Weak air flow from vents

Old 07-06-09, 03:18 PM
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Weak air flow from vents

Hello everybody,

This is my first post here. I searched but can not find any info. My girlfriend's house is about 1500 square feet, single story, near Orlando, Florida. The AC has always been very weak. It runs and runs but doesn't really cool the house efficiently. Last year she had the compressor replaced. This year the AC quit altogether. I replaced the fan start cap on the outside unit and it worked again but still had weak flow from the vents in the ceiling. I cleaned off the screen under the condenser coils in the bottom of the air handler inside the house and I got up in the attic and re-taped the ducts back to the sides of the air handler and re-taped the ducts to the metal duct works running the length of the house.

The air flow is very weak from the vents. The only vents that really put out much air are located near the air handler and the one in the kitchen, but they still do not move very much air either. The house is hot. During the day with the themostat at 68 degrees, the thermometer on the thermostat never falls below 80. It's bearable at night but not much cooler. The AC runs constantly and the power bill is way too high.

There is no ice on the pipes that I can see, and the filter is clean and changed regularly. The air handler is in a closet in the hall, a closet with the slatted doors to allow air flow. When I get under the air handler where the filter is installed there is a lot of air moving, but not much at all from the vents. I took out the blower motor and cleaned all the fins with an old toothbrush.

What can I do to improve the air flow? The ducts appear to be clean. Is there another filter in the top of the air handler that I do not know about? Or is it better to install a blower that turns faster and would move more air?

I appreciate any help you all can offer.


Old 07-06-09, 05:12 PM
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There is no filter on the supply side. A faster blower won't help either. Basically she has a poorly designed duct system [so common in FL]. The solution is to do a load profile and duct sizing.

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Old 07-06-09, 06:18 PM
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This may have been a bad ductwork design situation.

This is so very sad, the airflow problem should have been fixed as soon as any tech came near it.

Doesn't cool, but so-called tech's don't check the airflow.

Anemometers don't cost much & can ball-park CFM airflow.
Magnehelic gauges don't cost much & can be used with the blower's static pressure data showing the related CFM airflow.

The duct system has to be well sealed & the blower wheel blades clean as do the evaporator coil & fins.

There are no excuses for not detecting & rectifying inadequate airflow.

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