Central A/C coil frosted! Temp won't go down.

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Old 08-17-15, 07:03 AM
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Central A/C coil frosted! Temp won't go down.

Last evening, temperature wouldn't drop under 82 even 'tho it was set at 77. I felt the cold air from the vent but it's not blowing out very strong. I checked the air filter (16x20x4) which was last changed in April so I bought a new one this morning on the way to work so I will be changing it this evening.

Two things I noticed:

1) A/C unit's coil is frosted.
2) I found a couple of small wet spots underneath the furnace. I checked and felt all over but can't locate the leaks.

Please help.
 
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Old 08-17-15, 07:13 AM
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When you say the A/C unit's coils is frosted, do you mean the evaporator coil located above the furnace? If so, there are two things that normally cause the evaporator coil to freeze up: low airflow through the evaporator coil, and the system being low on refrigerant.

Was the air filter very dirty? If so, that could be restricting the airflow through the air handler (furnace). Also, if the filter was very dirty, it could result in the evaporator coil being dirty. It can be cleaned, however it's not an easy job and probably not worth attempting at this time.

If the evaporator coil is frozen, turn off the A/C but leave the fan set to ON rather than Auto. That will speed the defrosting of the coil. Once the evaporator coil is ice free, feel the airflow through the ducts (after replacing the air filter). If the airflow feels "normal", turn the A/C back on and see if it still freezes up. If it does, then you're likely low on refrigerant and you'll have to call an A/C tech to come out and try to find the leak and recharge the system.
 
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Old 08-17-15, 07:19 AM
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Frosted coil I'm referring to is in the A/C unit outside right near the ports where you refill the refrigerant.

When you say leave the fan set to ON, do you mean don't turn the A/C on but just let the fan run?

Unfortunately, I can't never tell how dirty the filter is on these thick ones.
 
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Old 08-17-15, 07:57 AM
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If the refrigerant lines, particularly the larger copper line, are frosted, chances are the evaporator coil inside is also frosted. What I meant was to set your thermostat to OFF (not Heat or Cool), but switch the Fan setting from Auto to ON. That will keep the outside unit off, but turn the inside fan (blower) on, which will speed up the melting of any ice on the evaporator coil. Only do this after replacing the air filter.

Regarding the air filter, what kind of filter are you using? If it's the pleated paper type, it may be restricting the airflow through the evaporator coil. Unless you or a family member have severe allergies, you might be better off using a cheap spun-glass filter such as the one shown below.

20 in. x 25 in. x 1 in. EZ Flow Heavy Duty Air Filter (Case of 12)-10255.012025 - The Home Depot
 
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Old 08-17-15, 08:12 AM
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I am using the pleated paper type. The one you're suggesting is only 1 inch thick. Filter slot in my furnace can fit up to 5". Wouldn't that be a problem?
 
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Old 08-17-15, 10:14 AM
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Yes, it would. Sorry, I missed that part of your original post.
 
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