Fan stops and starts before reaching temp and compressor continues running. No Common Wire

[EliasI]

@CoolingWizard I have seen how helpful you are to the community and I am hoping you can help me please.

On AC mode, the blower stops and starts here and there before the thermostat reaches temperature. In other words, the thermostat shows blue and the compressor continues running but the fan stops and starts.

Also, if I am running the fan alone and I drop the temperature, when compressor kicks in, also the fan stops for a blip then starts again with compressor.

I read another post that adding a common wire can help solve the issue. The reason I was hesitant because the system has also a humidifier and the Green (G) wire does not connect to the HVAC main board and it it connected from Nest to Humidifier directly (see attached link/pictures HVAC and Nest Wiring) and Gf from humidifier is connected to G to HVAC and I was hesitant to mess around before consulting with you on wiring.

1. Does the current wiring in attached link look right to you?

2. Do you expect adding a common wire to solve the issue?

3. If so, how should I rewire considering how the green wire goes from Nest to Humidifier (see attached link)? Am I safe to keep all wiring the same and simply add a wire from HVAC (C) to Nest (C) and keep everything else the same?

Side note: My understand is to use the humidifier in winter and current settings are blower OFF and Manual so I don't know if that's affecting the G wire and the fan going in and out. 

Thank you for your help!

Elias

HVAC and Nest Wiring  

[CoolingWizard]

@EliasI ,

Let us see if I can help you.  Your fan “issue” is the Humidifier controller.  The humidifier receives R, C, Y, G, and sends Gf to the Air Handler.  Your humidifier controller should be left in Auto mode, and all you do is set the desired humidity level. Typically about 25 to 30%.  The humidifier receives the call for fan from the thermostat (G) and then is supposed to pass G to Gf. The humidifier has control of the fan so of the air is very dry, it can, in automatic mode, turn on the blower and do its job.

In manual mode it will interrupt the fan signal while it resets itself when W or Y calls. 

place your humidifier into automatic and leave it there and it all should solve your problem

AC Cooling Wizard

[EliasI]

Thank you for your detailed and quick response.

Which setting do you think could solve my issue?

A. Putting humidifier in Auto

B. Blower Activation On

C. Both of the above

I switched the humidifier to Auto and Blower Activation to On (still checking if that solved the issue or not) but now I am getting an E3 error on the humidifier.

On another note I put the heat ON and the humidifier doesn't work in auto. It only works in Manual.

How do you think I can fix the E3 error (while in Auto) and fix the fan issue (while in Manual)?

Is doing a C-Wire helpful at all in my case or do I not need it?

Thank you,

Elias

[EliasI]

@CoolingWizard Additional information to the above: The AC was just trying to drop temperature from 74F to 72F and after about 60-90 mins of running, the fan stopped for about 5-10 seconds and started again with Humidier Auto and Blower Activation ON. In other words, I am still having the fan stopping issue and E3 error on humidifier by setting it to Auto (please see paragraph above)

[EliasI]

@CoolingWizard @NestCommunity I am still having the issue and I would really appreciate your help. Please read the updates above and also last night it was running then stopped and I had a delayed start message (see picture in the folder link in my first post)

[EliasI]

@CoolingWizard I would really appreciate your help as I am still having the issue. Please see updates above

[Calvin4038]

Without going into too much detail, I have found that a MAJOR issue with the NEST system and most problems all come from the actual BASE PLATE.  I have two houses, both with Gen 3 systems on them. They both have TRANE AC handlers, and the first house had a different system before we updated it with a TRANE, but that NEST always worked perfectly. We have had issues with the second house from day one. Living in Florida and with as many lightning strikes as we get, the EMP it produces messes with many things.  The neighbor's house just got hit a couple of weeks ago, and the next day, we started to have problems with the NEST.  After paying our AC guys to come out and troubleshoot, they determined it was the NEST.  I bought a new one, pulled it off, and replaced it. But the same problem.  No C wire 

I turned it back in, and the AC company gave me a Honeywell Thermostat (That sucks, BTW). I then proceeded to go ahead and take apart the base plate, only to discover that most of the brains of the NEST are located in the base plate.  

NEST does NOT sell just the base plate, but I picked one up on eBay for $65, swapped out the base, and plugged it back in the NEST, which is working perfectly.  

Trane sells something very close to what NEST can do, and the only problem is its about $700 

I would suggest to anyone who is having these issues to buy a new base plate.

I hope this helps. 

[EliasI]

Can you please elaborate on what issues you were having so I could see if mine is similar or not? Did you attempt at all adding a C-wire or was changing the base and staying without a C-wire the solution for your case?

[EliasI]

@Calvin4038 I changed the base and it didn't solve the issue. Do you have a C-Wire? I wish someone could help with wiring C-wire with Aprilaire hunidifier, Nest and furnace diagram

[EliasI]

@AHawk21 I saw that you had a similar issue (please read updates above). Did your C-wire addition completely solve it? Does your system has a humidifier as well? Can you please describe your wiring?

[Calvin4038]

The wiring from the air handler and from the compressor was fine. The ac guy showed me using a volt meter. So no need to run another wire. 
my advice is to make sure your wires coming from everything is correct 

if it is, look at changing out the baseplate. 
if you remove the four small screws behind the baseplate, you will be amazed on all the electronics that are there. 

hope this helps

[EliasI]

@AHawk21 can you please see above? I would really appreciate some help

[Calvin4038]

Hi Eliasl, first question I have is do you have a common wire? If you do have one, what type of voltage do you see. 

The Nest uses the C or Common wire to CHARGE the internal battery. You can pull off the large controler from the base unit and charge it with a usb. Problem is that it doesnt last very long and more then likly it will say that you do not have a C wire installed. 

From what I have found out, the first Gen Nests didnt need a C wire, but the Gen 3 does.  

Nest sucks with parts BTW, I tried to order another base and they do not sell them, I had to get mine from Ebay, and I did choose a three year warrantly on it just in case. I swapped it out and everything works perfect.  

If you have a multi meter, you will be able to figure out if you have power from the C wire. 

I hope this helps. 

[CoolingWizard]

@EliasI , when you have an humidifier you end up turning full control of the indoor fan over to the humidifier.  Your call for fan from the thermostat goes to the humidifier (typically attached to G) and then sends the call for blower fan to the air handler from the humidifier Gf terminal.  Why is it designed this way?

That humidifier you have can operate independently of the HVAC system. When the humidifier is running in the Automatic mode, it can turn on the blower on if its internal humidistat detects to dry of air.  When the call for blower fan is sent from the thermostat, the humidifier receives the Call for blower fan on G, it is supposed to be internally connected to Gf. If you are having problems the problem is more likely your humidifier controller.  Here is how you can determine that to be the case. 
1. unplug or turn off the power to the humidifier. 
2. Open the cover of the humidifier humidistat.  
3. Remove the thermostat wire attached to G. 
4. Loosen the Gf terminal and ADD the G wire to the Gf terminal with the wire going to the blower fan. 
5. Turn power back on. 
6. Go to your Nest Thermostat and turn on cooling.  Does the blower stay on now?

AC Cooling Wizard

[EliasI]

@CoolingWizard thank you for getting back. I linked the G and GF directly to each other as you described and I am still having the same issue - Please see these pictures 

Question1:

When AC compressor kicks in

I noticed that VIN drops from 37V to 8V and Lin drops from 40mA to 20mA are these numbers acceptable or do I need a C-wire?

Am I able to connect Two C-wires coming from HVAC to both the humidifier and the nest thermostat at the same time or should C-wire only connect to only humidifier or Nest at a time?  See Nest Power information and wiring

Question 2:

Te humidifier shows an E3 when I had it in automatic. Can you please check my wiring in this link HVAC Wiring and provide me with your expertise?

With your help we can solve this before the issue gets worse - thank you!

Elias

[CoolingWizard]

@EliasI Here are your answers:

Answer 1. The key value is the battery voltage. The voltage is what is needed to activate the compressor.  The Vin is the input from the HVAC to the internal charging circuits.  The 40mA drop to 20mA is again input and remains acceptable.  Whenever it is possible, you should use a C conductor wire going to your thermostat.  Since you have only 4 conducting wires, you will need a Nest Power adapter or install a new thermostat cable that has 7 conductors. 

Answer 2: an ApriAire E3 error means the blower unit and the controller are not seeing each other.  That should not of happened by moving G wire to Gf. Lets see if there is some bad software in the AprilAire. Move the two fan wires to G in the AprilAire.  By the way, the AprilAire should have been installed with its own dedicated power transformer and not using the HVAC transformer power. 

If my responses help you to understand your problem, give me a Kudo down below. If my response solves your problem, please choose the Recommend this Answer. 

The AC Cooling Wizard

[EliasI]

@CoolingWizard 

Topic 1. I have no problem running a 5 or 7 wire and add C-wire. Am I OK to have the C-wire connected from HVAC to humidifier and from HVAC to Nest at the same time?

Topic 2. The E3 error has always popped up whenever I switched from MANUAL to AUTO on humidifier per your recommendation. The E3 does not occur if humidifier is on Manual. Also yes there seems to be a separate transformer for HVAC and for humidifier See transformer photo here 

Topic 3: All that being said, I feel that there is some wiring issue as I am seeing multiple posts online that use C-wire and the *pro wire feature on Nest for humidifier but that's not how it is currently installed.

Can you please check the current wiring in these pictures and recommend me how to rewire the system. A wiring diagram of Nest, HVAC and Aprilair humidifier is what I am looking for.

Thank you very much! I really want to get to a solution and press that KUDOS and recommend this answer button to help others!

[CoolingWizard]

@EliasI 

Topic 1 tesponse: If you have the ability to install a new 7-conductor thermostat cable between your Furnace and the Nest Learning Thermostat then I would highly recommend doing that. The C wire representing the Common side of the power transformer has to be the same as the R transformer. If there is indeed a separate transformer for the AprilAire there would not be a cable connecting to the Furnace control board.  A separate transformer would mean that the R and the C would come from the separate transformer, and the only other input would be a connection to the furnace G terminal.  

Your picture that shows the thermostat cables, shows that the humidifier is attached to the HVAC furnace control board. That being said, it is using the HVAC Furnace transformer. 

Topic 2 Responce: The E3 error is local to the AprilAire and needs further investigation. 

Topic 3 response: I will try to find time to draw a wiring diagram for you this weekend. 

AC Cooling Wizard