First summer in this 2 story house and looks like air flow on the second floor is significantly weaker then on the bottom floor. Looked at the HVAC to find the dampener handle and found 1 but it is screwed in place. Not sure if this is the duct going to the second floor or first.... Is it done to prevent the dampener from being manipulated for some reasons or its ok to just unscrew it and play with the level of open/close?
Welcome to the wide, wide world of second story air conditioning. If this was done to prevent it from being manipulated they wouldn't have installed it. This was done just to prevent the damper from closing due to air flow. Find out where this duct feeds and if it's to the first floor try closing it a bit to divert more air to the second floor. If this does feed the second floor, you might want to add a duct fan to increase the air flow. They can be controlled manually by a switch or hooked up to your air handler. Good luck.
When I set up a 2 story I usually install 2 dampers 1 for upstairs and 1 for down. I lock them in place with the flow balanced but I usually set up a summer / winter positions. In the summer I set ~60% to the upper floor and 40% downstairs. For winter I set 60% down and 40% upstairs. You don’t want to make a change much larger than that or you could split your ductwork inside a wall or have it blow off a register if flex duct. I have seen both and repairing a split trunk can be a pain in the back side especially if it is inside a wall. When I set the flows I use a anemometer and measure the flow. I mark each damper with 60 & 40 positions they should not need adjusting outside of this range and it is normal to shoot a screw in the handle if there is not a lock (many times a butterfly nut or wing nut) so you should have 2 dampers for best results if not you may have limited ability to adjust the balance and will need to open or close the individual registers in each room to get the same affect.
