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Old 03-15-2012, 04:15 PM   #1
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AC blowing cold but not cooling the room


I have a 600 sq ft single room home office with lots of windows (only on the front) and its own central air unit. The windows are double pane insulated and the doors are heavy solid wood with stained glass. There's a basement underneath and 2 floors above.

My problem is that in the summer I can not get the room below 80 degrees - even when it's cloudy (though at night it'll get down to 77). I've had the unit serviced by 3 companies who all tell me it's the correct size and blowing plenty cold. It runs nonstop, pumping cold air into the room that, for some reason, stays hot.

Last summer I spent a ton on UV window film tint that made no difference at all. I'm tempted to buy one of those portable AC units but am not convinced that it'll help.

Is there anything I'm missing or can do to get this place below 80 degrees? I'm in Maryland, so it's not like Florida or anything.

Thanks for any feedback!

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Old 03-15-2012, 04:19 PM   #2
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AC blowing cold but not cooling the room


what type of unit are you using?

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Old 03-15-2012, 05:39 PM   #3
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AC blowing cold but not cooling the room


Your radiant load is monstrous. What size unit do you have?

Also how old is it and has it been maintained?

If you keep the doors open to your office, it would make a difference.
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Old 03-15-2012, 05:56 PM   #4
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AC blowing cold but not cooling the room


As above.

What size is your A/C.
If a ducted system, whee is the duct work located.
What equipment is in this office.
What direction does the front face.
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Old 03-15-2012, 08:55 PM   #5
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AC blowing cold but not cooling the room


Thanks for the replies!

The front (with all the windows) faces Southwest. The late afternoon sun comes in pretty hard.

The ceilings are 12' tray ceilings with ceiling fans (2).

The unit is 1.5 tons (I think, I'll check outside tomorrow) and the ductwork runs through the basement.

The system is about 5 years old and I have it maintained about once a year. The company comes out, cleans the coils outside, checks the fluid levels and puts a thermometer in the vent. Everything usually checks out. Not sure what kind it is but it's the kind with a unit outside that feeds to a blower located in the basement that blows through 5 vents in the floor.

The equipment is a couple of computers on desks and a flat screen.
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Old 03-15-2012, 09:38 PM   #6
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AC blowing cold but not cooling the room


Return air in the room? You did say that this system is particular to the this one office alone, right? What size ducts are feeding it (are there any going off to any other rooms?) and do you have ample return air? Also, lift could be a factor meaning from the basement to the third floor is how high? I believe that systems are designed for no more than 25' of lift meaning how high the compressor can push the refrigerant without losing capacity. Then factor in the bends of the line set; each 90 degree bend equates to 3' of presure drop and so on and so forth...

Piston or txv metering?

Just thinking aloud..
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Old 03-16-2012, 03:31 AM   #7
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AC blowing cold but not cooling the room


5 supplies. Hope they are 7" if its flex duct.

How many computers. 2, 3, 5?
How many people, 2,3, 5?
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Old 03-16-2012, 07:49 AM   #8
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AC blowing cold but not cooling the room


if you can do setpoint at night the interior load is too much with the lights off.like mentioned need a tru return from the conditioed space need to get as many air cycles as possible to drop the temp. check air handler with thermometer 18F give or take on a fully charged unit running with a load...does the sun bang the condenser at anytime during the day...if any sun is hitting the sills or walls that will eat up the cooling BTUs...did it ever get super cold within as stuff was added PC and towers
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Old 03-16-2012, 03:23 PM   #9
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AC blowing cold but not cooling the room


At night the unit gets the room down to about 77 - but that's it, and it'll run nonstop.

Air flow/temp: The last time I had it serviced the tech measured the air and said something about a 20 degree difference and that the unit was blowing plenty cold. You can put your hand over the duct and feel the air blowing really cold and strong. In fact, you can feel the air from each vent reach about 8 feet into the air (though barely).

Lift: the unit is tucked away behind the house in the shade and everything runs level to the room, which is also on the first floor. And yes, this is the only room the unit cools.

Duct work: the ducts in the basement are 10"X12" rectangular metal that steps down right before it meets up with each vent.

Return: the room has two 16" return ducts -- one near the floor and one about 7' above it. They both feed into the same duct that returns to the unit.

Computers: my main computer does pump out some heat. However, as an experiment last summer I tried leaving everything off for a day and found there was no difference.
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Old 03-16-2012, 04:26 PM   #10
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AC blowing cold but not cooling the room


Quote:
Originally Posted by DanStone View Post
At night the unit gets the room down to about 77 - but that's it, and it'll run nonstop.

Air flow/temp: The last time I had it serviced the tech measured the air and said something about a 20 degree difference and that the unit was blowing plenty cold. You can put your hand over the duct and feel the air blowing really cold and strong. In fact, you can feel the air from each vent reach about 8 feet into the air (though barely).

While maybe not all of the problem, you have low air flow.

Lift: the unit is tucked away behind the house in the shade and everything runs level to the room, which is also on the first floor. And yes, this is the only room the unit cools.

Duct work: the ducts in the basement are 10"X12" rectangular metal that steps down right before it meets up with each vent.

What size duct feeds the supply registers.

Return: the room has two 16" return ducts -- one near the floor and one about 7' above it. They both feed into the same duct that returns to the unit.

This 16" duct. Is it the the register on the wall that your talking about? Sounds like its just pulling its return air through the wall cavity, which isn't big enough.

Computers: my main computer does pump out some heat. However, as an experiment last summer I tried leaving everything off for a day and found there was no difference.
Did you check your ducts in the basement for leakage.
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Old 03-16-2012, 06:09 PM   #11
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AC blowing cold but not cooling the room


600 sqft space and a 1.5 ton unit, it should be freezing, that your room should be like a meat locker. I have a 2 ton, that cools a 820 sq ft main living space, same for our basement, and it can get cold enough at 72, you have to put on a jacket.

Something is wrong here, if yours cannot keep up.
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Old 03-17-2012, 09:25 AM   #12
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AC blowing cold but not cooling the room


yeah, the radiant load plus what Been asked.

How about the filter?

Last edited by hvac5646; 03-17-2012 at 09:33 AM.
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Old 03-17-2012, 11:07 AM   #13
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AC blowing cold but not cooling the room


I'm learning a ton, here - thanks again, guys.

Return duct: It is the registers that are 16" square. The duct behind it is like 15"X12" or so. Both registers feed into the same duct.

Filter: I replace it religiously at least every 5 years. Kidding - once a month in the summer.

I'd love to hear more about the radiant load. What is that and how do you figure it?

Gregzoll: that's the same thing 3 HVAC techs have told me - which is why I'm scratching my head. They keep saying the unit is functioning well and should be able to cool the room. They have to be missing something. Maybe my high ceilings? Maybe all the windows? Terrible insulation? The fact that I'm downtown right on the street downtown surrounded by concrete? Poor insulation?

I can tell you that in the winter the same unit heats the place up from 60 to 80 in less than 3 minutes.
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Old 03-17-2012, 11:17 AM   #14
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AC blowing cold but not cooling the room


Does that return duct behind the register run directly to the Air Handler.

What size is the supply duct to the supply registers?

Being near the concrete does have a big effect.
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Old 03-17-2012, 11:42 AM   #15
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AC blowing cold but not cooling the room


Find someone in your area that can use a FLIR camera to check for cold zones, or uninsulated areas of the wall. Overall, how large is the home all together, and how many units in the home to help cool it? You can also do like I did, and get a weather forecaster from Radioshack, that uses remote sensors and place the three other sensors in various places in the room, or house, and get a overall temp of what the house is doing with cooling and heating.

It may come down to getting a environmental company that can check everything by using sensors placed in the room, and ductwork to find out if it is performing best. Going back to the equipment, post the model # and manufacturer # of the outside units, inside units, and any axillary equipment also attached to the hvac system. You can also get a cheap airflow and temp sensor either at Lowe's, Home Depot, or order online at amazon.com, which can give everyone an idea of your cfm and temp at various registers.

Now of course, if the cold air return is not doing its job, that can cause the room to stay warm or cold and the system would draw from elsewhere.

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