Go Back  DoItYourself.com Community Forums > Heating, Cooling, Air Conditioning, Ventilation and T-Stat Controls > Thermostatic Controls
Reload this Page >

Installed Nest Thermostat and it turns on A/C compressor with the heat?!

Installed Nest Thermostat and it turns on A/C compressor with the heat?!


  #1  
Old 01-21-13, 01:37 AM
A
Member
Thread Starter
Join Date: Jan 2013
Location: United States
Posts: 2
Received 0 Votes on 0 Posts
Installed Nest Thermostat and it turns on A/C compressor with the heat?!

Hello!

Yesterday I installed my new Nest thermostat (the second generation one) and today I noticed that it is turning on my outside a/c compressor along with the heat. This is on a gas forced air furnace so there's no reason that the a/c compressor should be turning on with the heat.

It's a five wire system and I wired it up exactly as the instructions said.

C=Common (blue)
R=Rc ( I think?) and the old thermostat had a jumper to RH but the nest doesn't require the jumper
Y1 is where it gets a bit weird. It was in Y1 on the old thermostat but when I opened up the furnace the Y1 terminal wasn't connected but the yellow wire was instead going to the Y2 terminal. Is this the problem?
There's also a white and a green wire.


The entire HVAC unit is only about 3 months old. The furnace is a dual stage unit with a variable speed blower. The a/c is a single stage compressor.

I pulled the exterior fuse on the a/c compressor so that it wouldn't get damaged by running in the cold temps (it's about 35 degrees here in southern Ohio right now) and now the compressor is buzzing even though it has no power. (UH OH)

Any help would be truly appreciated!!!

Thanks!!!
 
  #2  
Old 01-21-13, 10:32 AM
G
Member
Join Date: Oct 2002
Location: Hamilton County, Ohio
Posts: 4,295
Received 2 Votes on 2 Posts
Your A/C is still receiving power - from the thermostat. It is pulling in the contactor relay in the A/C which is the source of the buzz. Something is not wired correctly at the Nest.
 
  #3  
Old 01-21-13, 04:47 PM
Houston204's Avatar
Forum Topic Moderator
Join Date: Oct 2009
Location: Texas
Posts: 7,537
Received 38 Votes on 34 Posts
The furnace is wired correctly.

Stat Y1 connects to furnace Y2 if you have a single stage cooling unit.
(Y1 would be reduced capacity cooling and Y2 would be 100% capacity. Since you only have Y1 any cooling demand is 100 % cooling capacity and requires the furnace Y2 terminal energized for the correct airflow)

It's a bit tricky to go back and reconfigure the stat after the initial install but this can be done without removing the stat from the wall and pushing in the single button for 10 seconds to reset the stat if my memory serves me correctly.

You are configured for heat pump. Change this to gas furnace with straight cooling.

Nest is an okay stat but the manual is Very disappointing.

What furnace model do you have? Do you have any unused stat wires?
 
  #4  
Old 01-21-13, 07:31 PM
A
Member
Thread Starter
Join Date: Jan 2013
Location: United States
Posts: 2
Received 0 Votes on 0 Posts
Thanks guys!

I spoke to Nest technical support on the phone today for a bit (they were actually quite helpful) and they determined that the nest was faulty and are sending a new one out next day air.

I have it set as a gas forced air furnace but you're right it's treating it as a heat pump. Hopefully the new Nest will work as it should.

Thanks again!! I'll post up after I get the new one installed. Hopefully it solves the problem. In the meantime I simply disconnected the yellow wire to remove the a/c from the circuit altogether.
 
  #5  
Old 01-21-13, 10:10 PM
hvactechfw's Avatar
Member
Join Date: Jan 2011
Posts: 6,244
Received 4 Votes on 4 Posts
I have heard of this many times with nest having sub-base issues causing this. Make sure you put a new sub-base on as well.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: