[Nlexi]

Bought a new basic Honeywell programmable thermostat but want to make sure I wire it correctly so I don’t damage anything. I just want to make sure of two things. My current thermostat (see picture) has a blue wire in “B” and an orange wire in “O”. The Honeywell thermostat does not have a “B” or “O” but just an “O/B”. From what I’m reading in the instructions, the blue wire attaches to “C” in the new thermostat but why then isn’t it in the “C” spot in the old thermostat? Does that sound correct? The blue wire in the furnace Panel is also In “B”.
Now how about the orange wire, does it go in the O/B in the new thermostat?
I have heating and cooling and assume by all my investigating have a heat pump. Help please, not sure if I’m reading to much into this or is it that simple. All other wires are self explanatory.

 

[roughneck]

Just before we get started, you should understand it’s ill advised to use a programmable thermostat on a heat pump.
If you do want a programmable thermostat, it’s best to use something that can lock out auxiliary heat.
Programmable power saving thermostats can have the opposite effect on an air source heat pump with electric backup heat, and raise your electric bill.

 

[user_12345a]

To have both O and B on a stat that has a C terminal - may very well have an old zoning system that modern stats are not compatible with natively.

 

[roughneck]

To have both O and B on a stat that has a C terminal - may very well have an old zoning system that modern stats are not compatible with natively.

Didn’t even notice the B. Good catch.

 

[Nlexi]

So I’m gathering that I should return this programmable thermostat. What would my options be for a new thermostat, have my hvac company install. I wanted to start with a new thermostat as my A/C is set at 78 but drops to 68-72. I read the thermostat could be the issue.

 

[user_12345a]

Well, lets figure out what kind of system you have first.

Do you have two thermostats controller one system? Zoning panel?

Can you post the full model of the outdoor unit and see where the o and b wires connect to on the other end?

 

[diyorpay]

Your existing thermostat was very versatile for many types of installation.

Your description of failure sounds like a battery issue. When thermostat loses battery, it reverts to a middle ground 'safe temp' temp like 68-72 for cooling and heating.

Test your batteries. A perfect condition with healthy batteries also requires the door to be closed properly, part of getting a good connection. If any old batteries had failed in unit and acid dripped onto terminals, result is poor connection. The batteries hold your settings. If you default to 68-72, you probably lost your hourly and weekend settings too? Check your batteries.

Since it's a bit old but well designed in its day, if you can get a 'C' wire to it, it would provide the 24V necessary to run unit. Batteries would then be a backup to save settings.