AC unit not cooling house, possibly undersized


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Old 06-18-07, 05:32 PM
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AC unit not cooling house, possibly undersized

Hi

Currently the AC unit for the house doesn't work very well. I have recently installed a new digital thermostat for it to regulate the temperatures when no one is at home. I'm sure all the wiring is correct as I got it check, there is cool air coming from the system when it is turned on.

I have set it for 29C until 3:00pm and from 3:00pm to 11:00pm, I have set it for 26C. When I got home at 4:30pm today the thermostat displayed the temperature as 28C. I let it run for 2 hours and the number didn't move, I ended up opening all the windows and it went down to 27 in about 15 mins. I'm not really sure what to make of it.

The system was never very good at cooling though my father doesn't agree, he believes it is because I set the thermostat at too high a temperature and the AC unit is running to maintain the temperature it is at but that makes no sense to me, it should be cooling the house down to at least 26 if not a couple degrees lower and then stopping until the temperature goes back up to 29 (3 degree spread from 26) and then starting up again.

I'm not really sure how to test if the unit is undersized or just breaking down due to age, I'm guessing it's at least 10-15 years old, the house is probably 25-30. It's not in the best of shape since my parents are not the most inclined to fix up small problems like sealing doors and windows. I am just trying to save them some money so they can retire in a better position but they don't seem to care.

Anyway, I'd like to know what I should do from here. Should I check if the unit is breaking down? Or try sealing up all the windows and doors (they are decently sealed just not ideal)? I'm an engineering student but I'm new to home improvement stuff. I've gone through the Mr. Electricity website and I'm trying to implement the things that would help the most

Thanks
 
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Old 06-18-07, 05:49 PM
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First of all, A/C systems respond much more slowly than do heating systems. Temperature setback on A/C systems is generally a losing proposition. Decreasing humidity is often just as important (sometimes more important) than cooling the air and humidity reduction ONLY occurs when the A/C is operating.

Sealing the envelope by increasing insulation and improving weatherstripping will always be more cost effective than spending money on the A/C system.

Make sure that the air filter is clean, the cooling coil (inside unit) is clean and the blower wheel is clean. Next make sure the coils on the outside unit are clean as well. That is about the limit an unlicensed person can do.

Set the thermostat to the desired temperature and leave it, it may take several days to cool all of the contents of the house. If after all the above and waiting a few days it still seems to be underperforming it is time to call a tech for a check oout.
 
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Old 06-18-07, 08:08 PM
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Ok, I'll do the suggested and run it for a week and see how it goes.

Thanks
 
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Old 06-19-07, 04:27 AM
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You said "I'm sure all the wiring is correct as I got it check" after you installed a new thermostat but it is possible you wired it wrong and the heat is on at the samer time as cool.
If a gas furnace this would be easy to see but if electric the only way is with a test meter.

To get a rough idea how it's cooling you could feel the larger pipe coming out of the furnace to see if it is cold and possibly sweating.
Make sure you feel under the insulation when checking.

Also, as furd has said set back on a/c will not realize much in savings and you would do well to not use that function.
 
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Old 06-19-07, 04:43 AM
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also agreeing w/ furd, a smart move (meaning min. cost and saving in the long run) resealing the windows, doors, and attic would be the first thing i would try.

not to mention a house around fifteen years is due for a new good sealing, in my opinion.

if it doesn't make sense for why you should take the time to reseal everything it's because when a house isn't sealed correctly or over time when the original seals wear down, cool air ( or even heat) leaks out, causing the unit to take longer to cool/heat the house,
also causing the unit to work much harder, therefore reducing the life of the unit itself.
anyways that's what i would do first.

-trent
 
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Old 06-19-07, 12:53 PM
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Thanks for all the suggestions. Correct me if I'm not understanding this correctly but the lower temperature during the day isn't better than leaving the AC on all the time?

I'm currently learning how to properly seal windows and doors. The windows in my bedroom look sealed to me but below the window frame the paint is chipping, and I'm not really sure what that means. The paint around the room is fine other than that. How much should I expect to spend sealing the windows and doors of the house? (7 avg size windows upstairs, 1 large metal front door and 1 wooden side door, 1 glass door in the back and 3 windows on the main floor and finally 3 small windows in the basement)

Quick question though it's an entirely different subject. The back glass door (the sliding ones) one of the panes are foggy, I think it means there is a crack however small and water moisture is getting stuck inside, is this correct?

Thanks again for the help
 
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Old 06-19-07, 03:14 PM
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hozer,

I was confused at first but your terminology is a bit off.
When you say you would turn the a/c up you must mean to a colder or lower setting which is to turn the airconditioning down.

In your original post you asked: "Should I check if the unit is breaking down? Or try sealing up all the windows and doors".

Tight windows and doors are very important for long term economy and energy savings but unless there are major gaps that would say blow out a candle in a moderate wind you may be focussing on the wrong thing.
It is entirely possible you have a service problem.

As said, a set back thermostat will not offer much in the way of savings, especially if the a/c is undersized.
As said, a/c does not only lower temperature it removes humidity which it can't do if it ain't running.

I would suggest you forget about sealing anything for now and concentrate on checking out the unit.

If you want to do this yourself we can likely help or it could also be a good investment to call in a tradesman to do this for you .

The moisture between the panes of the dual pane unit mean the seal has broken and the assembly is not providing the same insulating value.
 
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Old 06-19-07, 03:36 PM
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GregH,

Thanks for replying.

Sorry about the confusing terminology, when I say 'turn up the a/c', in my mind I'm stating 'increasing the temperature on the thermostat' (ex: 26C -> 29C) which is obviously incorrect and I made a mistake.

I don't think I have any leaks that big (except maybe one by the side door). If it is a service problem, I would like to do (and learn) as much as possible myself. I guess I'll need to get the basic information about the house and a/c system.

I'm guessing the sliding glass door will need to be replaced if it's not insulated properly, I'll make a new thread about that after I do some research.
 
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Old 06-19-07, 04:06 PM
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Couldn't edit the last message.

Is there anything wrong with closing all the air ducts on the main floor to 'force' cool air up to the second floor of the house (2 floors and a basement)? I personally think it will damage the system over time but my dad seems to think otherwise. I currently reset the thermostat so that it runs 22C at all times.
 
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Old 06-19-07, 07:09 PM
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Closing all the main floor vents will restrict airflow, reduce cooling capacity, and possibly damage the unit. Most systems do not have adequate airflow when everything is open.

If you must, close two vents MAX.
 
 

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