm trying to decide on. I tried Function 1 set at 1 - Heat Pump. When I attempted to turn the heat on, the A/C unit kicked on outside. So I scratched that setting.

Then tried Function 1 set at 7. Currently testing.

mankyle

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Re: Thermostat wiring question
« Reply #7 on: December 15, 2015, 02:34:32 PM »
" I tried Function 1 set at 1 - Heat Pump. When I attempted to turn the heat on, the A/C unit kicked on outside. So I scratched that setting"

However, if you actually have a heat pump (with auxillary gas back-up) then the outside A/C unit will run when the thermo is set to the "heat" setting. Did you let it run long enough to see if it actually pushed hot air through the ducts?

I would go back and try that setting and see if you are getting cold or hot air.

As for the home inspection report, that could be wrong. I would check the outside unit for a model number and search that to see if it is an A/C only or a heat pump unit. You might also be able to find info on the thermo connections, ditto with the furnace.

redrocker

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Re: Thermostat wiring question
« Reply #8 on: December 15, 2015, 02:38:11 PM »
Feels like both heat and a/c are working now. Returned to the originaly proposed wiring, thanks to DaveR:

Red wire connected to R-Rc (jumpered) [power]
Green wire connected to G [fan]
Yellow wire connected to Y [cooling]
White wire connected to AUX [heat]
Brown wire connected to O/B [reversing valve]
Light blue wire not connected [common, Honeywell battery powered, so not needed]

The initial problems I had getting the A/C to kick on were apparently due to not having the functions setup properly within the thermostat. So last question, I have it wired as a heat pump system, with the function selected for multi-stage heat. Honestly, not sure what is meant by multi-stage heat and was previously under the impression I did not have a heat pump.

With both heat and cooling working now, should I be at all concerned about doing damage to the system since I pretty much set up the function by trial and error (ie, what if I'm supposed to be a different function to operate optimally)?

mankyle

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Re: Thermostat wiring question
« Reply #9 on: December 15, 2015, 02:57:33 PM »
So, with your current setup does you outside A/C unit still run when you switch to heat? If so, then you definitely have a heat pump.

As I understand it, multi-stage heat simply means that at moderately cold temperatures, the heat pump will function to provide the heat to your house. If the outside temp gets too low then the "auxiliary heat" kicks on (which in your case sounds like a gas furnace). I live in NC and most of the heat pumps here have an electric backup which can get expensive if temps drop for an extended period of time. However, I looked up what you likely have and the call it a "dual fuel heat pump" and it sounds like a more economical way of doing things.

http://homeguides.sfgate.com/dualfuel-heat-pump-gas-furnaces-work-89030.html

http://familyhandyman.com/smart-homeowner/energy-saving-tips/efficient-heating-duel-fuel-heat-pump/view-all

Again, I would gather the model numbers for the furnace and outside unit and do some sleuthing to be sure that is what you have. If you can't find it on the web, call a heating/cooling supply store with the info, they will likely be able to help out.


Gibbelstein

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Re: Thermostat wiring question
« Reply #10 on: December 15, 2015, 03:55:37 PM »
RR,
For what it is worth, the way that has always worked for me is to match the wires up to the letter on its terminal on the old thermostat. (For instance, if the wire on the "W" terminal in the old thermostat was brown, it goes to "W" not "Br", or whatever). Also, my limited experience with HPs agrees with mankyle's description of what a multi stage heat pump. Some climates don't ever get cold enough to need the backup and can just get away with the HP, which is why the distinction exists. But, I seem to recall that there is a way to "force" the thermostat to activate the second heating source. That would allow you to manually check the furnace to make sure that it is wired correctly and will come on when the thermostat says it should be on.

Other settings are often all in the thermostat. For instance, the reversing valve in my HP is "backwards" from the standard, so I had to choose an option in the thermostat to reverse that (otherwise it would heat on AC and cool on Heat). There is sometimes an option specifically for "Heat pump with AUX heat".

Good luck,
Chris

redrocker

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Re: Thermostat wiring question
« Reply #11 on: December 15, 2015, 04:11:05 PM »
So, with your current setup does you outside A/C unit still run when you switch to heat? If so, then you definitely have a heat pump.

My previous setup with the old thermostat, the outside unit never came on. Only today when trying to figure out the wiring for the new thermostat. The A/C came on when I turned on the heat *only when* I had the wiring as DaveR proposed and had changed Function 1 to 1. My current setup at the moment is with the wiring still as proposed, with Function 1 set to 7 (Two heat stages, one cooling stage). With that setup, the outside unit stays off, but the heat comes on, similarly to how it did with the old thermostat. So I think I'm close.


Again, I would gather the model numbers for the furnace and outside unit and do some sleuthing to be sure that is what you have. If you can't find it on the web, call a heating/cooling supply store with the info, they will likely be able to help out.


Outside unit is labeled as an air conditioner (pic attached below). I can't access the furnace at the moment (in the attic, access through a tenant's closet) but I'll check that when I can to confirm what I have.
Thanks for the info on multi-stage heat!

wienerdog

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Re: Thermostat wiring question
« Reply #12 on: December 15, 2015, 09:28:11 PM »
Do you have a volt meter? If you do put the setting on AC voltage and measure between the C wire (light blue) and the red wire. You should measure 24 VAC.

If that is the case touch the red wire to the green. Your blower on the air handler/furnace should turn on.

Now touch the red wire to the yellow wire. The outdoor unit should come on. Note if you leave it on a long time you should also connect the red to the green at the same time as the yellow. (If you do turn the outside unit on let it sit for 5 minutes before you try to turn it on again)

Now touch the red wire to the brown wire. The furnace should turn on. I would also touch the green wire at the same time and leave it there to see if you get heat from the vents.

Give us some feedback on what those three things do.


guitar_stitch

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Re: Thermostat wiring question
« Reply #13 on: December 16, 2015, 10:22:24 AM »
http://s3.amazonaws.com/bobspdf/mn/j/L0522717.pdf

Check the outdoor wiring. If you have the "O" terminal connected inside the condenser unit, you have a heat pump.

mankyle

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Re: Thermostat wiring question
« Reply #14 on: December 16, 2015, 10:57:38 AM »
I found the same manuals at Sears Parts Direct. They were under the A/C-heat pump heading but that may just be a catch-all category, not a definite answer on what you have.
http://searspartsdirect.com/partsdirect/part-model/Icp-Parts/Air-Conditioner-Heat-Pump-Parts/user-manuals/manual-downloads/Model-TCA460AKA1/0492/0904000?modelNumber=TCA460AKA1&diagramPageId=&documentId=

If you have the heat pump connections as described then this should allow you to figure out how to hook it up. If you don't, then it sounds like you have it figured out. It could be that the outside unit used to be a heat pump but had been replaced with an A/C only and the wires never removed from the thermostat. By looking at the outdoor unit you should be able to figure out what is what.

Also, I found the ICP website but they have little accessible info and the website isn't searchable. You might be able to use the feedback form to get a hold of them or try and find a phone number.
http://icpusa.com/who.html#

Good luck with it and definitely let us know what you find out.



Sibley

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Re: Thermostat wiring question
« Reply #15 on: December 16, 2015, 11:04:05 AM »
I found calling their help line very helpful. I told them what I saw, and they told me what to do.

Agg97

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Re: Thermostat wiring question
« Reply #16 on: December 16, 2015, 02:06:33 PM »
I would open up the panel on the furnace/blower/air handler (whatever you want to call it), and look where the brown wire is connected.

It should be relatively simple to tell if you have a heat pump: if you have a flue, it's a gas furnace. If there's no flue, it's a heat pump or you simply have electric resistance heaters. If your outside condensing unit comes on during heat mode, you have a heat pump. If it does not, and there's no flue, you have electric resistance heaters.

One thing to note is if you DO have a heat pump, be sure to get a thermostat that is specifically made for a heat pump. A standard thermostat will run the "emergency electric resistance heater" on a heat pump too often and you'll be losing a lot of the energy savings with having a heat pump.

Can you see a make and model # on your indoor unit as well? That might help.

Agg97