Hi. My current system (Heat pump w/ Em Heat - Coleman) has the following 8 wires: B,0,L,X,W2,R,Y,G. I purchased a new Honeywell thermostat (RTH7600D1014 - touch screen model) which only has 1 O/B connector. I followed the instructions in the installation manual and connected the B wire to C, O wire to O/B, X wire to E, W2 wire to AUX. The rest of the wires I connected to the respected connectors. When I turn on the system, it only cools the house and the heat does not come on despite turning up the temperature. Honeywell says this has to do with the fact that my system has a separate O and B wire. Is there any way to work around this? Or to modify my existing system to work with the thermostat?

Have you checked function 170? You may want 7. Did you also check 190 to be sure it energizes the reversing valve correctly for your HP? Some HPs energize the reversing valve different.

Just in case, do you have the old tstat around?

Function 170 was already set to 7. and 190 was set to 0. My system has a separate O and B wire, but at the thermostat there's only 1 O/B terminal. I originally thought B was common, but I've checked and the X wire is the common.

I still have the old thermostat. I had to put it back on so that we can have heat. What info would you like on it?

Thank you for your help!

It's a good thing you kept the tstat. Fastest way to find out is map out what is energized on your old tstat. Run it through its paces and see what is energized in heat, cool, them heat, fan only, etc. Should be a easy since you now know what is common. Note that when going from heat to cool you there may be a time out lock out of up to 5 minutes.

What's the old tstat and HP? You may still need to set 190 to 1 depending on which mode your reversing valve is energized in.

It's an old Coleman dual mercury thermostat. I'm not home at the moment and cannot access my heat pump. I believe it's Coleman as well. The part number for thermostat seems to be non-existent. It's 3AAT83D13C1. There is no other number on the sub-base. The furnace is a Chromalox HAF-324D which is about 15 - 20 years old. I have not yet tried function 190 at 1. Maybe I'll give that a try.

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Originally Posted by mdupls

It's an old Coleman dual mercury thermostat. I'm not home at the moment and cannot access my heat pump. I believe it's Coleman as well. The part number for thermostat seems to be non-existent. It's 3AAT83D13C1. There is no other number on the sub-base. The furnace is a Chromalox HAF-324D which is about 15 - 20 years old. I have not yet tried function 190 at 1. Maybe I'll give that a try.

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3AAT83D13C1 This is a old GE/Trane thermostat part number. Back then Trane and Coleman trermostats were made by GE.

Below is a old road map to the terminals.
Check out the Trane wiring table

We actually had it set up like the Trane, with B as common and X as emergency heat. This set up did not work. Heating did not work and neither did emergency heat. Later I found that X was actually common. Apparently there's another make White Rodgers for tstats. They have a separate O and B terminal for heating and cooling. If we were to purchase a White Rodgers heat pump tstat (1F95-1277) will this work on our current system? I feel this is a better way to go then modify my existing system.

Here is the install manual for the White Rodgers unit. Check it out.

http://www.white-rodgers.com/wrdhom/.../0037-6753.pdf

Here is a line diagram of wiring.

http://www.white-rodgers.com/wrdhom/.../0037-6808.pdf

Indoor or outdoor remote sensor also available.

http://www.white-rodgers.com/wrdhom/...6_pg0008_9.pdf

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Originally Posted by mdupls

We actually had it set up like the Trane, with B as common and X as emergency heat. This set up did not work. Heating did not work and neither did emergency heat. Later I found that X was actually common. Apparently there's another make White Rodgers for tstats. They have a seperate O and B terminal for heating and cooling. If we were to purchase a White Rodgers heat pump tstat (1F95-1277) will this work on our current system? I feel this is a better way to go then modify my existing system.

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As suspected you have two different actuators for heat or cool instead of the typical one. Order this SPDT relay and wire it to actuate either O or B. I just ordered two of the larger relays from these guys and it was a quick and smooth transaction. Should cost you less than another tstat. If you need help wiring it in just repost.

Those older systems were quite common at one time and I remember wiring my fair share. I have been down the relay road before but if you can afford the correct W/R (1F95-1277) thermostat I would just buy it. The relays can be made to work but it just adds another pain in the A$$ when other problems happen down the road.

Post back with your results.