Return and supply-temperate difference 13-14 deg


Old 08-22-16, 03:43 PM
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Return and supply temperature difference 13-14 deg

Hello, my AC remains at 73-74 throughout the day and most of night even though thermostat is set to 70. Inside humidity is at 54-55%. Outside temp at around 10am is in the 80s and rises to 96 at hottest point.

I have an AC maint contract and maint was done a few days ago, and tech said all was fine. However, unit did not behave like this last summer. It would go to 70 during day if I set to 70 or 69 at night if set. Now it's midnight and it still does not drop to 70.

I tested temp at return and various vents from closest to furthest out from unit, using a digital thermometer w probe. The temp difference ranged from 13-14 degree from return to the various vents tested.

Is this normal, or is the unit with possible issues?

The AC unit is a Trane 20xi

Would greatly appreciate any feedback.


Last edited by RedZ06; 08-22-16 at 04:51 PM. Reason: Typo.
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Old 08-22-16, 04:08 PM
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Welcome to the forums!

I have relocated your thread to the Air Conditioning section.
Old 08-22-16, 09:33 PM
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13-14 degree split is a little too low, you want 16 at least.
Old 08-22-16, 10:02 PM
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Welcome to the forums.

A agree.... the split is too low.
Since the registers are so close in temperature it appears that the ductwork is insulated pretty well.

Has the filter been serviced ?

Basic maintenance would not include checking the refrigerant charge but it may be required in your case.
Old 08-23-16, 05:18 AM
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Waht is the temperature of the attic. Extreme temps cause big losses.
Old 08-23-16, 12:28 PM
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Thanks all for your input. I replaced filter on day of maint <7 days.

Attic temp is currently at 90 and Outside at 94.

Old 08-23-16, 07:22 PM
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That unit has 2 compressors. A small one and a large one.

I would try to prove that the high speed compressor is kicking in when the cooling demand is greater than 2 degrees.

If you stand next to the outdoor unit while someone turns on the thermostat to cool mode with a 1 degree demand and listen to the unit run then have them increase the cooling demand to 3 degrees you should hear the unit run louder.
Old 08-24-16, 10:57 AM
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The indoor humidity is the biggest factor affecting the indoor temp-split; CFM airflow has a lesser secondary effect.

At an indoor 74F dry bulb & 55% RH that is an indoor wet bulb of about 73F, therefore the indoor temp-split should be around 19F; not 13 or 14F.

The higher the indoor humidity above 50% the lower the temp-split; at 71F WB or 86.5% RH the temp-split is only about 11F.

If Tech added refrigerant it could be overcharged now...
Old 08-24-16, 07:52 PM
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Tech came by today and checked charge and said it needed some. Now it's cooling again to 70.

I also lowered the humidity to 50% tonight and will run it like that moving forward.

Greatly appreciate all your assistance.
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