Gen 3 Learning Therm - No error codes & no fan.

[DavidT1]

Previous thermostat wiringThis morning I replaced a simple 4 wire thermostat, R,O,Y,W, with my gen 3 and all went well following the instructions and wiring diagram. No error codes and it registered the wiring correctly in the app. When the AC started, the compressor came on fine, but no forced air fan action. Any ideas on how to make the fan work?

P.S. This evening I put the previous thermostat back in and the fan came on.

[DavidT1]

Hey @CoolingWizard, Any chance you have any ideas on this?

[CoolingWizard]

@DavidT1 , since your old thermostat cable only has 4 conductors you are somewhat limited.  When in heating mode typically the furnace will control the blower fan. 
Since it appears that you have a heat pump system, you need to make you fan come on anytime the compressor is running. In your indoor air handler, you will need to put on a jumper wire between Y1 and G. 

What part of the country do you live in?

AC Cooling Wizard 

[DavidT1]

@CoolingWizard , Yes, I just moved into this place a few weeks ago in the San Diego area, so I'm not familiar with the system, but was told it was a heat pump.
Thank you. After reading many posts, it did leave me curious about not finding a wire at G. I will try that tomorrow morning, as it's too hot today for it not to work right out of the gate, and reply back.

I appreciate your obvious wealth of experience and knowledge.
David

[DavidT1]

UPDATE:
It's been really hot. I haven't had a chance to add the jumper and reinstall the thermostat. Looking to do it later this week.

[CoolingWizard]

@DavidT1 , I live in Imperial County so I am about 90 minutes away from you.  Know that I can assist you on getting this working for you.  

AC Cooling Wizard

[DavidT1]

@CoolingWizard , So my resolution was to create a jumper at the thermostat instead of at the air handler as they are electrically the same, but the fan did not come on as configured in the attached image. What am I missing?

I did wrap the connection with electrical tape before installing the thermostat.

Follow up: I noticed the compressor keeps kicking on and then shutting off making a groaning noise, not previously ever heard. The app gives me an option to manually turn the fan on and when selected for 15 minutes, indicates that the fan is on while it is not.

I turned the system off through the app and pulled the thermostat and all seems quiet now.

Maybe some internal jumpers in the previous thermostat that I'm not accounting for?

Resolution

[CoolingWizard]

Let me see if I can help you to understand this. 
The thermostat only serves as a single control purpose.  That is to call for cooling, call for heating, or turn on the indoor blower fan. To achieve this the HVAC industry has standardized on the terminal identifier and its function. 
R,Rc and Rh. These are for 24V AC power input. The Y,Y1 and Y2 are  for Cooling. Y1 is Stage 1 Compressor on and Y2 is stage 2 Compressor on. Most HVAC systems are single stage compressors. Only the very high-efficiency systems use a two-stage compressor.  The W, W1, and W2 are for Heating. The W1 is stage 1 Gas Heat, W2 is stage 2 Gas Heat. For heat pump systems, W2 is defined as Auxiliary Heat. The G is for Blower Fan relay activation.  The O is for Heat Pump reversing valve for type  O heat pump systems and the B is the same for type B heat pump systems. Some smart thermostats will combine the O and the B together and just use software to set up whether the terminal functions as a type O or a type B. The C terminal is for 24V AC Power Common. Remember the control system runs off 24 V of AC power so think of the C as the neutral wire if that helps  

now the thermostat takes the input power and send it back to the HVAC system on one of the terminal wires. So what you have done by jumping the G with the Y wire is anytime the fan comes on. It’ll turn on the compressor if anytime the compressor turns on it would technically turn on the fan, but since you don’t have a wire running between the thermostat and the fan, all you’ve done is create a loop of power.  The jumper wire that you need has to be installed in the air handler itself. It cannot work by simply jumping the G to the Y terminal at the thermostat. So do yourself a favor and remove that jumper.
Your air handler will be in the attic, or an alcove closet on the main floor or possibly the garage or in the basement or in the crawlspace under the house. This is where a jumper must be installed between the G terminal and the Y terminal. I am not at all sure how your old thermostat was able to turn on the Blower Fan without a wire attached to G in the thermostat. 

AC Cooling Wizard

[DavidT1]

@CoolingWizard Yep, that makes sense. I see where I went wrong.  Jumpers at either end of the same Y wire actually have two different outcomes. My brain was out to lunch on that one. Thank you for the very detailed explanation. That definitely made things click in my brain. 

I'll go pull that jumper and put it on the other end, just as soon as I can find a ladder...

And I too am curious how the previous thermostat turns the fan on as well.

Again, thank you for your time and your clear and concise explanation.

[CoolingWizard]

@DavidT1 , when you get a moment, can you get me the Model Number of the outdoor unit? I want to pull out the installation manual and verify the configuration options. 

AC Cooling Wizard

[DavidT1]

@CoolingWizard 

Outside Heat Pump Model Number : 25HHA430A300

Outside Heat Pump Label

And in case you'd like the thermostat images...

FrontGuts

[CoolingWizard]

@DavidT1, you have a Carrier 2.5 Ton Heat Pump. I am not sure what part of the country you live in.  For very cold winters heat pumps systems need an electrical heat strips in the indoor air handler.  When get a ladder and are ready to go to your indoor air handler, you will need to locate the point where the thermostat cable enters the cabinet.  That will be the cabinet door you will need to open; you might need a 1/4” or 5/8” nut driver to remove the door screws. 
Also, see if it might be possible to pull in the wall a replacement 7-conductor or 10-conductor thermostat cable?

AC Cooling Wizard

[DavidT1]

Hello @CoolingWizard,

Thank you for all your time that you are putting into helping me. It is very much appreciated.

I live in San Diego, CA, so no, not very cold winters. The avg low winter temps are in the low 50's, with occasional dips into the mid to upper 40's. That said, the air handler may still have a backup heat strip. Cold is relative and subjective.

I am renting this place with a year lease. When I move out, maybe next Aug, would adding the 7-10 conductor cable still be compatible with the original thermostat?

And, can my Learning Thermostat be made compatible and operate correctly with the current 4 conductor cable if it is not easily, and retroactively compatible, replaceable?

Thank you

[CoolingWizard]

@DavidT1 , without a G wire attached to the old original thermostat, there’s absolutely no way for the system to work properly. Here’s why, when the thermostat controls an air conditioner the thermostat is required to turn on the air blower when it turns on the outdoor compressor for air conditioning. Now If you had say a gas furnace, when the thermostat calls for heating, it does not turn on the blower because the indoor heater control board has called a internal furnace control board. It is what will turn on the blower but it only turns it on after the heat exchanger reaches 274° that time it’ll turn the blower on, so there’s no cold air being sent into the house before the heat exchanger gets warm. 

To verify the old thermostat, put it back on there the way it was in there turn the air conditioner on, and I guarantee you the blower will not turn on.  

now, as to the replacement thermostat cable, keep in mind that it is simply a copper wire that lead from the thermostat to the indoor air handler control board. By replacing a four conductor wire with a 7 or 10 conductor wire gives you the capability to support any future thermostat or system upgrades. Doing this upgrade, since you are renting, is something that the homeowner or landlord should strongly consider doing. 

David, here are some little test you can try. Typically HVAC companies use the green wire for the fan and put it on the G terminal. What I’d like you to do is remove the green wire from W1 on your Nest thermostat, and carefully insert into the G terminal.   After that, turn on your air conditioner, and see if the blower turns on. If the blower does not come on, then go ahead and move it back to W1. It’s a blower indeed, as I suspect, it turns on you’re gonna be in good shape. 

AC Cooling Wizard

[DavidT1]

@CoolingWizard , That all makes sense about the G wire. I knew nothing about HVAC wiring before I commented here, but after just reading many comments, even I was confused about no G wire. After your explanation I am even more confused about it. But here's the thing, the original thermostat was working when I got here, with no G wire, I've swapped it out with my thermostat at least twice, and the original is currently installed, and every time, including now, the fan operates as expected.

I understand that adding more conductors gives you more options, but not knowing the equip well, I just wanted to make sure and not make any assumptions. If the existing cable is not too "stuck", or I can find a fishing tool for inside the wall, I may go ahead and swap it out at some point. Sooner than later if I can't get my thermostat to work on 4.

I'll reinstall my thermostat and try moving the W1 wire, green,  to the G terminal and see if the fan comes on with the compressor.

I'll update you when I get a chance to try that.

As always, thank you for your guidance with this.

[CoolingWizard]

@DavidT1 , Sometimes older thermostats have jumper switches on them to change functions. Since this thermostat has to turn the compressor on for either heating or cooling, the Blue wire in Y is always energized.  The white wire in the O terminal is energized for cooling and NOT energized for heating. By default your heat pump is a heater.  If the reversing valve coil fails, you still have heat. Most of the time us HVAC contractors try to install B models in the southern states so that cooling is priority and not heating. In the northern states they like old models so they always have a heater in the winter. But most southern states can get by in an emergency without a heater.   

For that reason there is no need for W1 wire. The HVAC industry defines the W1 as stage one heating on a gas heater. W2 is defined as stage two or as auxiliary heat when it’s connected to a heat pump.  
Since you were living in the San Diego area, there’s actually no reason to have auxiliary heat here so I believe that they reprogram the W1 wire to activate anytime that the compressor is turned on. I suggest you move that green wire to the terminal on the nest thermostat and see if it fixes your problem.

AC Cooling Wizard

[DavidT1]

Ok @CoolingWizard, I reinstalled the Nest Thermostat with the green wire installed at the G terminal. The thermostat freaked out for a minute warning that I was missing wires (see images). That said, the fan DID come on with the call to the compressor as you expected. I also turned up the heat to make sure it was functioning properly and the heat pump came on including the fan right away, but I don't know if the system heated up or not. Now, the thermostat read the room temp at 77 degrees, so maybe that's why no delay for the fan?

All appears to be up and running thanks to your sharing of your experience and knowledge, you know, unless you are concerned about the fan coming on right away with the heater.

Thank you!WarningSetupSensedCurrent

[CoolingWizard]

@DavidT1 , Your Google Nest Learning Thermostat is slightly confused. It thinks you have a duel-fuel system. You need to change the system type back to Heat Pump only since you do not have a gas furnace. 

It is normal that the blower fan should come on whenever the compressor is running. So that is OK. I am glad we got this working for you now. 

AC Cooling Wizard