Google Nest changed over to basic Honeywell now nothing works...

electronictofu

I had a Google Nest for about a year, and I didn't like it at all, it did quirky things. So I pulled it, and replaced it with a non-programmable basic Honeywell home thermostat. Ive done these before, simple, color-coded, red jumper, etc. Nothing works, no heat, no ac, and the fan also won't kick on. No burned fuses, reset the breakers more than a few times. Returned the Honeywell at Home Depot and tried the same basic unit that was programmable. Still nada.

When my HVAC buddy did some other work last year he put the Google Nest in as a little hookup. Im curious, when doing so would any wiring changes happen at the actual AC unit? Mine is ground mount not roof so that's easy access but I dont see much change. For kicks I tried a couple variations with the blue wire, and the red with and without the jumper, but no dice.

I am hoping some wires are just not coded right or he made a subtle change I can find. Photos attached, round is the Google Nest, and the other photo is a basic ol' thermostat from Home Depot (Honeywell).

I have a feeling the blue wire may be the issue?
I did put my AC Voltage Detector (the pen style) against each wire at the thermostat and Im getting no beeping or detection on ANY wire.... So the problem may be outside, or blew something? The AC fuse panel has 2 old style fuses "red light on when fuse bad" those are ok.... not sure what to check next.

JUGHNE

HW tstat may not use a common? Relies upon batteries only?

mattmia2

Disconnect the blue, it is a common, it would go to c if the t-stat had that. b is something else for a heat pump system. Make sure it didn't blow a fuse or trip a breaker at the furnace/air handler, make sure there is still 24vac between blue and red.

electronictofu

mattmia2 said:

Disconnect the blue, it is a common, it would go to c if the t-stat had that. b is something else for a heat pump system. Make sure it didn't blow a fuse or trip a breaker at the furnace/air handler, make sure there is still 24vac between blue and red.

I just popped off the thermostat and put my AC Voltage Detector at each wire (the basic one that just says if power is there/ for outlets) and I got no beeping on ANY wires. I turned off all my breakers and sub panel, and back on, and my AC has its own little box with two fuses "red light on when bad" but those are ok. My AC or Furnace may be when I have to check, but I know the least about.

mattmia2

If you're lucky there is a breaker or a fuse on the transformer in the furnace, if you're not lucky there is a fuse built in to the transformer that is not replaceable. Is the furnace disconnect turned on? Turn it off before you change the wiring because shorting it while working on it can also blow the fuse or breaker. Do you have an actual AC voltmeter? I would start with that between r and c on the furnace and work from there.

electronictofu

My AC is outside, ground not roof which is good. The Furnace is in the attic, I'll save that fun adventure for last, it's a tight space for sure. Here is my AC unit, all these wires have power going here, but not leaving here. Is this the transformer?

pecmsg

The transformer is in the attic!

electronictofu

Gottcha. But can this part shown be bad? I have power going into it. But I tested the wires coming out towards the thermostat and nothing is coming out.

Jamie Hall

Note that a simple "beep" voltage tester may not beep for 24 VAC. Use a voltmeter. You should have 24 volts between R and W when they are disconnected from the thermostat. If you don't, either something is dead at the furnace or... the colours are lying to you.

pecmsg

electronictofu said:

Gottcha. But can this part shown be bad? I have power going into it. But I tested the wires coming out towards the thermostat and nothing is coming out.

Noncontact voltage testers are dangerous. You need a meter to test.

JUGHNE

That is the AC contactor and has 240 volts going into it, it is a relay that when closed will run the compressor and outdoor fan.
Because the contactor is a single pole, every wire you see outside is "hot".

This is completely separate from the 24 volt which should come from the attic furnace/air handler.

The 2 side wires would be where the 24 volts would go to from the attic unit via the thermostat.

You may be in over your head and need help.

electronictofu

Thanks guys. Im being safe for sure, and hope to fix it myself, I lost the number of a buddy who could help me for next to nothing or free, which sucks.

My attic furnace photos.... I didn't see any visible fuses, burn marks, or anything obvious that I could pop out and in. There is a 120 style wall plug above the furnace, no switch on it, or fuse, or burn marks, just a normal plug.

Could potentially still be wiring mixed up, I hope.

Any know what's next" Id love to try a couple more things before calling someone out, this guy is broke as a joke....

pecmsg

Top of the circuit board is a purple car type fuse. 

JUGHNE

Yes, first picture top left is your fuse, 3 amps.

Isolate the blue at the tstat. Install new fuse. Close blower door.

The tstat could be toast as one of the switches may have handled a direct short that blew that fuse...hopefully not the transformer.

Jamie Hall

Almost all of the wiring you are taking pictures of -- except the thermostat -- is either 120 or 240. That can ruin your whole day if you start playing with it without knowing exactly what you are doing...

EdTheHeaterMan

pecmsg said:

The transformer is in the attic!

And how on earth did this happen? Someone has taken the thermostat you despise the most and replaced it with your dear friend Honeywell.

So to be clear on what you did @electronictofu, you removed a thermostat that required a common to operate the onboard microprocessor (that means the thermostat consumes electricity produced by the transformer in the furnace) in order to do what old school thermostats just did with switch contacts only (No C wire needed).

You then connected the switch contacts from R on the furnace transformer to Y on the furnace circuit board, and outdoor unit by way of the Honeywell thermostat. You also connected R on the transformer to G on the furnace circuit board by way of the Honeywell thermostat. Finally, you connected R on the furnace transformer to W on the furnace circuit board by way of the Honeywell thermostat. And if you stopped there, you would have had no problem.

But you continued to connect the common from the furnace transformer to the B terminal on the thermostat. That was your mistake. B on a Honeywell thermostat is usually used for heat pump operation to make the reversing valve switch from cooling to heating mode. That means there may be a switch that in fact connected the R from the furnace transformer directly to the Com (or C) on the furnace transformer by way of the Honeywell thermostat. That would be known as a direct short circuit. Good thing there is a fuse on the circuit board. That should have protected the thermostat, circuit board and the transformer from permanent damage.



Now get a new fuse from the auto parts store with the same AMP rating as the blown fuse (Purple = 3 AMP / Yellow = 5 AMP) then remove the Blue wire from the B on the thermostat and from the (C) on the circuit board. Replace the fuse and start the AC unit so you can beat the heat!

PS: @pecmsg would probably love it if you send him your old thermostat. He is a collector of them, He can't say enough about Nest thermostats. I will PM you his address so you can mail it to him. Send it postage due. LOL

HomerJSmith

You need a dual range pen circuit tester. https://www.homedepot.com/p/Klein-Tools-Dual-Range-Non-Contact-Voltage-Tester-with-Flashlight-12-1000V-AC-NCVT-3PR/312665549
However, the best test for voltage is a cheap digital volt-amp-ohm meter.
https://www.homedepot.com/p/Gardner-Bender-4-Func-14-Range-Manual-Digital-Multimeter-GDT-3190/202867883
https://www.harborfreight.com/11-function-digital-multimeter-with-audible-continuity-61593.html

pecmsg

and why is it always a NEST?

I don’t know!

HomerJSmith

pecmsg, because it always keeps you up a night, it's a conspiracy, I tells ya!

EdTheHeaterMan

pecmsg said:

and why is it always a NEST?

I don’t know!

Isn't this just the opposite of a Nest? Those Honeywells can be a real problem if you ask me!

Jamie Hall

I can remember when a thermostat was a temperature controlled on/off switch. So simple...

electronictofu

MY GOD, I didn't even see that purple fuse. I am praying that's it. I'll update soon, they're so cheap, I'll just buy one before I get back in the attic to check if that was it. It'll save me a trip to the nasty attic.

How did this happen? Someone said I connected the blue wire, that surely sounds like the cause. Also, I cut the thermostat wires without turning off my power, dumb dumb I know.

I'll update soon. You all rock, thanks for the help so far. Hope the fuse works, Im in Sacramento (triple digits this week)

Not to get off topic, but the Google Nest always turned on learning mode, no matter how many times I reset it, Id come home to blasting AC, and the Nest in order to use the house fan (which I use alot) you have to have AC/HEAT turned out, you can turn the temp up or down, but anyways, I just didn't want the tech and got sick of it. Also it was expensive and I needed some extra cash so I sold it and went simple, which isnt always better, but yeah, we don't need to go there!

mattmia2

You should turn the switch at the furnace or the breaker to the furnace if you don't want to go up in the attic before working with the thermostat wires in case you accidentally short something out.

The control power for the condenser comes from the furnace, the furnace sends 24vac out to the condenser to close the contactor(relay) in the condenser.

pecmsg

HomerJSmith said:

pecmsg, because it always keeps you up a night, it's a conspiracy, I tells ya!

No

simply
NEST 

S
U
C
K
S
!!!

HVACNUT

electronictofu said:

MY GOD, I didn't even see that purple fuse. I am praying that's it. I'll update soon, they're so cheap, I'll just buy one before I get back in the attic to check if that was it. It'll save me a trip to the nasty attic. How did this happen? Someone said I connected the blue wire, that surely sounds like the cause. Also, I cut the thermostat wires without turning off my power, dumb dumb I know. 

You basically stuck a fork in the toaster. By either connecting Blue to B, you sent 24 volts direct to ground, or by not shutting off the power before cutting across Red and Blue. Again, direct short.
No Blue wire on the Honeywell. Disconnect Blue from C in the furnace also but leave the White wire connected to C.
Pick up a few spare fuses. 

electronictofu

I ditched the blue wire at the furnace and at the thermostat, and it WAS that dang 3amp fuse! You guys nailed it. Im back up and running.

Thanks everyone for your time and help.
-P

HomerJSmith

Those little purple fuses ain't cheap. That's why I use a Lil Popper, 3 amp when testing.

mattmia2

HomerJSmith said:

Those little purple fuses ain't cheap. That's why I use a Lil Popper, 3 amp when testing.

put a 24v or 2 12v lamps in series with it, the lamp will act as a resistor and keep the fuse from blowing while you figure out where the short is.

Jamie Hall

You may be able to find a 24 volt test light at NAPA p-- 12 volt ones are common. Use them all the time troubleshooting automotive gremlins.