Hissing central AC evaporator

markiz41 · Jul 2, 2016

The unit is off and has been for several hours after the evaporator and suction line froze up. Now that the ice has melted off, I can hear a slight hiss and it's constant. Tough too say where it's coming from. Can't see any oil spots, but all I can see is the front side anyway. Safe to assume the coil is leaking? Thanks.

Bob · Jul 2, 2016

UNLIKELY, unless you've damaged it.

MOST likely, pooled condensed refrigerant is flashing to gas as the evaporator temperature rises.

Texasmark1 · Jul 2, 2016

Why did it freeze? Dirty filter or coils? Blower stopped blowing? Or did you have a leak and the leak caused the freeze and you are hearing the leaking gas that caused your problem.

Might get something for leak detection and chase out the sound. These things do develop holes/cracks over time that allow the freon to leak out.

Geo-TH,In · Jul 2, 2016

Texasmark1,

Usually a frozen coil is a good sign of all the things you listed. If it's a cap tube system and cold nights, it could cause it to ice up. Especially if it's a tick low on gas.

The Hissing sound is most likely liquid freon inside the evaporator changing to a gas. When it froze up the liquid wasn't able to change to a gas.

My dad's rule of thumb is if the suction line has condensation on it, Freon levels should be close enough. If the coil is frosting up while running on a warm day, good chance you are low on gas, providing all else checks out good. geo

markiz41 · Jul 2, 2016

Tough to say. The coil could use some cleaning, the filter's fine. I guess I'll put the gauges on it and see if I get good pressure readings. It is still hissing as I type and I would hate to add expensive R22 to it if it'll just vent it out fast.

da.bees · Jul 2, 2016

You didn't give a measurable line but I assume the hissing has gone on for more than a few hours. In that case I would think you are hearing something besides the ac coil. A leak large enough to hear will drain a residential system within 4 or 5 hours or less. I would leave the blower on over night and see if it will cool when you turn compressor back on.

Texasmark1 · Jul 3, 2016

My first rule of thumb has been the sweating suction line at the compressor, even on a low humidity day, course length and whether insulated or not could change things somewhat; just takes a second and nothing is required for the data point.

I always had a problem with the freeze up caused by low freon as it competed with over filled and that confusion distorted the initial quick check evaluation.

Agree on the cooling cycle making funny noises internally.

Course if his freeze up was due to low freon, the hiss was/could have been, his clue to the fact that he was loosing gas.

Appreciate your comments.

Geo-TH,In · Jul 3, 2016

Texasmark1, If he is losing gas fast enough he can hear it, good chance it will never freeze up again. It will be out of Freon. I've never heard a Freon leak, unless I just ran a screw in a copper line. Did that once. Geo.

Texasmark1 · Jul 4, 2016

Back when I was much younger, got a call from a friend for advice on what to do. Back then the freezer was just a coil formed aluminum plate with a door on it inside the single door refrigerator. He had ice buildup that he thought he would remedy by ice picking it away. He solved his ice problem sure-nuff. Grin

Hissing central AC evaporator

markiz41

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Bob

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Texasmark1

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Geo-TH,In

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markiz41

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da.bees

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Texasmark1

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Geo-TH,In

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Texasmark1

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