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I changed an old thermostat that had separate o and wires…

Customer Question
Hi- I changed...

Hi- I changed an old thermostat that had separate o and b wires and the new one only has o/b and I'm not sure where to connect the extra wire

Contractor's Assistant: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?

The thermostat was flickering so I believe it is isolated to the thermostat

Contractor's Assistant: Do you plan on doing the work yourself?

Not 100% sure

Contractor's Assistant: Anything else we should know to help you best?

The compressor outside will not turn on

Submitted: 11 months ago.Category: HVAC
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Answered in 20 minutes by:
8/4/2017
HVAC Technician: airheatman, HVAC Technician replied 11 months ago
airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 9,203
Experience: Furnace, A/C and heat pump specialist.
Verified

If your old thermostat had both and O and B used , the B was common.

So wire that went to B wll go to C if new thermostat has a C.If no C, tape B off. Wire that went to O will go to O/B

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Customer reply replied 11 months ago
There is a white wire in c already
HVAC Technician: airheatman, HVAC Technician replied 11 months ago

Lets start from beginning.Tell e what color wires went where on old stat and model on old

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HVAC Technician: airheatman, HVAC Technician replied 11 months ago

OK lets go to air handler and see if maybe the brown B wire or the Blue B wire s loose (not connected) to anything. You can not have both a B and an O connected as that is the reversing valve control.B reverses in heat mode and O reverses in cool mode.

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Customer reply replied 11 months ago
I'm not seeing any loose wires
HVAC Technician: airheatman, HVAC Technician replied 11 months ago

Tell me what the blue and brown connect to

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Customer reply replied 11 months ago
Blue 01 brown B1
HVAC Technician: airheatman, HVAC Technician replied 11 months ago

What is model on unit where they are connected so I can pull a manual

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Customer reply replied 11 months ago
Mastertrol Mini 3
HVAC Technician: airheatman, HVAC Technician replied 11 months ago

OK that is a zone board. Looks they have configured the O and B to control zones,rather than reversing valve.Not familiar with this zone system.I have opted out of the question to see if perhaps other experts may have more information and can assist.Please do not rate or reply as that will send question back to my desk and delay getting assistance..Please stand by to see if another expert can assist.

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