topic Re: AC turns on and turns off immediately in Nest Thermostats

AC turns on and turns off immediately

Dan838792 — Sat, 01 Oct 2022 21:07:46 GMT

I'm replacing a regular thermostat with a Nest and having a problem in which the AC will turn on, but then immediately turn off (fan in the AC starts up but then turns off, you can also hear the switch click off). The blower fan keeps on for a bit but the thermostat starts counting down to when it will turn the AC back on. Once it counts down the system goes through the same cycle: AC turns on then off with the blower running for a bit. I reinstalled the old thermostat so that we can use the AC and i would rather wait to reinstall the Nest till i know what changes i should make (if i need to get some data from the Nest when it is installed, i can do that).

The old thermostat used Red (connected to RC, with jumper to RH), White (connected to W), Yellow (connected to Y), and Blue (connected to B) wires. I connected Red to R, White to W, Yellow to Y, and Blue to C on the Nest.

Thanks in advance for any help you can offer.

Dan

Re: AC turns on and turns off immediately

CoolingWizard — Sat, 01 Oct 2022 21:30:01 GMT

Dan838792,

To help you better, can you provide a little more information.
what type of HVAC system do you have?

-Heat Pump

- AC with Gas Furnace, Forced Air

- AC with separate Boiler baseboard / Radiators

What model and generation nest thermostat did you purchase to install?

What make and model is the old thermostat?

Thank you in advance,

Ken, The Cooling Wizard

Re: AC turns on and turns off immediately

Dan838792 — Sun, 02 Oct 2022 05:15:11 GMT

Ken, thanks for the reply.

We have AC with a gas furnace and forced air.

We purchased the basic Google Nest thermostat (not the Learning or E model).

The old thermostat is a White Rodgers (looks like model 1F72-151.

Dan

Re: AC turns on and turns off immediately

CoolingWizard — Sun, 02 Oct 2022 21:35:15 GMT

I need some clarification on your OLD thermostat. You said there was a Blue wire on B. That White Rogers typically has a O/B terminal and an C terminal. The O/B is used for a Heat Pump system. So, was the blue wire on C or the O/B screw?

The Nest might not be set up incorrectly. The first Nest Thermostat had a base plates that matched the color of the ring on the front display. The Nest E and all subsequent Nest Learning thermostats all have a white black plate.

For the equipment settings of the Nest, the Heating Fuel type is Gas, the heating type is Forced Air. Make sure that you are not using ECO or any schedules yet. When you finish setting up the equipment. You have the opportunity to TEST. Test the cooling and see if it stays on until you end the test.

Ken, The AC Cooling Wizard

Re: AC turns on and turns off immediately

Patrick_Caezza — Tue, 04 Oct 2022 05:17:35 GMT

Post a picture of the original thermostat's wiring.

When you were asked to select the wires being used in the Home app when you set it up. Which wires did you select?

Re: AC turns on and turns off immediately

Dan838792 — Thu, 06 Oct 2022 01:09:46 GMT

Ken and Patrick, thanks for the responses. Sorry i haven't been able to answer your questions till now. Here is a photo of the old thermostat. (Full disclosure, I didn't record the wire locations before I originally disconnected them. I re-installed this thermostat by memory and it seems to be working fine for AC.)

Under the yellow wire is a Y, there is not a terminal labeled C or O/B (the red jumper connects RH and RC).

I also included a photo of the backplate of the Nest. As i mentioned in my original post, i inserted the red wire in the R terminal, yellow wire in Y, white wire in W, and blue wire in C. As i recall, i selected the W, Y, R, and C wires during setup.

Dan

Re: AC turns on and turns off immediately

CoolingWizard — Thu, 06 Oct 2022 23:40:13 GMT

Dan838792, I do not recognize your old thermostat, however the way it is currently wired in the picture, you have WHITE wire on W, a YELLOW wire on Y, a RED wire on Rc with a jumper to Rh, and a blue wire on B.

It is surprising that you do not have a wire on the G terminal. The G terminal is what is used to control the blower fan. Your fan has an AUTO mode and an ON mode. This is controlled with the G terminal. If your old thermostat used to allow you to switch the switch to ON, and the blower would come on, then there’s a wire that’s missing or that’s where the BLUE wire was connected. Now if the blue wire was indeed on the B terminal then don’t move it to G.

You can verify if indeed the blue wire is the common wire using a volt ohm meter. If you take a voltohm meter and set it to AC voltage, touch one lead to R, and the other lead to B and see if you get 24 VAC +/- 3 VAC. If you indeed find the AC voltage there, then blue wire is indeed your COMMON wire. If you see 0L or zero voltage, then in all likelihood the blue wire is your fan control wire.
If you do not have access to a Volt ohm meter, do this, remove the batteries from the thermostat, and wait about five minutes to see if the display remains lit. If the display stays on and does not go blank, then your blue wire is the COMMON wire. If the display in deed goes blank, then the blue wire is not the COMMON wire

Ken, The AC Cooling Wizard

Re: AC turns on and turns off immediately

Dan838792 — Fri, 07 Oct 2022 00:56:44 GMT

Ken,

I get 26.4VAC between the red and blue terminals.

if I flip the FAN switch from AUTO to ON, nothing happens.

The wire bundle coming out of the wall does have a brown wire, but it is wrapped around the sleeve and was not used on the old thermostat.

Dan

Re: AC turns on and turns off immediately

CoolingWizard — Fri, 07 Oct 2022 01:15:26 GMT

Dan, that blue wire is indeed your common wire, but unfortunately your HVAC contractor did not install a wire to be connected to the G terminal. What I can do is help walk you through how to use that brown wire conductor as your blower fan control and attach it to G on both ends.

Ken, The AC Cooling Wizard

Re: AC turns on and turns off immediately

Dan838792 — Fri, 07 Oct 2022 13:44:13 GMT

Ken,

Your help is greatly appreciated, thanks. FYI, here is what the wire bundle coming out of the wall to the thermostat looks like.

Dan

Re: AC turns on and turns off immediately

CoolingWizard — Fri, 07 Oct 2022 21:05:04 GMT

Do you have access to the HVAC system? That is, the air handler with the heater system? If so, We can hook that brown wire up as your FAN control. You will need to go to the indoor unit, disconnect the power (turn breaker off), open the access door, follow the thermostat wire, find that brown conductor, and if not connected, connect it to G terminal,

Ken, The AC Cooling Wizard

Re: AC turns on and turns off immediately

EdwardT — Tue, 11 Oct 2022 15:19:30 GMT

Hi folks,

@Patrick_Caezza and CoolingWizard, we always appreciate the help!

@Dan838792, how's it going with your Nest Thermostat? Were you able to follow the steps provided by CoolingWizard? Let us know if you have questions and we'd be glad to assist you.

Thanks,

Edward

Re: AC turns on and turns off immediately

Dan838792 — Thu, 13 Oct 2022 12:37:16 GMT

Ken,

Thanks for the follow up. i apologize for not touching base sooner, but i've been too busy and now i'll be out for a week. we do have access to the system so i'll try to get back to this in a week and let you know what i find.

Dan

Re: AC turns on and turns off immediately

EdwardT — Thu, 13 Oct 2022 16:34:54 GMT

Hi Dan838792,

Thanks for the update. I'll keep this thread open until you get the chance to try the steps.

Thanks,

Edward

Re: AC turns on and turns off immediately

Jake — Tue, 18 Oct 2022 18:01:13 GMT

Hey Dan838792,

I wanted to check in with you, and see if you were able to try the steps. Please let me know if you have any questions from here, as I would be happy to take a closer look.

Best regards,

Jake

Re: AC turns on and turns off immediately

Jake — Wed, 19 Oct 2022 18:01:19 GMT

Hey Dan838792,

I wanted to check in, and let you know that I will be locking the thread in 24 hours.

Best regards,

Jake

Re: AC turns on and turns off immediately

CoolingWizard — Thu, 20 Oct 2022 00:05:56 GMT

I know he has been very busy, can we please keep this case open for at a minimum 10 more days please?

Ken, The AC Cooling Wizard

Re: AC turns on and turns off immediately

Dan838792 — Thu, 20 Oct 2022 18:54:00 GMT

Ken,

I'm back.

Here is a picture of the wiring at the furnace. i circled the wire bundle (on the right) and then where each of the wires is attached. if it isn't clear, the order from top to bottom is Blue (to terminal G), white (to terminal W/W1), yellow (to terminal Y/Y1), and red (to terminal R).

Re: AC turns on and turns off immediately

CoolingWizard — Fri, 21 Oct 2022 02:43:55 GMT

Here is what I would recommend. Turn the power off to the furnace air handler. On the furnace, move the blue wire on the G terminal to the C terminal and keeping the other red wire going outside to stay there on the C. Then, uncoil the Brown wire and attach it to the G terminal. At the thermostat, uncoil the brown wire and attach it to the Thermostat G terminal. Turn the power back on, and then test the thermostat FAN switch to see if when placed from AUTO to ON and see if your thermostat turns the blower on.

Now, switching to the NEST. Restart the installation choosing the terminals I use as R, C, G, Y, W. Since the C was actually not attached, this will help straighten things out. Complete the installation and report back if the NEST starts behaving correctly.

Ken, The AC Cooling Wizard

Now, test your old Teri state and the FAN switch

Re: AC turns on and turns off immediately

Dan838792 — Fri, 21 Oct 2022 17:16:32 GMT

Ken,

That seems to have been just the trick. The AC is running now and i can control it from the app. (Now i just need to make sure my wife can control it from her phone since she was the one who wanted the Nest in the first place.)

Thank you very much for you help. I couldn't have done this without your advice!

Dan