AC short cycles (<5s)

[crl1]

I installed my Nest last fall so haven't gotten a chance to have it control the AC yet. I just turned it on it is not able to turn my AC on, at least not for long. The AC hums and the fan spins, but then that stops after 2-3 seconds. Maybe 20 seconds later, the Nest tries again, with the same result.

I already checked the unit itself by removing the Nest and directly connecting Y1 to RH. The unit works completely fine.

Has anybody seen this?

[Patrick_Caezza]

@crl1 

Do you have the Google Nest Thermostat? The one with the mirror cover.

Does it have a C wire installed? One of the symptoms of needing a C wire installed is the unit short cycling.

[crl1]

@Patrick_Caezza No C wire. Yes this is a Nest. I can try swapping my G and C and see if that resolves it. 

[Patrick_Caezza]

@crl1 

Yes, you can try the swap the G to the C trick. Just be sure to do it at both ends. This is a good way to verify if the missing C wire is a problem.

If this solves the problem I do not recommend leaving it that way as you lose fan control. I would recommend installing a Nest Power Connector

[crl1]

@Patrick_Caezza that did not work unfortunately. Same short cycle situation - not even a short cycle really but almost the sound of the initial current inrush and the relays clicking on but then within a second or two it stops. 

oddly enough, even when I was in the original configuration with the G wire connected to G and nothing on C, the Nest auto-recognized the C wire as being populated as well. Any thoughts on that?

[Patrick_Caezza]

@crl1 

Just to double check, when you used the G wire you did move it to the C terminal on the control PCB in the furnace, correct?

Can you post a picture of the base wiring here?

[crl1]

@Patrick_Caezza  Yes I did as you mention - I used the wire on G and swapped it to the C terminal both on the Nest and the furnace controller. I don’t have a photo available but that does explain it. 

[Patrick_Caezza]

@crl1 

You said that the thermostat showed a C wire was connected even when it wasn't, correct?

Have you tried resetting the thermostat to factory defaults and setting it up again?

Which wires did you tell the Google Home app you had when you set it up originally?