I tried to move the manual switch, it would not move, but did notice that when the system was running the damper automatically opened up
I guess going back to a previous post I made, are you positive the plenums were not separated. The return looks like it’s coming from or covered by OSB. The one on the left looks like a standard supply duct, uninsulated. Just throwing it out there to ponder… 
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On a side off topic, what is the reason for drawing “outside” into a system? The reason I ask, when I had my furnace replaced in '21 it was/is a high efficiency with only the exhaust being piped to the exterior. While being installed, I told the HVAC guy that system was only able to fit to the exhaust and no additional external vent could be applied for intake.
His response was that it was no problem and probably best for the system to take internal air as opposed to external. He said the external drawn air contained more moisture than internal drawn, which would cause more problems with IAQ and within the system itself.
Interesting…
bump, might be this
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Nice link Dave, clears things up in my mind.
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You’re welcome, I’ve come across similar situations in the past and done research about this subject. There is much more information out there about this. The link I provided was the 1st link that DuckDuckGo provided… pro tip stop using Gurgle. (Note, I used to call it Glue go, a friend of mine turned me on to the term “Gurgle”.
Here in GA, I would have the same concerns. Dave’s link provided some good insight of when, where and why fresh air may be helpful. In my old leaky home, I doubt this would be beneficial.
If the outside air inlet is ducted to the return side of the central air handler, the duct should not be allowed to remain open at all times. Over-ventilation can unnecessarily increase energy use and can increase indoor humidity in humid climates. The volume and duration of fresh air intake periods should be controlled by a motorized damper that is controlled electronically to automatically provide intermittent fresh air. The damper can be controlled with a timer that is set by the HVAC installer to meet desired or code-mandated ventilation requirements
The timer can be used to coordinate periods of fresh air intake with operation of an exhaust fan operating within the home to provide balanced ventilation, so that the home does not become overpressurized.
I’ve been on a couple of apartment/condo inspections and observed widespread mold on ceilings and walls. I suspected HVAC problems to include lack of fresh air. The only ventilation were bathroom vents. One such unit had a vapor barrier atop the ceiling insulation which is very unusual in GA which may have contributed. I can see the value in adding fresh air under controlled conditions.
Morning, Neil.
Hope this post finds you well.
Questions.
Simple list what components are attached to the HVAC. AHU, Heat Pump, ERV-HRV, Humidifier, Electronic zone controller?
This an air tight home?
Honeywell vent actuators control zones.
Just a guess but the HVAC system is set up for summer winter settings.
Need more information…
Dave shared this link to answer the question i had.
Outdoor Air Intake Damper Controlled | Building America Solution Center (pnnl.gov)
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I would not be surprised if the return plenum is just an OSB box, due to the tight quarters. It would be interesting to remove the air filter to take a look see… Hopefully, it is lined and/or air-sealed nicely. I have no idea if that would be code compliant, but think it would be functional.
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