Central air not cooling


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Old 05-09-15, 08:17 AM
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Central air not cooling

I purchased this home in Nov. of 2014, its a old house built in the 50's but everything from the floor joists and up is brand new, including the HVAC.

Entire house is 1600 sq. ft., estimating basement + first floor is 1100 sq. ft. and the 2nd floor is 500 sq. ft.

My air units are good for up to 1200 sq ft each (I have 2). One unit does basement + first floor, other unit does 2nd floor.

First floor + basement = 12 air vents
2nd floor = 5 air vents

So my issue is, the 2nd floor heats and cools like a charm. Air comes out of the vents like a jet engine. However my first floor/basement is where my family spends 90% of the time, so less air gets pushed around to each of these 12 vents. These last 4 days I just started using the air conditioner in the evenings... my thermostat (with windows open) will show it being 70-75 degrees from morning until early afternoon, and then once the sun gets over the house is when it jumps up to 80. Around 78 degrees if when I shut the windows and cut the AC on. The AC cuts on around 2pm and is set to 77 degrees, and never shuts off. Keep in mind the high temperature from each of these days is no higher then 82.

Last night I got up around 2am and to look at the thermostat, and it showed 77 degrees (AC was still running) and set to 77... 10 minutes later I look at the thermostat and it has jumped up to 78! Keep in mind by this time the temperature outside was in the 60's.

Im a first time home buyer and no very little about home maintenance... but I know from living in an apartment the last 10 years I had to call the maintenance guys out to add more freon about once a year to my AC. I'm seeing online that you should be able to go to the outdoor unit and touch the larger copper pipe and feel it "sweating"/condensating from the pipe being cold in the hot temperatures of the sun. My pipes feel a little moist but I wouldn't consider it enough to actually drip off of the pipes.

When new air units are put in do they normally top it off with freon or is that something that is expected of the home owner to add after installation?

I'm not quite sure what else to do... what I was thinking about trying to BLOCK air flow in the ducts to rooms I don't need AC in... I'm never down in the basement and have a dehumidifier on about 80% of the time so that's one I can close, the downstairs bedroom and living room both have ceiling fans which I don't really need the AC in. I'm talking about more then just covering the vent, more along the lines of pinching the air duct arm that flows to these vents in the rooms the air flow is not a necessity in.

Any recommendations for me? Thank you.
 
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Old 05-09-15, 09:36 AM
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Welcome to the forums.

A regular novel here.

How was the heat delivery of the downstairs unit ?
Does it feel like the same amount of airflow out of the registers now as when heating ?
When the unit is in A/C mode is the outside unit running..... is the fan on top running ?
 
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Old 05-09-15, 09:46 AM
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Hi Pete, thanks for your reply!

Q: How was the heat delivery of the downstairs unit ?
A: The heat was about the same... weak airflow however the temperature of the heat felt good coming out of the vent.

Q.: Does it feel like the same amount of airflow out of the registers now as when heating ?
A.: The same airflow from what I can tell. It does make sense that the air flow would be dramatically lower being distributed into 10+ vents downstairs opposed to just 5 upstairs. I just wished they could've put a couple of the ducts and attached them onto the unit that controls the upstairs to make it more even.


Q.: When the unit is in A/C mode is the outside unit running..... is the fan on top running ?
A.: Yes, the fan runs on both units when cut on.


I should also add that downstairs I do have alot of windows without any treatments (curtains, drapes, shutters, blinds ect.) I have seven 2,5ft windows and two 7ft. long windows. One of the 7 footers and one 2.5 footer is near the thermostat so that's probably a cause as well.
 
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Old 05-09-15, 09:55 AM
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Have you checked/replaced the air filter(s) ?

When you feel the larger copper line outside at the condensor unit..... it should be very cold when the unit is running. If not then you may need to have the refrigerant level checked. You should not need to add refrigerant every year.

Windows near the thermostat will artificially heat the area and cause the thermostat to read warmer air but the rest of the house should still be getting cold.
 
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Old 05-09-15, 10:54 AM
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Central air not cooling

Whether the large suction line sweats a lot depends a lot on the outdoor dew point.

Many valid performance tests have shown that air conditioning systems 'on the average' only deliver to the conditioned areas between 59 & 63% of their Nominal Rated Performance.

Easy Safe testing of your A/C or heat pump cooling performance for all the visitors to use:

First, make sure the return air filter is clean, and then you should get a digital probe thermometer that reads in tenths degrees, (though U can use any mercury thermometer) and a low cost percent relative 'humidity gauge' to check the 'indoor' humidity level.

If you have an air conditioner that was manufactured between 1992 and 2005 it will 'probably be' a 10 or 12 SEER (though some were higher SEER even back then) R-22 refrigerant units.

When the temperature reaches around + 80 to 95F outdoors and the indoor temperature is 80F and the relative humidity indoors' is right around 50% RH the outdoor condenser temperature split should be around 20 to 21F above the outdoor temperature.

If the indoor temperature is 75 and the relative humidity is 50% then the air discharge temp-split off the condenser should be around 17F.

The indoor temperature split between the return-air at the supply air grille closest to the air handler should be a 19 to 21F temperature drop with either an 80F or 75F indoor temperature. This is also the indoor split with the higher SEER units at 13 SEER or above.

If the indoor temperature split is too high may have very low airflow which needs to be brought up to its normal CFM Rate.

If the outdoor condenser split is too high your air handler may be drawing hot air into the return from the attic causing the high condenser discharge air temperature; or it has dirty coils or lack of ambient airflow through the coils, check for cottonwood if trees are in the area.

On the new air-conditioning systems & any systems at 13 SEER or higher, the outdoor condenser split is lower than it is on the 10 to 12 SEER units; the indoor temp-split is the same.

New 13-SEER units have a condenser temp-rise 'at above conditions' of close to 17F; a 16 or 18-SEER usually around 9 or 10F need model numbers for more definitive numbers.

If the temps are within plus or minus a degree or two, that air-conditioner is performing fairly well; if not, call an HVAC service contractor and show them your test results; tell them you want it to pass their Delivered Performance Test.

If they don't know how to perform those tests call to find someone in your area hopefully that can do those tests; with modern test instruments they are not that difficult to do.
 
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Old 05-09-15, 01:49 PM
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First off, you're running your a/c incorrectly. Switch it on only when it starts to really warm up and it will never keep up. When you open windows, you let the humidity in which the a/c then has to remove. The more moisture there is in the air, the less actual cooling gets done - depending on the moisture, up to 1/3 of the capacity can be used just to dehumidify. Better turn it on and leave it for a few days

Secondly, this system should be serviced -> airflow issues, incorrect charge, etc can cut capacity. Adding refrigerant is not part of maintenance the the need to do so indicates that there's a leak which must be found and repaired.
 
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Old 05-09-15, 02:44 PM
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Central air not cooling

Actually Muggle was stating it on the low side.

At 80F dry bulb indoors & 71F wet bulb that's 64% relative humidity; a 2-Ton system at 700-CFM has a Sensible of only 51%; 49% is absorbing the latent heat of condensation.

If outdoor air is say 82F & loaded with moisture, say, +95% RH '& windows had been open' The A/C wouldn't be doing but very little sensible heat removal for a long time; therefore, the room-temp would not come down for a long time after the windows were closed.

His systems airflow is probably considerably lower than 350-CFM per/ton of cooling/heat removal which would make it less than 50% sensible heat removal.

Muggle is right-on concerning letting humid air into the home; not only that but it can take a day or two of runtime of a proper operating system to get the moisture removed sufficiently from all the materials in the home.

Excellent post, Muggle.
 
 

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