Central AC blows cool but no longer gets below 75F

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Old 06-13-15, 11:06 AM
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Question Central AC blows cool but no longer gets below 75F

12 year old house and AC, separate system for main level is working properly (blowing ~45F air), upstairs system appears to have been working properly until this week. It may have been a gradual decline but it became obvious recently that the system blower would be on for longer periods, to the point where it can no longer cool upstairs below 75 or so. Air coming out of the vents is around 65F. This system resides in my attic where the temps are above 120F even on a modest day like today (low 80s and sunny), but it worked without problems until this year.


Observations:
Systems triggers on and off properly once desired temperature on thermostat is reached.
Panel filter is new.
Fan in condenser outside kicks on when systems starts, air coming out isn't really warmer than ambient. The properly functioning system for the main level is blowing out much warmer air.
Coolant line definitely gets cold but it doesn't stay that way for long. Not as cold as the other system.

System details:
Amana 80SSE furnace with CCF24FCC evaporator (?) in attic.


Any ideas on what I can look into? Does the fact that it works marginally suggest low freon? I am moving in the next few months so am not too keen to swap out a lot of parts.


Thanks.
 
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Old 06-13-15, 11:11 AM
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Sure sounds like it's low on refrigerant.
 
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Old 06-13-15, 11:40 AM
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A gradual decline in performance is indicative of a low refrigerant charge.
Don't forget to check the filters too as they can impede the flow of air.
 
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Old 06-13-15, 04:14 PM
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I swapped the large panel filter inline with the air flow, as far as I know that's it. Thanks for the input, looks like it's time to get an AC guy out and hope for the best.
 
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Old 06-13-15, 05:00 PM
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If everything else kicks on,including compressor,then all it can be is refrigerant.
 
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Old 06-13-15, 06:57 PM
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One other thing you can check is the return duct in the attic. If it has come loose and drawing in hot air the supply air won't be cold as it should be.
 
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Old 06-15-15, 09:29 AM
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He said outdoor condenser discharge air was ambient temp; therefore, it is not drawing hot air from the attic.

Indoor temp-drop is only 10F; should be 19 to 20F if indoor humidity is around 50%. There can be a lower temp-drop if the humidity is high, however, then the condenser discharge air would be hot, not near ambient temp.

I'd say it is 'probably low on refrigerant' or, there is a restriction in the refrigerant system.

Is it a TXV r fixed orifice metering device?
 
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