Central Air not keeping up. Questions.

sue36July 11, 2011

We have two American Standard units which are 5 years old, the larger is for upstairs. I don't recall either having an issue keeping the house at the designated temperature before. I realize the system is not designed to handle to hottest days, but it should be able to handle the normal hot days, right?

I've noticed that if I set it at 73 when I leave the house it will be 76 downstairs when I get home at 7:00 pm. DH tells me it is running constantly. It seems like we have to turn the AC way up upstairs to get the downstairs cool. I don't think the air coming out downstairs feels that cold. I guess I could use a cooking thermometer to see if there is a difference in temp between the upstairs air and downstairs air at the register.

So, do you think the AC should be able to keep the house in the low 70s when it is 80-85 out? How often do these systems need to be charged? Pretty much the only thing we've done in 5 years was cover the units and turn them off every winter. Thanks.

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Sorry you are having trouble.

Here are some thoughts. Any manufacturer will have recommended yearly service for cleaning the coils and fans.If you have not had this done in 5 years then you may have dirty coils. Dirty coils cannot transfer heat correctly.

Filters should be changed about every month of use. They are so inexpensive and can do so much to extend the life of your system.

Charging or adding refrigerant is only required if there is a leak. That would be a more of a service issue, and not part of standard maintenance.

Unless you are in the extreme north of the country, then yes, your system should be able to maintain 72 degree indoor temp at 85 outdoor temp.

I recommend calling for service for cleaning of the systems.

Can you download the owner's manuals for your units on the manufacturer website. They may offer additional tips, such as running your vent in the kitchen when you cook, and other ideas.

    Bookmark   July 11, 2011 at 7:37PM
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The general interior design temp is 75 so low 70s is asking too much. But generally 73 is not unrealistic. Usually charge would not be needed but you might need to clean the fins or perform other maintenance. I would think that would be the first thing to do.

I generally shiver if I have the vent blowing on my feet. I doubt a cooking thermometer would be accurate in the 55 degree range but maybe.

    Bookmark   July 11, 2011 at 7:40PM
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"I doubt a cooking thermometer would be accurate in the 55 degree range but maybe."

Calibrate a fast-read thermometer. in ice water and boiling water. If it is OK at both temps, you should be sitting pretty.

    Bookmark   July 11, 2011 at 9:11PM
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Also, if you can, keep the window shades/drapes covering the windows closed to keep out the sun.... especially windows facing east or west.

    Bookmark   July 11, 2011 at 9:40PM
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We aren't in the extreme north, but we are in Maine. 85 is pretty regular here (it was over 90 today), 90 not all that unusual. We'll get 95-100+ once in awhile. Think slightly cooler than Boston.

The filters we have are supposed to be changesd every 3 months, which we do (they are actually pretty expensive, they are big box-like things, another is a thing you wash off that zaps the dust). The coils haven't been cleaned. As far as I know we don't have manuals, but I'll look them up or email American Standard for them.

The general design temp is 75!? Wow, that seems warm. It's 73 in here right now and I'm comfortable, but I am also just sitting. There is a vent at my kitchen sink and it feels cool, but not cold like my car AC. I think a friend of ours has a HVAC thermometer. I will see him next weekend and will ask to borrow it. And I'll get DH out there to clean the coils. There is a porch on the east side, but the sun does heat the house up in the afternoon from the west side. Not a curtain or shade in the house. I should add one to the slider in the kitchen.

Thanks for letting me know it's probably not a coolant leak.

    Bookmark   July 11, 2011 at 11:27PM
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Sue - by most standards Maine is the extreme north (since this is a 99% US forum). When you are talking a/c, you are in the extreme north.

In NC (I'll call that middle of the country since there are much much hotter places - we haven't broke 95 yet), I set our a/c at 76. At that temp, my wife can't handle the ceiling fan on if she is sitting down (ie too cold). Humidity makes a big difference and I bet your RH is high since you have such a low heating load - that will make it feel warmer. The other issue is that there really is a long term adjustment to temperature and your body is used to the frigid north.

If you have significant west facing windows without shade, that will make a huge difference. Presumably the windows are designed for the North and will allow a high gain into the house. A shade tree can help a lot. Interior blinds helps some but they still allow the heat into the house so shading from the outside is better. If you had shade trees and they were removed or pruned, that would make things a lot hotter inside.

I am still laughing over the "not extreme north" comment. Everything is relative.

    Bookmark   July 12, 2011 at 5:44AM
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There are also coils inside. you may need to make a service call to have them cleaned properly.

And yes, David is correct. Maine would not have a cooling load designed for 95 degrees. In the midwest that is the design temp, or even 105 for commercial equipment on a roof. But our friends in Minnesota have a home that is 1/3 larger than mine, and their AC unit is about half the size of ours.

Frankly, I recommend that you have a service tech out for the "yearly cleaning" of your system.

    Bookmark   July 12, 2011 at 7:59AM
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the need to add refrigerant normally indicates a leak that must be repaired or it will reoccur after a gas n go service call.

you should be getting a 60 degree supply temp minimum and a TD of 15-20 degrees.

You need a service call for systems to be checked, including coils and ductwork.

post back and let us know what service tech finds.


    Bookmark   July 12, 2011 at 8:57AM
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Indoor temps are also relative to location. I find it amusing when people complain that their air conditioning is unable to maintain 72F or 68F indoors. Lordy, my indoor temp is set at 79F at the moment, with 92F outside at 9:30 AM. My last electric bill was $237. I'd be in serious trouble trying to keep 68F inside just from the cost, whether or not the system could do it.

    Bookmark   July 12, 2011 at 10:33AM
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Comfort temperature are also affect by the relative humidity.

Typical residential systems are not designed for humidity control, but the design does take it into account in sizing the system.

One of the problems with typical residential is that it is sized for a specif maximum demand, and art any other load is oversize.

this leads to short cycling and less effectiveness in removing humidity.
There are some newer systems with multiple capacities, but it takes more than just a variable speed air handler.

It takes a variable speed compressor or a major change to the design to have a refrigerant reservoir and additional controls on the system.

Some large commercial systems operate this way, but they are far more expensive (and require more maintenance) than a typical residential system.

    Bookmark   July 12, 2011 at 10:51AM
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