Looking for wiring help with old to new thermostat


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Old 04-04-16, 09:46 AM
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Looking for wiring help with old to new thermostat

Hello.
I bought a new thermostat (Honeywell 5-1-1 programmable Model #: RTH7400D1008). My old one was a dial mercury thermostat. The wiring on the old one was:
Red wire to red terminal (see attached image)
Green wire to green terminal
Yellow wire to yellow and white terminal (jumper)
Blue wire to orange terminal

Do I need to add a jumper from the yellow to the white on the new thermostat?

There are black and white wires tucked into the wall, however, the white wire looks like it was used previously since it has the hook like it went around a screw.
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Thank you for any assistance I can get.
 
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Old 04-04-16, 01:19 PM
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What type of system are you trying to control,is it a heat pump?,it's odd to have W&Y jumped.can you tell where the white and yellow are connected at the airhandler?
 

Last edited by Geochurchi; 04-04-16 at 01:25 PM. Reason: More questions
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Old 04-04-16, 02:03 PM
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Looks like a heat pump setup without backup electric heat.
Can you post the model number for that thermostat. It should be on the back of the stat.
 

Last edited by PJmax; 04-05-16 at 10:10 AM. Reason: typo
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Old 04-04-16, 02:51 PM
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Thank you for the response. I am at work and I am going to look in the handler tonight. Will repost tomorrow.
 
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Old 04-04-16, 06:14 PM
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I have retraced the wires coming from the handler
Y=Y & W
O=B
R=R
G=G
No white, no black, no brown
This is a heat pump system.
The new thermostat has R & RC jumpered
 
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Old 04-04-16, 06:21 PM
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You have a heat pump with no Aux heat. I have seen that old T87 round Honeywell thermostat wired this way many times.

Geo units do not use Aux heat in my neck of the woods but I have seen quite a few posters in Arizona and Florida that have standard heat pumps without Aux heat.

The jumper between Y and W is not required on the new thermostat.

Blue = O/B
Red = Rc and R
Green = G
Yellow = Y

You must also configure the new thermostat for single stage heat pump.
Set function 170 to 2.
 
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Old 04-04-16, 07:26 PM
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That did the trick. Thank you!
 
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Old 04-04-16, 09:54 PM
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Glad to be of assistance
 
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Old 04-05-16, 05:36 AM
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Houston, just curious how that works,what controls which function the HP is supposed to be in,i.e. heat or cool.
 
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Old 04-05-16, 06:49 AM
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The O/B terminal controls this.
 
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Old 04-05-16, 09:19 AM
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Got that, but does the Y/W jumper function?
 
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Old 04-05-16, 10:11 AM
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This function is handled properly by a stat that controls a heat pump. The old Honeywell stat was not designed for heat pump use.

In order to get a heat pump to work in heat mode you just need to power the condensor with no reversing valve. So the W to Y created a connection that when W was active for heat..... Y only was active.
When in A/C mode.... Y and O are active.
 
 

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