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Old 07-11-2012, 07:22 PM   #1
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AC not cool enough to cool condo


My AC unit can barely keep up with the high temps and runs 24x7. Yesterday I replaced the blower motor as it died. Unit is probably 10 years old.

I replaced the 1/3HP 9.7Amp 4 stage motor with a 3 stage 1/3HP 4.6Amp motor. It was wired up only to use 2 stages, but seems only to run on high, whats the low stage for? Also how can I tell if I'm programed to use both stages, if theres a point.

Main problem we're having is our upstairs is very hot. Our new motor is 1075rpm vs 1050rpm but isn't really noticeable. Anything I can do to increase cooling upstairs or overall?

Messing around with vents it seems if I close all except one it doesn't blow out much stronger than if I have all open. I'm wondering if buying cheap PC fans to put in upstairs vents would be a good idea to promote flow.

Basement was recently finished, but only has 1 vent. I'm wondering if I possible need a larger unit. Since this is a 3 story condo and is pretty small I didn't think I'd have these kinds of issues.

Do you think main issue is low airflow or low cooling ability? Air seems pretty cold and decently strong. we have about 7-8 total vents in home and 2-3 return vents

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Old 07-11-2012, 08:38 PM   #2
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AC not cool enough to cool condo


prolly undersized unit and old incorrect duct sizing, very hard to ge cold air upstairs in old systems. Today standards they normally use 2 ac units one up stairs and one for the main floor. The low speed is for heat mode of the air handler usually.

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Old 07-11-2012, 10:37 PM   #3
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AC not cool enough to cool condo


Some units run at one speed for cool and at a different speed for heat. And those little fans won't do much. There are duct booster fans available that will be more efficient. Take a temperature reading at the supply and return air ducts...there should be a 15 to 20 deg. difference. Does the air flow start out normal and then diminish? If so look for a frozen coil in the unit.
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Old 07-12-2012, 04:51 AM   #4
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AC not cool enough to cool condo


At 9.7 amps, your old motor was more then 1/3HP. More like 1 HP.
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Old 07-12-2012, 08:05 AM   #5
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AC not cool enough to cool condo


Providing your new motor is the right size here's my suggestion. Cold air is more dense than warm air so your blower fan should run continuously on low or next to low speed and then kick onto high speed when the thermostat calls for cooling. Without using this mode of operation it will be cold on the lower level, erratic on the middle level and too hot on the upper level of your home. You may need an AC Tech to come in and wire the controls to do this. Depending on how old you may need a relay/electronic board to accomplish this. If you want to test this theory just leave the fan on continuously for a day or two to see if conditions improve. If there is not a manual switch to leave the fan on then just direct wire the blower motor on highest speed and leave it running for at least 8 hours. If that works proceed with steps above. Usually works.
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Old 07-12-2012, 04:57 PM   #6
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Originally Posted by beenthere View Post
At 9.7 amps, your old motor was more then 1/3HP. More like 1 HP.

it states A.O. smith 321P591 HP 1/3 rpm 1050 /4 spd v115 A 9.8 hz 60 ph1 type FE fr. GU 48


It seems like a lot of power for only 1/3HP and 1050 rpm.

maybe because it's like 10 years old and doesn't require a capacitor to run? new technology saves power? it sounds too good to be true that replacing the motor saves me around 5 amps.
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Old 07-12-2012, 05:02 PM   #7
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AC not cool enough to cool condo


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Originally Posted by techpappy View Post
Providing your new motor is the right size here's my suggestion. Cold air is more dense than warm air so your blower fan should run continuously on low or next to low speed and then kick onto high speed when the thermostat calls for cooling. Without using this mode of operation it will be cold on the lower level, erratic on the middle level and too hot on the upper level of your home. You may need an AC Tech to come in and wire the controls to do this. Depending on how old you may need a relay/electronic board to accomplish this. If you want to test this theory just leave the fan on continuously for a day or two to see if conditions improve. If there is not a manual switch to leave the fan on then just direct wire the blower motor on highest speed and leave it running for at least 8 hours. If that works proceed with steps above. Usually works.
I'm assuming I can bypass all controls and directly power the blower to run 24x7. seems easy enough.

What if I want to run it on med ( I have spare med wire from motor) 24x7 then keep the current 2 stages of high for AC and low for heat? will I need a relay so it doesn't provide power to med if its running low or high?
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Old 07-12-2012, 05:08 PM   #8
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AC not cool enough to cool condo


Quote:
Originally Posted by justinm001 View Post
it states A.O. smith 321P591 HP 1/3 rpm 1050 /4 spd v115 A 9.8 hz 60 ph1 type FE fr. GU 48


It seems like a lot of power for only 1/3HP and 1050 rpm.

maybe because it's like 10 years old and doesn't require a capacitor to run? new technology saves power? it sounds too good to be true that replacing the motor saves me around 5 amps.
9.8 amp at 115 volt. it used as much electric as a 1-1/4HP would have.
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Old 07-12-2012, 09:04 PM   #9
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AC not cool enough to cool condo


I am more of a boiler/commercial heating Tech but I believe you can run your AC on the two speeds as stated and when your thermostat switches to heating mode a separate circuit is used to bring the fan "on" once the heat exchanger is up to the desired heat, i.e., you only require the relay/electronic board when in cooling mode. But, just run the fan on continuous high speed for now, to see if this helps the problem. If not then unit may need servicing or may not have enough capacity.

Please let us know how it works.
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Old 07-13-2012, 06:37 AM   #10
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AC not cool enough to cool condo


cool/auto the fan cycles with the cooling cool/on the fan runs 24/7 even when the cooling is satisfied....how is the sun into the condo hitting walls and floors as it swings.set the blinds so it shades that off anything within it is eating up the cooling adding a false load.air handler should be doing 18F supply vs return taken at the unit.do you have returns on the floors including near the stat.
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Old 07-13-2012, 09:12 AM   #11
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AC not cool enough to cool condo


So, Biggles, you mean that when the thermostat is set to "cool-auto" the fan only runs during the demand for cooling and shuts off when the thermostat is satisfied but, if in the "cool - on" mode the fan runs continuously- Could be. Depending what type of thermostat and how it is wired at the fan unit/furnace. You do make a good point though. The thermostat setting may only have to be changed to accomplish continuous fan operation as I had suggested. Would be nice to know if this improves the cooling in the condo.

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