Old heat pump with no C wire NEW WIFI thermostat installation

Old 05-11-14, 08:22 AM
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Old heat pump with no C wire NEW WIFI thermostat installation

I have an old Trane heat pump package unit with aux heat from the 80's with the original manual thermostat.
I just bought the Honeywell RTH8580WF thermostat.

The original thermostat I don't see a C wire. There is no extra wires available that I see at the thermostat all 8 wires are connected.

I was hoping someone could give me some advice on how to hook it up without having to run an extra wire.
Is there a wire I don't need on the new thermostat?

The picture is of the old thermostat with the wires connected.

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Old 05-11-14, 09:10 AM
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B is your common on new stat. You will also need to go thru program setup. Tstat needs to be in setting mode. Example for ac program stat needs to be set in cool mode. You hold up/down temp buttons for maybe 10 seconds. Screen will flash and program screen will appear. There will be a large number and smaller number at bottom right corner. Smaller number will be a zero push up button changing zero to 1. This is heat pump cooling mode. Program to your comfort. I'm not sure of your stat but most come with mode switch on backside. Mode can be gas/electric heat or heat pump. Slide switch to heat pump. Program process will need be complete to utilize heat pump. If not programmed correct you get no signal to O which is reversing valve. A heat pumps norm mode is heat. O has to have power applied or you will get heat calling for ac. Be sure to secure all power sources as you rewire. This to make sure you don't short wires together and damage transformer inside electrical component area. This unit is 220 volts ac transformer steps down to 24. Take care and time as this voltage can and will KILL you. I assume no liability for info provided this is for data only and always call a pro if in doubt. Good luck.
Old 05-11-14, 10:31 AM
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I understand now that the B on old thermostat will be the C on new thermostat.

Quick question,
On the old thermostat I have a T wire which is the brown in the picture that will not be used on the new thermostat correct?

On the old thermostat there is a W wire which is white in the picture that will also not be used?
W says it goes to K on new thermostat but then it says not to use K.

All others match up with the same letters.

Just want to make sure those 2 will not be used if not where do they go?

Old 05-11-14, 11:02 AM
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R - red - R
T - brown - not used
O - orange - O
G - green - G
Y - yellow - Y
B - blue - C

X2 - black - E/Aux
W - white - not used

This is what I came up with. A little unsure of the black and white connections.
Houston, the forum pro, will stop thru later.
Old 05-11-14, 04:23 PM
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I'd wire as PJ has posted and then configure function 170 to 7.

Push system/ then hold the bottom square on each side of the center button for ~ 10 seconds to enter configuration mode.

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