Possible cooling problem

[jlohrenz]

We just purchased a two story home with a full basement. The AC is a 2.5ton Carrier system with Puron installed in 1999(The natural gas furnace is also carrier, but I am unsure how old it is..possibly 15 yrs old). This past week we had consistant days in the 90's and noticed some problems.
First off, we could not keep the house below 78. The upstairs was consistantly above 80 degrees. I have checked the attic insulation, and for our area (Twin Cities MN) it is atiquately insulated. The ducts on the second level have hardly any airflow coming through them whatsoever.
We have tried several things. First we closed the ducts on the main level of the home. This did nothing. Then we closed the basement door as we were told all our cold air was going to the basement. (our outside unit froze up once and we had to leave it off for quite some time.)
Then we have been trying a combination of the above. The outside unit hasn't frozen up since, but we are still having problems cooling.

Even on cooler days, such as today where the temps are in the lower to mid 80's it cannot cool below 76, and the upstairs is at least 78.

We are schedule to have a tech come out later this week from the company that installed the updated AC, but was hoping to get some tips here and possibly some good questions/things to look out for when I talk to them.

Thanks in advance.

Jason

p.s. we've had some people suggest getting duct booster fans, but I have not installed them as I do not know if they would really benefit.

[docholiday]

You really need to let the tech review it, tell him your concerns. In the mean time, I wouldnt close off any registers, thats just asking for a freeze-up. Check and replace your filters. It really could be one of a bazillion different things that can reduce system capacity.

[James 3528]

Offer him cool drinks and show him where the unit is.

[jlohrenz]

Thanks.

The filter was the first thing that I replaced. Is there ever a problem matching up the furnace/air controler with an air conditioning unit?
I'm just trying to figure out why the previous owner replaced teh 15 yr old AC and not the Furnace as well.

[deejoe]

Is there adequate RETURN air in these upper rooms?
When there is no exit for return the supplly will be stalled.
Slightly close down any real cold room registers and fully open all the hard to cool ones.
For now, close off all basement supply registers.
Also, make a check to see if any of the branch "takeoff" dampers at the trunk line are fully open on these hard to cool rooms, thus not permitting proper air flow into the small run that serves these rooms.

[jlohrenz]

Yep. Every room upstairs has a return vent up towards the ceiling. I can feel them drawing air in..which I guess is a good thing. We also closed up the return in the basment.
I'm going to check the dampers today.

Is there any reason why it would freeze up if the door to the basement is open?

Unfortunately since it was so hot last week, most of the HVAC people are busy so we have about a week before we'll get service.

[dash]

Freezing when closing the basement door,indicates an imbalance in the supply and return air distribution.Hold the almost closed and see if air is flowing in or out of the basement.

[jlohrenz]

I should rephrase it. When the door is left open it will occasionaly freeze up.

When I close the door, I can feel a draft flowing under the door to the basement.

We are currently finishing the basement. There is only one return air duct, which we closed up until the basement is finished. There are no vents 'plumbed' for the basement yet, so all the cool air, and return air should be coming from the main or upper levels of the house.

[docholiday]

If, you have closed the return in the basement, there is no reason the air should be pulling under the door. likely the return is undersized and the return duct in the basement is leaking (sucking through leaks). The cold basement air, which seems to be present in the return, is lowering the load on the unit to the point it freezes.

I would reevaluate the size of the return and make sure it isnt leaking. Could be an end cap is off or panning has been pulled or something like that. None the less, basement cool air doesnt make for very good return air.

[jlohrenz]

So If I'm understanding you correctly, if the basement return is closed, then there shouldn't be any air pull to the basment. If there is there is a hole/leak in my return runs that go from the basement to the other levels.

Makes sense. So basically if the above is taken care of, the basement door being open or closed really shouldn't have any effect on the AC.