Air Conditioning - Weak air conditioning on second floor

I live in a two-story house with one heating/AC unit that has two zones. The AC seems to work fine when it's set to the first floor (Zone 1) and the air flow coming out of the ducts feels cold and strong. However, when set to Zone 2 (second floor) the air flow coming out of the ducts is very weak and, as a result, it takes hours to cool the second floor just a couple of degrees. For example, last night the upstairs temp was 84 and it took seven hours to bring the temp down to 78 and another four or five hours to bring it down to 74. I can feel cold air coming out of the upstairs ducts, but it's just not a strong flow of air like downstairs.


I was in the basement and the ducts felt very cold, so I don't think the issue is that the AC is not producing cold air. It's just that the cold air isn't effectively making its way to the second floor.

Admittedly, my air filter was three months over due for changing. I changed it yesterday, but that really didn't seem to fix the problem.

It's been very hot here in NJ for the last couple of days. I checked the attic vent fan and it seems to be working properly. It is set to run at 100 or 110 (not exactly sure) and was running all day yesterday. The attic was quite hot.

Any suggestions would be greatly appreciated. Thanks in advance.

Id check and make sure the main floor zone damper is working! When it is that hot on top floor zone damper should be closing at least 35% on main floor.

Airman, what exactly does that mean? Can you explain further in laymen terms. I'm somewhat mechanically inclined but heating/AC is not my strong suit. How do I go about checking the zone damper? Thanks!

You should have a damper that is in the duct that is hooked to a small motor on the outside of the duct. There should be Two, one for main floor and 2nd for 2nd floor. These should be near the air handler. Is your 2nd floor thermostat on cool?

Okay, I see exactly what you're talking about. Each duct where it originates out from the furnace has a little orange box attached to it labled "Automatic Opposed Blade Damper" with wiring coming out of each motor.

Right now, the upstairs thermostat is off, but the temp is already at 78F. Should I turn it on?

Yes turn it on and make sure the damper is open.

I fixed the problem (for the most part). The second floor damper stays in the closed position even when the AC for the second floor is turned on. I had to manually rotate the little arm on the motor to open the damper. That solves the problem of getting the cold air adequately flowing upstairs, but I don't know why the motor for that damper isn't working. I checked all the wire connections and they seem to be connected properly. Do these motors fail frequently? House is nine years old and the damper motors have the date 1999 on them.

I tested the upstairs thermostat and the temp dropped from 81 to 77 in an hour so that's good. Thanks for the help, Airman.

We only have one unit for our 2 story house and the upstairs is at least 10-12 degrees hotter or more than the lower level. Any suggestions for this?

It's the same in the winter, too, with the upstairs being considerably cooler.