Thermostat heats on call for cooling

[chipj]

After working great for two years now stays in heating mode and won’t cool… Defective thermostat?

[RomanandsonAC]

Need a bit more information to attempt help. Need type of system, electric heat, heat pump, gas heat, etc? need manufacture of equipment and model? 

[chipj]

Thank you!!

Switching O & Y is a great idea!!

I do have a volt/ohm meter though… how do I check continuity of O?

[Ryan_G]

Hi chipj,

Thanks for reaching out and we're sorry for the delay.

Though we don't have any specific steps on how to check the continuity of O, you could check and test your system using this link.

Also, changing the O/B orientation is a good test to know if the valve is working.

I hope it helps,

Ryan

[chipj]

Sorry. Yea, of course. Carrier Hp system CH14NB036

[RomanandsonAC]

So your thermostat is set to cooling and heating, or can not be set to cooling

[RomanandsonAC]

You have a 14 seer 3 ton heat pump carrier system, are both the air handler and condenser running?

[chipj]

Yes both run but the reversing valve does not switch to cooling when thermostat calls for cooling like it has for the last 2 years…therefore it heats rather than cools..I’ve already checked all low voltage connections in the stat and at the air handler and at the heat pump..if I jumper O & Y outside reversing valve switches and unit then cools. 

[RomanandsonAC]

If that is the case then the thermostat is not sending control voltage out of O to energize the changeover valve. By you jumping out O & Y you have just done what the thermostat is supposed to do. One other way to validate is with a volt ohm meter. You should receive 24 to 28 volts with the system set to cooling wired to O. Between the C wire(normally blue wire) and the Y, and between the O and C wire. If you do not have voltage between C & Y and C & O, then you either have a faulty thermostat, or an open O wire.  If your thermostat wire has extra conductors you could take the O wire off and change it to one of the spares, at the air handler and condenser. So if you have a spare wire switch what you have on O to the spare. 

Here are the schematics of your Carrier unit with a standard HP thermostat

[RomanandsonAC]

Let me know if you have spare conductors on you thermostat wire feeding the condenser

[chipj]

No spare wires… if stat is defective can I switch w another stat not base to check it? 

[RomanandsonAC]

If the stat is defective i believe they have a 3 year warranty, however before going through taking it off the wall and heading to the retailer to exchange the stat. At the condenser you said the if you jump the O & Y the change over valve switches over. If that's true, only two thing will keep it from shifting to cooling when set. One the stat may be faulty, however the thermostat O(orange wire) may also be open or broken. One way to check if you don't have a volt ohm meter is the reverse the orange and yellow wire at the thermostat and the condenser. If the Orange wire is good, the unit will call and start. If it isn't good, your change over valve will switch when calling for cooling, but the unit won't run. This maybe the best way to validate the thermostat being faulty, and the O pin is not sending voltage to engage the changeover valve.

[Jonm]

This is the second thermostat I’ll have to change due to the o circuit not engaging.

[chipj]

Thanks for your comment!

how did you go about exchanging it in warranty? 

[Ryan_G]

Hey chipj,

Thanks for sharing your thoughts here in the community.

Could you tell us if you already tried checking or changing the OB orientation from the thermostat settings?

Regards,

Ryan

[chipj]

yes.  After jumpering outside and the cooling mode operated perfectly.. it seemed the sub base was defective. Particulations at work perfectly up into that point. So I contacted Nest and got them to send me a replacement thermostat, replaced it and all working back to normal. It seems a lot of needless diagnostic work knowing that I was working perfectly and then all of a sudden was not and I could jump right outside and get it to cool properly.

[Ryan_G]

Hey chipj,

Thanks for the reply and it's great to hear that your system is now back up and running. We'll leave this thread open for the next couple of days and let us know how it goes.

Regards,

Ryan

[Ryan_G]

Hey chipj,

I just wanted to follow up and see if you're still in need of help. Please let us know as we would be happy to answer any questions you may have. 

Best regards,

Ryan

[chipj]

No, all working great now!

thank you! 

[Ryan_G]

Hey folks,

Thanks for visiting the Google Nest Community and thanks for the update chipj.

Since this thread hasn't had activity in a while, we're going to close it to keep content fresh.

If you have additional questions, feel free to submit another post and provide as many details as possible so that others can lend a hand. 

Hope this helps!

Kind regards,

Ryan