Is this a passive baffle installed in the ductwork? If so, why?


  #1  
Old 02-13-21, 02:05 PM
N
Member
Thread Starter
Join Date: Jan 2021
Location: United States
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
Is this a passive baffle installed in the ductwork? If so, why?

What is the purpose of the device shown in the picture?

It is installed in a duct running from the supply side of my furnace directly back to the return air side, bypassing the ductwork to any of the rooms. I would call it a passive baffle, with the lever and counterweight designed for it to open only when there is insufficient airflow otherwise in the system that might otherwise cause an over limit system trip.

It is a two-zone system. The ductwork for Zone 2 has only a 12x12-inch filter, while Zone 1 has a 16x20. Is the "passive baffle" designed to allow more airflow when there is a call for heat to Zone 2 only? Is that correct? Does that make sense?

The problem with that rationale is that although the airflow would be increased the added air is already heated.

I'm hoping that you here who are more informed than I can enlighten me. Thanks.

 

Last edited by Nothing Finer; 02-13-21 at 03:19 PM.
  #2  
Old 02-13-21, 03:42 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: United States
Posts: 13,756
Received 676 Upvotes on 573 Posts
That sounds like it may have been for a humidifier. Or perhaps a makeup air intake?
 
  #3  
Old 02-13-21, 06:35 PM
N
Member
Thread Starter
Join Date: Jan 2021
Location: United States
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
There is no humidifier in the system. I'm in Charlotte; no need for a humidifier.

As for a makeup air intake, isn't that essentially what I suggested, except of "making up" with fresh air, the system is recycling air to "make up" for the capacity of the Zone 2 ducting, which is otherwise perhaps too small for the furnace?
 
  #4  
Old 02-13-21, 07:25 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 62,067
Received 3,422 Upvotes on 3,068 Posts
That's called a bypass damper. It's used in a forced air zoned system.

The bypass damper is a pressure relief valve located between the supply and return duct.
As zone dampers start closing..... the bypass damper will open and divert some of the supply air to the return.
 
  #5  
Old 02-13-21, 08:17 PM
N
Member
Thread Starter
Join Date: Jan 2021
Location: United States
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
Okay, so that makes sense.

So if it's not working effectively (i.e. not opening enough), could that explain code 33 faults occurring when only Zone 2 is operating? The system works perfectly well when only Zone 1 calls for heat, but a code 33 fault is tripped after 4-5 minutes of flame when only Zone 2 calls for heat.

If so, what might be the remedy? The system is 15 years old. I've lived here a little over a year and a half, but l don't recall even trying to heat Zone 2 only. This heating season is different. My home office is in the Zone 2 space (the lower level), and in the Covid era I'm one of the newly work-from-home millions. During the workday I wanted to heat Zone 2 but there was no need to keep Zone 1 space (the main level) as warm.

If that analysis is correct, what might be the remedy? How about moving the counterweight on the bypass damper arm up an inch or so, so that it provides less resistance and lets the bypass damper open more when only Zone 2 calls for heat, with its more restrictive duct system?
 
  #6  
Old 02-14-21, 06:22 AM
N
Member
Thread Starter
Join Date: Jan 2021
Location: United States
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
I checked the duct specs (diameter) and they are all correct per the Carrier product data reference, and the ducts for Zone 1 and Zone 2 are the same diameter. I next wondered if it might be possible to retrofit a larger return air filter, so I tried running the system with no filter to eliminate the possibility that the smaller filter was the problem restricting the airflow, but no luck. Code 33 triggers again after 4-5 minutes of flame. BTW, the furnace is a Carrier 58STA070-10112.
 

Last edited by Nothing Finer; 02-14-21 at 07:41 AM.
  #7  
Old 02-14-21, 08:54 AM
B
Member
Join Date: Oct 2015
Location: Ct.,USA
Posts: 2,664
Received 235 Upvotes on 208 Posts
Any way to make the control turn off blower motor before closing the zone valve. This would eliminate any over pressure in the ducts.
 
  #8  
Old 02-14-21, 10:00 AM
N
Member
Thread Starter
Join Date: Jan 2021
Location: United States
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
Never mind, for now. I found info online about adjusting the bypass damper counterweight. I will follow that instruction. But the first thing I noticed after reviewing the online info is that the bypass damper is not level, as specified for a horizontal duct installation. I will first correct that before adjusting anything else (i.e. the counterweight). It's also cockeyed radially, i.e. the damper assembly is not installed correctly on either the X or Y axis.
 
  #9  
Old 02-14-21, 11:49 AM
N
Member
Thread Starter
Join Date: Jan 2021
Location: United States
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
UPDATE -- Still no luck. Here's what I've done.

I first leveled the duct with the passive damper in it. The pic in my first post in this thread shows the duct angling downward from right to left. I corrected that to make the duct and the damper level. With that done, Zone 1 ran longer than before the system shut down with code 33 (7+ minutes), but it didn't remedy the problem fully.

As a test, I next tied the passive damper fully open, then called for heat in Zone 2. Again, the system shut down after heating for 7+ minutes and shut down with code 33.

At this point I'm again stumped.

I appreciate that tying the passive damper fully open may not be a fully valid test, since the system is recycling heated air via the bypass. Plus, I shouldn't leave it tied open given that the system is working perfectly well for Zone 1.

I suppose the next step is to try rotating the passive damper in the duct so that its pivot shaft is also horizontal. For that I'm inclined to call in a pro, although doing it does not seem all that difficult.

I'll appreciate any informed feedback, as always. Thanks.
 
  #10  
Old 02-15-21, 06:31 AM
N
Member
Thread Starter
Join Date: Jan 2021
Location: United States
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
Thinking more about this, I think the next step is to check the Zone 2 actuator to confirm whether or not it's operating properly.

If it's not allowing the damper to open fully that could be the problem, or part of the problem. I'm skeptical that the the Zone 2 actuator and baffle are the problem because there seems to be good air flow from the Zone 2 registers when it's running, but I'm running out of possible causes.
 
  #11  
Old 02-21-21, 06:08 AM
N
Member
Thread Starter
Join Date: Jan 2021
Location: United States
Posts: 11
Upvotes: 0
Received 0 Upvotes on 0 Posts
I confirmed visually that both zone actuators are working correctly, each closing when there is a call for heat on the other zone.

I've now gotten a referral for a pro, who should be here sometime in the next few days to check things out. Here's a brief recap of the situation I typed up as a one-pager for him. Please let me know if anything I've written prompts any ideas about the cause of the problem.I live in a three-story townhome, served by two HVAC systems.

One system serves the upper, bedroom level. The other system is zoned to serve the main level, plus the smaller room on the lower level behind the garage.

The zoned system works perfectly well for the main level (Zone 1), but when there is a call for heat for Zone 2, the system runs for a few minutes, then shuts down prematurely and a code 33 is triggered.

I have looked into the fault conditions listed in the system documentation for code 33. My assessments are described below.

1. Defective blower motor or start capacitor
2. Loose blower wheel
  • I ruled out these two conditions because the system works perfectly well for Zone 1.
3. Inadequate combustion air supply
  • The unit is in a well-ventilated attic, not in a closet with restricted airflow.
4. Dirty filter or restricted duct system
  • Airflow into Zone 2 does not appear to be the problem, assessed without any professional test equipment. Airflow seems comparable to, if not better than, Zone 1 airflow from the registers.
  • I checked the air filter, and then for test purposes removed it.
  • (More on this below)
5. Defective switch or connections
6. Open flame roll-out switch, or fuse link. Manual reset or replace.
  • Thinking the fault was a false positive after considering the faults listed previously (and because the parts were relatively inexpensive), I replaced all three switches in the limit circuit (limit, flame rollout and draft safeguard switch). The code 33 fault persists.

Having initially ruled out the fault conditions listed above, I looked more carefully into the “Dirty filter or restricted duct system” condition.
  • Ducting for Zone 2 is sized the same as for Zone 1 (not surprisingly).
  • I confirmed visually that the two zone actuators are working as they should.
  • I learned about passive bypass dampers. The bypass damper opens when Zone 2 is operating.
  • I tried adjusting the bypass damper using information found online. It appears to me that the bypass damper is not installed ideally, but based on what I observed it is not restricting airflow in a way that would indicate its function as the root cause of the code 33 fault.
 

Last edited by Nothing Finer; 02-21-21 at 08:31 AM.
  #12  
Old 02-24-21, 10:17 AM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,667
Received 39 Upvotes on 37 Posts
When you say the ducts are the same size for both zones, do you mean just the main duct or main & branches?
 
 

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