E79 nest thermostat leanring

[srhsieh]

I installed the nest thermostat.

My house has two zones -

The system worked well, until about two months ago,

The E79 error message showed up.

Within this community, I read some threads and decided to follow the system - turn off the furnace and then turn it back on.

This error disappeared, but then a few days later, E79 came back again.

Therefore, since then, I have been applying this strategy.

I then decided to contact the google support team.

One support staff suggested to disconnect C-wire from the thermostats.

The E79 did not not show up, but every now and then A/C will spin (like you clap fingers).

It is like A/C receives a signal but did not turn on.

I reconnect the C-wire and then contact the nest support team (and then been suggested to follow a link to all E79 error).

At this point, I am desperate. One one end, I feel that the nest thermostat is modern. But on the other end, I should not retire my conventional thermostat since they worked perfectly.

Need help.

Regards,

Henry

[zoeuvre]

Hi srhsieh, 

Thanks for posting here in Community and I'm sorry to hear about the situation. Please send us your Nest Learning Thermostat's power reading with and without C wire. 

• To open the Quick View menu, press the thermostat’s ring.
• Choose Settings.
• Turn the ring to highlight Technical Info then press the ring to select it.
• Select Power. 
  • VOC
  • VIN 
  • IIN

I'll look forward to your response.

Best, 

Zoe

[srhsieh]

Hi Zoe, let me give you an update;
I have the AC person came over and he connected the C-wire.

After this,  the C-wire issue disappeared, and I thought the issue is resolved.
Then 36 hours later, new message E74 shows up and then the entire system shut down (not working).
So I am waiting for the AC person to visit my home again to either undo what he did (correct what he think the C-wire), or figure out how to take care "no-power to Rh wire".
In the meanwhile, it you have any suggestion on E-74 or E-79, I am open for any suggestions.

With E-79, the system works (very interesting), but annoying.
With E-74, the system shut down. (no fun).

Before 'connection C-wire", the power reading was 3.91V (Battery), 36.23 V (Voc), and 36.23V (Vin).

It is the reading on the downstairs thermostat. The upstairs one, I did not have the chance to take a photo.

The current power reading on both thermostats are: upstairs 3.724V (Battery), 0.02 V(Voc), 0.002V (Vin), downstairs - 3..667 V (Battery), 0.01V (Voc), 0.01V(Vin).

There is no power to Rh wire.

Any suggestions?

The worst outcome is to undo what he did (to reach the E79 status, at least the system works), and then see if you help out.

Henry

[zoeuvre]

Hi there, 

Oh no! Thanks for getting back to us. Let's sort this out. 

Please make sure that your power breakers are on. Then, after you've made sure that they are on, turn off again the power to your HVAC system and then remove and reconnect your Nest Learning Thermostat wires.

Thanks, 

Zoe

[srhsieh]

Hi Zoe,

What you described in the email was exactly what I have been doing since early January.

1. breaker is on

2. turn off the power to HVAC

3. remove the thermostat

4. reconnect the thermost

5. turn HVAC power on

A few days later, E79 showed up again, then I repeated steps 1-3 but reconnect the wire (in particular C-wire), and then step 5.

A few days later, E79 appeared again.

Called the google support, Roy (from Philippine) suggested to remove the C-wire.

Therefore repeat steps 1-3, remove C-wire, and then step 5.

Before the HAVC gets activated, the A/C will spin a few turns (like you clap the fingers).

Reconnected C-wire, and then repeat power off/on HVAC and then wait for E79.

On the bright side, the E79 does not affect the functionality of furnace (ie, when the temperature reaches its setting, the furnace power on).

Besides, I am in California so I have time to sort this out.

So I posted this on community.

Regards,

Henry

[zoeuvre]

Hey Henry, 

Thanks for the follow-up and I appreciate you following the steps given by our contact support team.

I have validated all of the information you've provided, and the next thing we have to do is contact your AC technician again to make sure that the C wire is properly grounded because if the C wire is connected, you can hear clapping sounds from your AC unit, which is not normal, and when the C wire is disconnected, the Nest Thermostat shows no power to RH. 

We're here if you have any other questions.

Regards,

Zoe

[srhsieh]

Hi Zoe,
I had my HVAC guy step in a few days ago.
We believe that he had resolved the issue.
I am going to spare you with the details.
To be sure, I am going to wait for about 5 days to see if the issue is resolved.
If I do not get back to you after 5 days (knock on the wood), you can assume that the my E79 problem is fully resolved.
If by remote possibility, that E79 or relevant error message show up again,
I will email you.

Regards,
Henry

[zoeuvre]

Hey there, 

Sounds like a plan! In case you have an update about this matter, feel free to message again. We're here to help.

I'll look forward hearing from you again. 

Best regards, 

Zoe

[Jake]

Hey srhseih,

I wanted to check in with you. Are you still running into the E79 error? Let me know, as I want to ensure you are good to go, and everything is working properly from here.

Best regards,

Jake

[Jake]

Hey there,

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

Best regards,

Jake