NEST Runs fan but wont turn on compressor

[Jdub014]

So I have recently installed NEST 3rd Gen thermostat.  My home has a separate furnace for baseboard heat which works perfectly fine.  And a separate AC unit in the attic.  I put the wires into the plate the same as they came off the old thermostat but it did not have a C wire.  So a C wire was then utilized.

W1 RH works perfect for heat.

Y1 G RC AND C for the AC- fan only mode works and kicks on fan, but when "cooling" is selected only the fan comes on and compressor does not kick on.  While running or not I viewed power which was 3.9 and 37.xx on the other two while running and approx 42.xx while off.

I am at a loss and not sure what to look at, any help is appreciated. 

[Jdub014]

Should include that outside compressor has power, capacitor is good, contactor functions.

[CoolingWizard]

You should be very careful when checking that voltage and know what the heck you’re doing. that power is  240 V AC at 50 A and will kill you in a fraction of a second if you stick your hand where it does not belong. Most HVAC systems which are split, air handler indoors, and the condenser outdoors, have a control board that when the signal of the wire (Y wire) arrives at the air handler, the control board is what turns on the blower fan not the G wire. 

now an HVAC technician would check for this problem by checking for voltage, arriving at the outdoor unit contactor coil. Voltage is present at the coil, and the coil has the contactor engaged, and the unit does not start, then they would investigate source power. As you stated, Check the Circuit Breaker, if the service disconnect is fused, check the fuses.  You will need a AMP Clamp meter to check the system; a multimeter will work for checking the contactor coil and the fuses.  

The AC Cooling Wizard

[Jenelyn_O]

Hi there,
 

Thanks for reaching out. I hope  you get the answer you're looking for. You can visit this support article for more information. Please let us know if you still have questions or concerns, as I’ll be willing to assist you from here.
 

I appreciate your help, @CoolingWizard.
 

Best,

Jenelyn

[zoeuvre]

Hey there,

Before I mark things as resolved, I wanted to check and see if there might be anything else you needed on this or to see if you had any other questions. If there's more you need, just let us know.

Thanks,

Zoe

[zoeuvre]

Hi Jdub014, 

We haven’t heard from you so, I'll go ahead and lock this thread within 24 hours. If you run into any more issues in the future, please feel free to create a new thread.

Regards, 

Zoe