I just had to replace the blower motor in my home unit.

I never felt like it had enough flow out of the vents but I went back with the same rated RPM motor anyway.

The ducts are clear and the evaporator is clean and not freezing over.

My question is this, if I put in a faster fan motor, will it help with cooling or are they pretty much sized to the unit in such a way that a faster fan will cause the air to flow too fast to "chill" properly?

Usually it's the size of furnace and then the ductwork is sized and balanced accordingly. Motor size and rpm is pretty consistent based on the size of the furnace so maybe you can change pulleys to get more out of it, or do they use different blowers? I think I'm just add more confusion to this

Bunch of question, where area do you live in, has the evaporator ever been cleaned, what is the model of the furnace, the square footage of the house, the model of the evaporator and the condensing unit? Are your registers in the ceiling or the floor? Is it direct drive or belt drive?

Probably the fan is direct on the motor shaft and in order to move more air will require more horsepower, which will require an upgrade in electrical components to carry more amperage. Most of the systems I have encountered have low register velocities. You may want to balance the air flows per room. You may be dumping a majority of your air at the closest register to the air handler, which might need to be restricted to push the remaining air further downstream.
Another option may be to add an auxiliary duct fan in the duct work but that would not be my recommendation, this would lead to a higher velocity across the filter (with any fan capacity increase) which is not desirable.

I am not a pro but have learned that in most combination gas furnace/ air conditioners the air flow is sized to keep the heated air way down at a very safe level so that a child would not get the mildest burn from touching a register. This faster air flow is then not “ideal” during air conditioning season to remove as much humidity from the house air. Comfortable summer air inside the house is not just low temperature, low humidity is a big part of comfort. If you blow too much air through the evaporator the air does not get close enough to the “dew point” to maximize de-humidization. This is why many units have a relay that switches the blower motor to a lower rpm when the AC is running. This is also why you need to make sure the drain lines stay unclogged from mold.

The shutters on all the registers at the ends of the ducts of a 2 story or very spread out house ideally would be adjusted when switching from heating season to cooling season.
You cannot avoid the “hot air rises and cool air sinks” differences.

Two story houses create such differences that a separate AC for each floor makes sense even at added cost ( plus if one AC fails you sleep in the other cooled zone temporarily).

Buying a little hand held wind gauge like the “Kestrel” or its cheap knockoffs can be very useful to adjust registers, and it is not a bad idea to make “air measuring hood” out of a cardboard box to channel the air so that the wind gauge has an even flow to measure, instead of having to guess how to sweep the guage continuously over different sized openings.

It is very common for the return air ducts to the suction side of the air blower to be too small. A “choked” situation at the suction dramatically lessens air flow output of a wheel fan. It is also easy to miss that each little cross connection on the wheel is actually a tiny airplane wing that is very sensitive to dust building up on its underside. It is tedious to scrape clean the wheel wings but it can make a big difference. Most owners do not realize that is a hidden reason why there is an air filter - to protect the little wing undersides. Dust ruins the wing performance justlike ice on airplane wings can cause the plane to fall out of the sky.

Great information!! Thank you for taking the time to post that. It really doesn't take much effort to help an HVAC system. Just simple things like hosing off the condenser outside is a huge help. Cotton wood trees in MI can really screw up your AC system.

My HVAC was replaced some years ago. The new unit uses a motor controller to control fan speed, much quieter than the the old one that is for sure. The fan usually runs 24x7 at low speed to keep the house temps stable, winds up to high speed as the AC or heat comes on. Even teh compressor fan is controlled, much quieter too.

I wonder if it is setup to consider your above observations, since that is entirely possible in software? I never noticed. Did have hte air flow balanced. Used to be the front bedroom got all teh AC or heat. Turns out the old plenum was shaped to direct all that flow to that room. Had a new plenum built and my AC bills have been about 1/4 what they were with all the changes made.

Thank you for the info.

To answer some questions posed.

House is a 1200 sq foot upstairs with 1 vent in the mostly closed off basement. I live in middle TN which puts me in the area of middle of the road everything except pollen. Heat, Cold, Humidity are in the middle of the spectrum.

It is an older nordyne split unit unit with a direct drive motor on the squirrel cage. I upgraded the HP of the motor not because of performance but the original was an 1/6 HP and locally I was only able to source 1/4 and 1/3 hp's. The one I replaced it with was the same RPM but less amperage draw than OEM. Obviously new motors are more efficient.

I clean the condenser coils several times a summer to maximize efficiency and because it picks up lots of visible debris. I clean the evaporator coils at least once a year.

The comments on register flow and humidity all make a lot of sense. The one register in the basement used to feed one of two vents in the living room but when the previous owner decided to refurb the basement he opened it into the basement. I am gong to look at obscuring it at least partially and see if it helps. It is the first duct off of the main duct and it is literally 1 foot off of the main box duct. I'm sure it is probably taking to much out of the system. We don't use the basement for more than storage and laundry.

It is probably time for a new unit but I am trying to eek a few more years out of it.

I really appreciate all the advice.