Hi,

Thank you for your help in advance.
Just bought a Honeywell programmable thermostat RTH7400 to replace an older Honeywell mercury thermostat (I think its model is Honeywell Heat Pump thermostat 8919)

My old one had:

G, Y, R, O, W2, X, E

The manual's Alternate wiring scheme (for heat pumps only) has instructions for

G=G
Y=Y
R=R
O=O

It says connect W2 to AUX and E to E, but then I am left with X which is supposed to be E as well.

Does that mean that I need to connect two wires E and X to the same E on the new thermostat?
This is a second model I am trying (the previous one I bought was not matching at all).
Called Honeywell tech support and naturally after navigating for half an hour though their options discovered that they want me to call during the normal business hours :(

Any help will be greatly appreciated.

Alex

First here is your manual on line.

http://customer.honeywell.com/techli...0s/69-1726.pdf

Follow the instructions especially the one about not using the color code on the original thermostat to wire your new thermostat.

Next trace the wires from where they are located on your furnace/air handler and place them in the appropriate location on the new thermostat.

You can also look on the first page of this section and look at the sticky notes in regards to thermostat wiring. This is how a real service tech would do your install. This way you take no chances with damaging your new thermostat.

Thank you!
I'll try this manual although it looks like it's the same scheme I already tried.

I am only afraid I won't be able to trace the wires.

I live in a condo on the third floor - 1920 brick building with my heat pump on the roof :(
When they converted to central air they'd hidden all the wires behind the wall so I can't quite figure out how to trace them. I went up to the roof and took pictures of what I could trace as well as the old thermostat.

If the wire I took a picture of on the roof (going into the heat pump) is the same as the wire sticking out of my wall the difference is in the back wires

My old thermostat is connected to

White W2
Blue X
Red R
Yellow Y
Green G
Orange O
Black or some real dark color E

Up on the roof going to heat pump as the picture shows there are

White
Blue
Red
Yellow
Orange

Black and Green with some other wires are not connected. Those other wires make me think it's may not be the same wire. I don't know this is really confusing.

Older systems and base signals on newer ones
Terminal Probable
wire Color Signal Description
C Black 24 Vac Common From one side of the 24Vac transformer (Think of this as 24Vac neutral
R or V Red 24 Vac Power to be switched From other side of the 24Vac transformer (Think of this as 24Vac L1)
Rh or 4 Red 24 Vac Heat call switch power Same as R, but dedicated to the Heat call switch
Rc Red 24 Vac Cooling call switch power Same as R, but dedicated to the cooling call switch
G Green Fan Fan switch on thermostat - is connected to R when Fan /Auto switch is in the fan position
W White Heating call Is connected to R or Rh when themostat calls for heat. (Might be jumpered to Y on a heat pump. On others might be second stage heating
Y Yellow Cooling call Is connected to R or Rc when themostat calls for cooling. Also Cooling or 1st stage heating on a heat pump
Most often connected to G when Fan switch is set to auto
New signals - for heat pumps and staged systems
Terminal Probable
wire Color Signal Description
Y2 Blue or Orange 2nd stage Cooling
W2 Varies Second Stage Heating First stage Auxiliary heating on a heat Pump
E Varies,
blue, pink,
gray, tan Emergency heat relay on a heat pump. Active all the time when selected, usually not used. Disable the heat pump and turn on first stage Aux heating
O Varies,
Orange Reversing valve Energize to cool (Changes from heat to cool on heat pumps)
B Varies,
blue, black
brown, orange Sometimes common side of transformer. Needed on some electronic thermostats or if you have indicator lamps
OR
Reversing valve (energize to heat) above. York and Trane sometimes use (B) as common. Might be heating changeover or on older stuff common of transformer.
X Varies SEE NOTES BELOW Might be common but sometimes emergency heat relay
X2 Varies Second stage heating or indicator lights on some thermostats Might be emergency heat relay
T Varies,
Tan or Gray Outdoor anticipator reset Used on GE/Trane/American Standard and some Carrier Products.
L Varies Service Light

Turn the power off going to the unit. Take the cover off and give us a pic of where the low voltage wires hook up. Good job with the first pics but we need to see what the low voltage wires(thermostat wires) are going to.