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Old 05-21-2013, 05:56 PM   #1
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A/C blowing cold but not lowering temp


My A/C is blowing out cold air (right now register is 45, return air is 72, outside temp is 86) but the most I can do is maintain current temperature once the sun is up. If overnight I let the temperature go to 78 I can't get it to go below 78, if I keep the house at 70 it can maintain 70 all day this would be for example when the outside temp it 86 degrees like it is now.

Last summer I had the same situation, if I kept the temp at around 70 overnight it maintained it all day even with 105 degree days that we had a few of last year. That was before I found that I had a leak in the system and my inside coil needed cleaned. I had the leak fixed and cleaned the coils and my airflow now feels about twice the output that I had last year but the same issue persists.

I do know the system does not have any leaks now I just had it checked to be sure and it has not lost any charge since the repair. The system is 16 years old so I know it is not very efficient and I should not expect too much more service out of it, but I do need to get one more summer out of it. Prior to last summer it was able to lower the temp in the house fairly easily so I am not sure what the issue could be. Any input on things to check out is appreciated.

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Old 05-21-2013, 06:45 PM   #2
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A/C blowing cold but not lowering temp


Sounds like an insulation problem.

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Old 05-21-2013, 07:32 PM   #3
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A/C blowing cold but not lowering temp


27 degrees between supply and return points to overcharged or still low on air flow.
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Old 05-21-2013, 08:08 PM   #4
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A/C blowing cold but not lowering temp


Is the air filter dirty.
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Old 05-23-2013, 07:03 AM   #5
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A/C blowing cold but not lowering temp


Sounds like a serious airflow problem. I don't think the air would be that cold if it was moving across the coil properly which would explain why you have very cold air and a warm house.
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Old 05-23-2013, 05:23 PM   #6
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A/C blowing cold but not lowering temp


Yep description definitely points to a clogged air filter/ airflow obstruction. 27 degree Delta-T is pretty high.
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Old 05-23-2013, 05:48 PM   #7
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A/C blowing cold but not lowering temp


The air filter is clean, the one in is about 2 weeks old. Just yesterday the blower did start to make a rattling/whining noise occasionally. It lasts about 2-10 minutes then goes away. I narrowed it down the blower as it still makes the noise if the A/C has been off for some time (1 hour +) and have the blower on. I'm imagining it is probably the bearings going. I'm going to pull the blower out and check if anything is in there that could be causing the noise other than the blower itself. At the beginning of last summer and before then the A/C had no issue cooling the house down on 90 degrees day. Nothing has changed with the duct work or the insulation in the house. If the bearings are bad am I correct in thinking that the blower is more than likely not putting out the airflow it should?
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Old 05-23-2013, 06:17 PM   #8
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A/C blowing cold but not lowering temp


That is true. Usually with that temp split the coil will freezeup within 15-20 minutes so I am surprised it runs like that for long. Maybe your thermometer is inaccurate. In 34 yrs of being in biz I have never seen a temp below 48F at a register. 50 is normal. Good possibility that your compressor is worn due to it's age. Can handle the workload when the Sun is lower. It could be a combination of your fan slowing down giving you the extra low supply temp AND the compressor may be only pumping 80% so you are getting cold air but not the literal amount of cooling in BTU's. That could explain the coil not freezing quickly and if you live in a dry climate that helps not freeze it up. Would need a skilled tech to check the compression ratio on a day with the Sun out and lots of techs don't even know what compression ratio is but some do. If the valves are worn it loses compression. Will also result in a large/huge electrical bill as it is not efficient or shutting off. Maybe time to replace it sooner.
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Last edited by yuri; 05-23-2013 at 06:49 PM.
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Old 05-23-2013, 07:22 PM   #9
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A/C blowing cold but not lowering temp


I've verified the temp is correct using 2 different thermometers and the thermostat is only a couple degrees off the return air temp. The thermostat sits about 6 feet from the main return. The coil doesn't freeze up at all inside or outside even if it has been running a few hours. I know the system is due for replacement, which unfortunately is not an option right now. I need to get about one more year out of this one. In either case something is definitely wrong with the blower. If need be I'll replace it, then see if there is an improvement. The electrical side of this I can handle no problem. The other side I don't have the training or certification to mess with so if the fixing the blower does not help I'll either call a pro in again or just live with it until I replace it next spring.

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