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Nest 3rd Gen Turns on HVAC but not Fan

Tkeirnan
Community Member

Hello - When my tenant tries to get the system to cool, the screen turns blue, and the system outside turns on every minute but without the fan actually turning on. It runs for about 20 seconds. There is next to no output from the vents.  About a month and a half ago, a technician came out to fix a "found shortage on low site" which he replaced. At the time, he said the Freon, capacitor, and compressor were all checked and working fine. When this repair was done, the system seemed to be working fine immediately after, but its hard to tell if the fix lasted more than a week because the tenant is always away, travelling for work. Now that he has visitors staying over, he is expressing this issue. Please help. 

13 REPLIES 13

CoolingWizard
Platinum Product Expert
Platinum Product Expert

What happens is your system is detecting the extremely high superheat and extremely low sub cooling and that creates a refrigerant pressure problem.  The indoor fan needs to be serviced.  Contact a local HVAC service company and they can inspect the blower motor and determine why it is not turning on.  This is either a failed capacitor or a shorted out motor. 

AC Cooling Wizard

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Tkeirnan
Community Member

Hello. Thank you for the reply. Is this issue a consequence of the first issue? Did the technician do something wrong the first time, or is this a new, unrelated issue? Since it’s been more than 30 days since last visit, the technician wants to charge new service fee. Last time I paid $330! Thank you

CoolingWizard
Platinum Product Expert
Platinum Product Expert

@Tkeirnan ,

that actually depends on which capacitor he had to replace. Technically, there are three permanent split capacitor, motors in your HVAC system. Two are on the outside unit, and one is on the indoor unit.  You would have to look at your receipt from last time and see if the capacitor he replace was on the indoor blower fan motor, or the outdoor condenser unit. A short on the low side simply means that the thermostat cable running between the indoor and outdoor unit or possibly between the indoor and thermostat was shorting to ground. Depending on where the short is, it may or may not be related to your current problem.

are you located in the same town as your tenant?

AC Cooling Wizard

 

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Tkeirnan
Community Member

Hello, thanks for reply. I’m looking at invoice and the only additional information I see says, “check found shortage on low site. Found short contact. Replace it check Freon level check Compressor check capacitor all working good at this time.” In the itemized list, it says, “low-voltage wires a pair” and then its price $375. 

Yes, I’m in the same town as tenant. I was there last time he fixed it. I recall he needed access to both inside and outside systems. 

CoolingWizard
Platinum Product Expert
Platinum Product Expert

The possibility is the “short contact” might be the compressor contactor.  The symptoms would be the outdoor unit would not turn on, the thermostat would report no power.  The low voltage controls a coil in the contactor that magnetically pulls the contactor down to connect hi voltage input to the compressor and condenser fan. When this coil goes bad, it can cause a short. The low voltage side of the system is typically protected by an ATC type of fuse.  The fuse is on the inside unit. The constactor is in the outside unit. The price you were charged to fix a short sounds like the contactor.  You current problem seems to in the inside unit.  The blower motor is not starting. This could be a capacitor or it might be the motor itself.  Now, if you are mechanical in nature, together we can figure this out. 

AC Cooling Wizard 

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Tkeirnan
Community Member

Hello, thank you for your reply. I am mechanical in nature, but I don't possess a device to test for electric currents between two points. Would we need one to determine the issue? I should be able to replace a fuse or capacitor. The HVAC system is only 6 years old, so I don't think a motor would fail, but maybe. Thank you. 

CoolingWizard
Platinum Product Expert
Platinum Product Expert

@Tkeirnan ,

here’s how you could tell if it’s a Capacitor versus a motor. First get your self a metal paper clip. Turn the power off going to your air handler.  Remove the nest display, carefully remove the R wire and the G wire.  Place bare copper of the R wire and G wire in the metal paper clip. This will allow the blower fan to activate.  Now go to the air handler,  remove the metal cover over the blower fan compartment. If you look at the cabinet, wherever the power wires and the thermostat cable goes in, that’s the area where the blower will be.

Once you have the cover off, and of course the power still off, reach in and try to spin the blower wheel. What we want to know, is if it spins freely and does not stop suddenly when you remove your hand. If it does not spin freely, or if it stops suddenly, the motor bearings are bad. On the other hand, if it spins freely and it rolls on and on and slowly stops. We can do another test for the Capacitor.

You can reach in spin the blower in the correct direction. Get it sped up as much as you safely can, then turn the power on. If the motor starts and spins the blower up to speed, It’s a capacitor that has failed. Keep in mind that the motor has a built-in thermal protection device. If the power has been on, and the system is trying to run, this motor will be overheating and won’t run at all. If the motor is cool to the touch, my steps above will work. If the motor is very hot, it will not start.  

so why do I suggest a metal paper clip? You do not want to twist the copper wires because the nest back plate needs the wires to be very straight and flat if you will. The paper clip allows you to connect the two together without twisting them.

AC Cooling Wizard

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Tkeirnan
Community Member

Hi again. Thank you for your guidance. I did the paperclip connection and the blower inside the air handler works fine. When I turned the switch on, the blower turned without a problem. I believe the problem lies with the fan in the condenser (outside unit). I put everything back the way it was and after getting the screen to turn blue, it doesn’t turn the fan outside like it should. How can I troubleshoot that? Thanks

CoolingWizard
Platinum Product Expert
Platinum Product Expert

@Tkeirnan ,

we can do similar test to the unit outdoors OK. You’re going to need a sort of a skinny screwdriver long enough to reach down inside the fins and spin the fan blade. Again, we’re looking to see if it spins freely or if it is stiff or stops suddenly.

In the same way, we can do a capacitor test. But if you’ve been trying to run the air conditioner, the condenser fan motor is going to be too hot and again it’s gonna have to sit for a while to cool off. But what you’re gonna do is go outside. Have the tenant turn the air conditioner on. You will hear the compressor turn on and the fan might not.  Hoever,  if you stick the screwdriver down and flip the fan in the proper direction it takes off spinning. it’s a capacitor problem. 

The good news is once it starts running, the system will keep on running until it gets the house cooled off again. No harm no foul. But the next time it goes to turn on the fan won’t start again.

 

AC Cooling Wizard

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Tkeirnan
Community Member

I ran out of time and the technician arrived. It ended up being the external fan capacitor. He says it overheated (and hence died) because the coils needed to be cleaned. I hosed them down from the inside and outside but the technician said it’s best to use a chemical coil cleaner. He wanted to charge me another small fortune for that so I declined. How soon should I buy the foam from home depot and do that? Thank you for your help with all this. 

CoolingWizard
Platinum Product Expert
Platinum Product Expert

The capacitor does not die because of the dirty coil. Also, there is absolutely no way the previous service could get proper refrigerant readings if the coils were dirty.  The high side (liquid) pressures would have been to high. This would put stress on the compressor but not the condenser fan motor. Yes it you would be warm, but not to warm since the high pressure switch should have turned the system off. 

The process of cleaning the coils requires a special coil cleaner. This is purchased from an HVAC distributor, mixed in a sprayer with a typical 3:1 dilution. If the condenser fan capacitor has failed, the motor will indeed overheat if the air conditioner is left on. The thing I tell my customers, if the AC is  not cooling , turn it off so as not to damage it. If you get a free moment, call me at 442 283 4692. 

AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner. If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

zoeuvre
Community Specialist
Community Specialist

Hi folks,

 

@Tkeirnan, thanks for reaching out, and I'm sorry to hear about the situation. I want to check if you managed to see the response above. Please let us know if you still have questions or concerns, as we'll be willing to assist you further. 
 

I appreciate your help, @CoolingWizard

 

Best,

Zoe 

zoeuvre
Community Specialist
Community Specialist

Hi there,

 

I want to check and see if you are still in need of any help. Please let me know, as I would be happy to assist and answer any questions you may have.

 

Thanks,

Zoe