I ran across this AC supply duct blowing cold air into the return air space. This was a zoned HVAC system. There were two ducts in the space and both had dampers so I figure they are part of the zoning. I just can’t figure out why the open supply duct was blowing cold air into the return air space located directly under the air handler. Any thoughts would be appreciated.
Could be part of a bypass used to balance the pressure when the dampers are closed. Other than that, not enough info.
That may be. I’ve seen a lot of zoned systems but haven’t seen one that blew cold air out of the filter. The company that installed the system has been around since 1950 and has a good reputation. Just seems like if it’s what is done to balance a system that I would run across this more often.
It’s normally done at the plenum. Definitely atypical from what I see here.
So it’s blowing conditioned air throught the filter only to be sucked back into the return plenum?
And there’s 2 ducts, both with dampers.
I’ve never seen anything set up in this manner and to me it makes no sense. I would call it out as an improper installation and recommend corrections be made by a qualified HVAC Tech.
2 Likes
Best answer!
Are you being paid to diagnose the situation?
If you want to know the why’s, take an inperson HVAC class.
1 Like
I’ve taken an inperson HVAC class but this configuration never came up. If it was addressed in the class you took, I would greatly appreciate you sharing that with me. I ended up just deferring and recommending that it be checked out by an HVAC contractor.
That’s my point. It’s not any method that I (and others) have ever seen before. Would be nice to hear what an HVAC instructor had to say about it.
1 Like
I see it occasionally on new construction. A supply duct is connected to the metal return box as part of the bypass damper system. I’ve never seen it look this bad though.
Like Simon noted, it looks like dump dampeners on a zone system. Not a great set up, but it “works”. You have to get rid of the CFM if the stat is satisfied in one zone, but not the other(s).
1 Like
Looks like a matter of access. Sloppy and negates what a return plenum is designed to do, but if it works…
The supply air needs to go into the return plenum.
As Jeff Spencer pointed out, When a supply air duct zone shuts down, you need to relieve static pressure of the system, or you will below the duct seams out. Can also blow the A/C compressor by slugging the refrigerant.
1 Like