Heating is working but colling is not working

[pronak]

My heater is working correctly but when i turned on ac it turned on and shut off instantly and showing ac will start again in 2 min after that same repeat telecast. So i can't use my air conditioner with thermostat. 

Have jumper wire with rc and rh but remove it 

I have this wire.

W C Y RC

[ZeroZero · Accepted solution]

I had the same or similar issue that when it turned off immediately after it turned on, the display showed "No Power".  As it turned out, my C wire, even though it's present, doesn't appear to have voltage (between R and C).  Once I disconnected C wire, cooling works fine and heating works still.  I guess I just need to replace the batteries more often.

[CoolingWizard]

You need to verify that there is voltage on the C wire. Use a volt ohm meter and check for AC voltage between R and C.  If not showing around 24Vac then the C wire might not be connected in the air handler.  

AC Cooling Wizard

[ZeroZero]

There is no voltage between C and R.  In fact, from what I can trace, C wire appears splitting from the R wire originated from the handler, while the Y wire at the thermostat is going through the outside unit and is connected to C terminal at the control board.  The Y terminal at the control board is not connected.  From what I've read, it seems a common problem between the old AC and the new Nest.  Some people said they fixed the problem by actually connecting the C wire from the thermostat to the C terminal at the control board.  To me, the thermostat works just fine without C wire.  The worst case I might have to replace the batteries more often, but that seems still the lowest risk.

[pronak]

Thanks!! It's working 

[Markjosephp]

Hello everyone,

I wanted to ensure that everything was covered here.

Thanks for looking into this, @CoolingWizard.

@pronak, I appreciate your update. I'm glad to hear it was sorted out. If there’s anything else we can help you with, please let us know.

@ZeroZero, your common wire may not be properly grounded, so the system uses power sharing but doesn’t get enough energy. It would be best to inspect its wiring connection within your HVAC unit to ensure that it's getting the power it needs.

Regards,
Mark

[Markjosephp]

Hey ZeroZero,

I'm checking back in. How's it going? Still need our help? Let us know so we can move forward.

Best,

Mark

[Markjosephp]

Hi ZeroZero,

It has been a few days since your last reply, and we're going to lock the thread within 24 hours. If you have any questions, please feel free to create a new post.

Thanks,

Mark