Need help with Heat Pump thermostat connection

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Need help with Heat Pump thermostat connection

Postby davisdee » Sat Jan 26, 2013 5:57 pm

I'm looking for assistance in connecting a new thermostat. I'm trying to replace a Honeywell Chronotherm IV Plus thermostat with a manual Honeywell RTH3100C, but the wiring diagram doesn't quite match. I actually have a second programable RTH6580WF in case the other doesn't work out. I have a Trane Heat Pump (two stage heat and one stage cooling). The Air Handler is a Trane, Model TWE065E13 with (Control Board 21C148502P01). The current wiring configuration is as -

Thermostat Terminal "C" ( Blue wire) Terminates on "B" control board
Thermostat Terminal "R" (Red wire ) Terminates on "R" control board
Thermostat Terminal "W2" (White wire) Terminates on "W1" control board
Thermostat Terminal "E" (Black wire) Terminates on "W2" control board
Thermostat Terminal "W1" jumped to Thermostat Terminal "Y1"
Thermostat Terminal "Y1" (Yellow wire ) Terminates on "Y" control board
Thermostat Terminal "O B" (Orange wire) Terminates on "O" control board
Thermostat Terminal "G" (Green wire) Terminates on "G" control board
Thermostat Terminal "W2" ( White wire) Terminates on "W1" control board
Un-connected wire in Thermostat ( Brown Wire) Terminates on "T" control board
Thermostat Terminal "X1" nothing connected
Thermostat Terminal "L" nothing connected
Thermostat Terminal "X2" nothing connected
Thermostat Terminal "QT" nothing connected
Thermostat Terminal "QT" nothing connected
Control Board Terminal "Y lo" nothing connected
Control Board Terminal "W3" nothing connected.

I'm also looking to replace this 20 year old system in the next few years. I'd like to put the best reliable/energy efficient system available.
Any recommendations?
davisdee
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- Need help with Heat Pump thermostat connection

Postby Freon » Mon Jan 28, 2013 3:04 pm

Thermostat Terminal "C" ( Blue wire) Terminates on "B" control board... Be sure the B terminal at the control board is the common... it usually is.

Thermostat Terminal "R" (Red wire ) Terminates on "R" control board.... Good

Thermostat Terminal "W2" (White wire) Terminates on "W1" control board..... Here you need to be careful. W1 is usually the call for heat. In your situation it would start the heat pump. That's why it's usually connected to the Y terminal at the control board. Energizing the Y also energizes the contactor at the condenser unit outside. The heat or cool control comes via the changeover valve energized by the O wire. See below for more explanation. But W2 is usually the Auxiliary heat and needs to activate the electric heat strips in the air handler when called by the thermostat... read on

Thermostat Terminal "E" (Black wire) Terminates on "W2" control board... E is for emergency heat. Usually you have the W (w1) as the primary call for heat pump heat. Then, if the house temperature is 2 degrees below the set temperature on the thermostat, the AUX heat (electric heat strips in the air handler) will be switched on by the thermostat. Once the house and set temps. are back to less that a 2 degree differential, the AUX (electric) heat will turn off. The E terminal is for Emergency heat. If, at the thermostat you call for emergency heat, it will activate the heat strips in the air handler no matter the thermostat setting or house temp. To wire the AUX (on when there's a need) and the Emergency (always on) you need to check the thermostat installation instructions. Possibly the Emergency heat is handled by W3 at the control board.

Thermostat Terminal "W1" jumped to Thermostat Terminal "Y1" ... W1 is the primary heat as I explained. Being jumped to Y1 that terminates at Y on the control board is as you'd expect... a call for 1st stage heat activates the condenser.

Thermostat Terminal "Y1" (Yellow wire ) Terminates on "Y" control board... good

Thermostat Terminal "O B" (Orange wire) Terminates on "O" control board... This is the changeover valve on the condenser. The important point here is to know whether in the heating cycle or cooling cycle the changeover valve should be energized. This is set in the thermostat setup. The condenser installation instructions should tell you or you can set it one way at the thermostat and see if you get the expected heating or cooling.

Thermostat Terminal "G" (Green wire) Terminates on "G" control board... Good, this is the main blower (fan) control line.

Thermostat Terminal "W2" ( White wire) Terminates on "W1" control board. Here is where you need to read what W2 is for that thermostat. I suspect it is the AUX and possibly should be on the W2 which I assume activates the heat strips in the air handler.

* wire in Thermostat ( Brown Wire) Terminates on "T" control board.... I would ignore this. The T wire is usually made for Trane only thermostats

The rest below seem correct. The only question is where on the control board would the Emergency heat connection be. See if you can find a schematic of the air handler. It's usually inside on the door of the main blower compartment.

Thermostat Terminal "X1" nothing connected
Thermostat Terminal "L" nothing connected
Thermostat Terminal "X2" nothing connected
Thermostat Terminal "QT" nothing connected
Thermostat Terminal "QT" nothing connected
Control Board Terminal "Y lo" nothing connected

Control Board Terminal "W3" nothing connected... This MAY be the Emergency heat connection. It is not necessary unless you want it.
Freon
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