My Central A/C doesn't work when it's too hot outisde...HELP

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Old 03-11-14, 03:19 PM
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Exclamation My Central A/C doesn't work when it's too hot outisde...HELP

My Central A/C system cools my home perfectly on semi warm days. For example today the high is 77, and all day long it has been blowing freezing cold air when it's on. On days where the high is 84 again it blows freezing cold air. But on days when the high is 95, it only blows really cold air late at night but during the day it does not keep my home cool at all. It will constantly run, and the air coming out of the vents is not freezing cold or even cold like it is on semi warm days. I would call the air that comes out luke warm or just a little coolish but not cool air. This is the third year now that I have been having this problem. I would greatly appreciate some suggestions as to what is causing this. So far we haven't had a high above 80 this year and it has worked amazingly well, only has to run for a short time and blows freezing cold air out of the vents but I know once summer approaches and our humidity and temps rise, it will once again do the same thing it always does and not keep the house cool. Thank you so much for any words of advice, suggestions, and possible causes you can provide me. I really appreciate it.
 
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Old 03-11-14, 03:24 PM
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Welcome to the forums.

Did the A/C used to work ok..... in the past...... when it was that hot did it cool ok ?
The first though that comes to my mind is that your system is low on freon.
 
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Old 03-11-14, 03:27 PM
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First , check the furnace filter and replace as necessary . Next check the outdoor coold & see if it needs cleaning . Then same for the indoor A-Coil .

Is the outdoor fan running OK ? Indoor fan ?

Then have the temperatures and pressures of the condenser unit checked ( refrigerant ) . Distinct possibility it may be low on refrigerant .

God bless
Wyr
 

Last edited by Houston204; 03-11-14 at 09:03 PM. Reason: This site does not recommend homeowners handling refrigerent.
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Old 03-11-14, 08:58 PM
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Sounds like symptoms of a dirty outdoor coil or a return air duct leak or both.

Rinsing the outdoor coil should be performed annually.

A measurement of the air entering the return air grill and another measurement of the return air a few inches from the furnace on the hottest part of the day could help prove return air duct leakage.
 
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Old 03-18-14, 01:27 PM
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Could be a couple of things. As PJmax asked, did the system work before at some point when it was hot out? Most ac units are designed to operate effectively in temperatures as high as 95 deg. F. Above that, you may get a 20 deg. F difference between the outside air temp and the inside temp. If your outdoor unit is dirty, as mentioned above, it is not going to operate at peak performance. This problem will show itself more and more as the outdoor temperature increases. When was the last time you had it professionally cleaned and serviced? Also, the indoor unit is equally important. Be sure that you have ALL vents open and all return grilles clean and unobstructed. It is a myth that closing a vent in one room diverts "more" air to another. What you are doing is increasing the velocity of the air throughout the system, but reducing the volume of air. This causes problems because the system is designed to have a particular "CFM" level to perform at maximum efficiency. Reducing the airflow causes the system pressures to become unstable and you reduce performance. The indoor blower fan, coil and filter also need to be clean for peak performance. If you haven't had a professional preventative maintenance service recently, I would recommend that first. Also, my personal preference is to run the indoor fan all day rather than have it cycle on and off. The reason I do this is to prevent stagnant air in different parts of the house. By running the fan all the time, the air circulates and you get a more even distribution of cooling. The indoor fan does not use that much electricity and will not cause a noticeable increase in your utility bills. Last, if you have a mercury thermostat, make sure it is level. If you do, you should look into getting a programmable thermostat for your system. They are inexpensive and very effective. I hope this has been helpful to you. Thank you.
 
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Old 03-20-14, 05:55 PM
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Not Cooling when it gets Hot Outdoors

It is amazing how poor the service work is.

Follow the advice given concerning cleaning everything, etc.

Get a low cost ($10 or less) humidity gauge at a local hardware store.
At 50% humidity & 75F indoors, if it's a 10 or 12-SEER condenser, the outdoor condenser discharge air-temp-RISE above outdoor temp should be around 18F.
A higher indoor humidity will increase the outdoor split, due to a higher latent load.

A Return Air leak bringing hot air into the blower from the attic or a hot garage area will greatly increase the split; especially when it is hot & humid outdoors.
This could cause the change in cooling you're experiencing...

The indoor temp-split between return-air-temp & supply-air-temp should be around 19 to 21F. A higher indoor humidity will result in a lower temp-split.

Knowing the indoor relative humidity is essential to trouble shooting a system using temp-differences.
 
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Old 03-27-14, 04:39 AM
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A 12-SEER Outdoor Condenser Temp-Split

CORRECTION:

At 50% humidity & 75F indoors; 85F outdoors, if it's a 12-SEER R-22 condenser, the outdoor condenser discharge air-temp-RISE above outdoor temp should be around 17F.

A higher indoor humidity will increase the outdoor split, due to a higher latent load.

A 14-SEER R-22, same above conditions, only gets an 11F condenser temp-rise.
- Darrell
 
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