Thermostat Wiring for heat pump)

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Old 08-07-15, 04:47 PM
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Thermostat Wiring for heat pump)

Hello All,

I would appreciate your help in figuring out how to install a new heat pump t-stat. I'm just not up to racking my brain over it and need some input soon due to no air at the moment.

The existing t-stat is a Total Line P374-0300 as found (HERE). It's a very inexpensive and basic t-stat. My unit is a two stage heat pump with auxiliary 10kw heat strip, btw.


*The existing t-stat hookup is as follows: See image below...

"W" = white wire
"O" = green wire (#2). This is an apparent extra wire they used, so color
maters not.
"G" = green wire (#1)
"R" = red wire
"C" = blue wire
"Y" = yellow wire


*My new thermostat has 8 terminals as follows: It is a Honeywell RTHL2410C purchased at Lowes.

"B"
"O"
"G"
"Y"
"W/Aux"
"not used"
"R"
"Rc"

There is a jumper between "R" and "Rc".



Anyhow, my feeble mind tells me the existing red wire will go to "R/Rc", yellow wire will go to "Y", green wire(#1) will go to "G", white wire will go to "W/aux" for heat strip.

That leaves the extra green wire(#2) and the blue wire left over. They apparently are used for "RVS Cooling" and "24 VAC Comm" as depicted in the image below? So where do those attach to the new t-stat?
 
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Old 08-07-15, 05:25 PM
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The C wire (blue) is your common wire which is required for thermostats which DON'T run on batteries. I believe the 2410 does run on batteries so you don't need it. Tape it off.

The second green wire "O" is your reversing valve. That should connect to "O" on the new stat.
 
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Old 08-07-15, 08:37 PM
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Thanks Bob,
I just read that particular t-stat isn't compatible with multi-stage units. However, I purchased two just in case and the second (Honeywell RTHL3550D) apparently is compatible because it doesn't denote incompatibility as the other does.

The other wiring diagram is straight forward as such....See image below.


Red wire = R/Rc
Yellow wire = Y
Green wire(#2) = O/B
Green wire(#1) = G
white wire = Aux/E

Tape off blue wire as this t-stat has batteries....

God Bless,
Ralph
 
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Old 08-08-15, 05:24 AM
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Good you got it worked out, but I'm a little confused. Maybe I am mistaken but your system does not look like it is a multi stage system. A multi stage system usually has a Y and Y2.

Maybe you're thinking that a heat pump with back up heat is what is being refereed to as 'multi stage'?

At any rate, unless I'm mistaken and there is a Y2 hiding there somewhere, the other Honeywell would have worked fine and you have a SINGLE stage heat pump with back up/emergency heat. Moot issue though if you got it working.
 
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Old 08-08-15, 09:55 AM
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You will need to place a jumper wire between Aux and E on the new thermostat since it is two separate terminals.

A heat pump with Aux heat requires a multistage thermostat.
 
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Old 08-08-15, 12:59 PM
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A heat pump with Aux heat requires a multistage thermostat
I think there is a bit of confusion on exactly what "multi stage" means.

The 2410 install manual clearly states that the stat works for heat pumps with backup/AUX heat. It also CLEARLY states it can not be used on multi stage systems. In other words a stat which controls a heat pump as well as AUX heat is not considered a multi stage stat.

Identify System Type

This thermostat is compatible with the following systems:

Gas, oil or electric furnace
Central air conditioner
Hot water system with or without pump Millivolt system
Central heating and cooling system
Heat pump without auxiliary/backup heat
Heat pump with auxiliary/backup heat

Do you need assistance? We are here to help.

Call 1-800-468-1502 for wiring assistance before returning the thermostat to the store.

This thermostat cannot be used on multistage systems.
 
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Old 08-08-15, 01:44 PM
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That is strange because the heat strips are stage two heat.

If you have more than one stage of heat it is multiple stages of heat.

I wonder when Honeywell changed the definition of multistage.

The old Honeywell T87 round thermostats would support single stage heat pumps.

I saw in the combination 24 and 25 manual that it supports heat pumps with Aux heat but wasn't sure if that was only the 2510.
 
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Old 08-08-15, 02:50 PM
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Well I think that back up heat is now pretty much a standard with heat pump installs, and they key term there is "back up".

A "stage" is used during normal operations to amplify heat/cool output, while "back up" is only used in case of primary failure of some fashion and it not used during regular operations.
 
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Old 08-08-15, 03:32 PM
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It sound like the difference between Aux heat and emergency heat.
 
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