AC: air flow stops, but fan is blowing. Give it a break - it starts OK!


Old 07-05-14, 09:45 PM
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Join Date: Jul 2014
Location: USA
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AC: air flow stops, but fan is blowing. Give it a break - it starts OK!

This AC misbehaves - it starts working normally, but then within may be half hour (my guess) the air stops coming out of vents. The fan in AHU always blows when it has to. In a first few minutes after turning just fan on (from Auto) I have normal flow. But then flow ceases as if someone just closes damper. *All vents* seem loose flow at once.

From what I read, the only explanation I can imagine is that the air passages in the evaporator(?) (the cone shaped car-radiator-looking thing above gas chamber with ribs air passes through and cools off) freezes over to the point that ice eventually clogs up all the air passages, thus air flow stops (out of *all* vents at once) despite the fan running.

If I stop AC and take a break (>1 hour), it starts working OK again (that is, until next time within 1 hour when the air flow stops again. , and then air just stops coming out of . The outside unit runs fine, the freon amount is normal (tech. checked that)

Unless you can offer other reasons, is such freezing possible? If so, why did it start doing it (never did for years before), how to make sure this is the case, and then, of course, how to fix it? I'm a handy man, but to fix the problem I have to understand the problem, and as of now I don't.

Thanks a lot in advance to experts in HVAC systems here!
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Old 07-08-14, 05:01 AM
Join Date: Feb 2014
Location: USA
Posts: 2,104
I would clean the A coil.
Old 07-08-14, 05:27 AM
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If the airflow gets severely reduced only when the A/C (compressor) is running, then the evaporator is almost certainly icing over. There are two possible causes: low airflow or low refrigerant. As skaggsje mentioned, check/clean the evaporator to make sure it's not restricting the airflow. If you still have the problem after cleaning the evaporator (or if it is clean to begin with), then you probably have a leak in your A/C system and you're low on refrigerant.

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