Well here’s a new issue...

[grizzlebar]

New construction house about 7 months old, installed 2 Nest thermostats on a 2 zone system (one compressor and one handler). No issues until now (at least that I’ve noticed)

So I was downstairs and walked through the main hallway which I thought was quite warm - looks like there is warm air coming out of my return intake.

Made my way upstairs to check the other one, which is drawing air in just fine and pushing it out to all the upstairs vents.

Thinking i was crazy, came back down and verified - no air is coming out of the supply vents, but it is coming out of the return intake...


Thoughts?

 

[Done That]

Does the system have zone dampers in the ductwork?
All I can think is a mostly/completely blocked supply so air is "backflowing"...but i'd think it would trip a limit super fast??? Weird....

 

[grizzlebar]

So I’m pretty the supply/return main lines got mixed up when everything was put together. Only thing I can think of that explains full outflow at the return vent.

I guess I never noticed it before...

 

[walta]

If only one zone is calling for heat the system may be setup to dump any excess air pressure into the return system and some air may escape a nearby register

Walta

 

[yeldogt]

Is it variable speed --- how is the system controlling the zones?

It could have a bypass if the system has no other way to balance

 

[grizzlebar]

Even turning off the upper zone it still happens. My money is on crossed lines.

 

[nsula_country]

Nest thermostats... Oh boy!

CT

 

[grizzlebar]

 

[nsula_country]

So I’m pretty the supply/return main lines got mixed up when everything was put together. Only thing I can think of that explains full outflow at the return vent.

I guess I never noticed it before...

System has been commissioned and running 7 months. Wierdness recently noticed. I'd bank on a zone damper issue before assuming supply/return ducts crossed up...

Made a joke with the Nest Tstats. They are finicky at times. Like they are self aware, which they are.

Are the Nest's controlling the system? The zoning? Have a zone controller? Need more info.

CT

 

[yeldogt]

I'm assuming it's must be a 3rd party zone system. All the recent manufacturer zone controls require manufacturer specific thermostats.

OP should take some pictures of the system and look at the zone controllers to make sure they are operating

 

[nsula_country]

Even turning off the upper zone it still happens. My money is on crossed lines.

Flex or rigid duct?

CT

 

[grizzlebar]

Flex

 

[bczygan]

Raccoon stuck in a duct?

Bill

 

[nsula_country]

I'm assuming it's must be a 3rd party zone system. All the recent manufacturer zone controls require manufacturer specific thermostats.

OP should take some pictures of the system and look at the zone controllers to make sure they are operating

This is why I made the Nest statement earlier... Universal tstats and zoning don't always play nice.

CT

 

[grizzlebar]

AC guy came out - supply and return lines were crossed during installation

 

[nsula_country]

AC guy came out - supply and return lines were crossed during installation

Oh wow... How did they F that up?

Glad it was discovered. Is the AC guy that found it the same contractor that errored?

CT

 

[shadycrew31]

This was a fun thread to read, thanks for the entertainment. Glad you got a solution.

 

[LS6 Tommy]

So I’m pretty the supply/return main lines got mixed up when everything was put together. Only thing I can think of that explains full outflow at the return vent.

I guess I never noticed it before...

That is the only thing it can be. Changing the stat would not change airflow direction, even with malfunctioning zone dampers.

Tommy

 

[LS6 Tommy]

Well, I didn't read far enough down the thread... Again...

Tommy