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Old 07-02-2008, 02:50 PM
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AC Line freezing up

My AC is acting like a little bitch. The copper line that runs into the box on top of the furnace keeps freezing.

I'm mechanically inclined and very much a do it yourself type person. This is what I have done so far: I have replaced the air filter, opened a vent that was closed, and I washed out the vents on the outside compressor.

When I turn it on the air that comes out is cold, but after a few hours that line is froze again.

Are there any other steps I can take before I have to break down and call a professional?
Old 07-02-2008, 03:11 PM
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Does the air continue to blow cold or does it stop working?
Most likely it's just condensation freezing over it. You could probably just cover it with pipe insulation.
Old 07-02-2008, 04:10 PM
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Quote:
Originally Posted by Joey P
Does the air continue to blow cold or does it stop working?
Most likely it's just condensation freezing over it. You could probably just cover it with pipe insulation.
The air stops being cold. The pipe was covered in insulation but the ice caused the insulation to burst open.
Old 07-02-2008, 04:20 PM
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One of the main things that causes evaporator line freezing is low gas pressure. If you've cleaned or changed the filters and vacuumed the dust, dirt and debris out of the evap coils (this will be the part indoors with a filter and a fan to blow air over it and through the ductwork) then low gas pressure is a good bet, particularly if the system ran fine last year.
Old 07-02-2008, 04:35 PM
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Our AC exhibited very similar symptoms. Turns out it's a freon leak. So, just seconding Q.E.D..
Old 07-02-2008, 05:03 PM
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I just had the same problem with mine.
After talking to equipment techs whom I work with they had me clean the furnace filters and hose down the vanes on the exterior unit.
Still I got no cold air and the line froze up again.
One of them came over with some gauges and his tank of freon. The pressure was indeed low so he added freon slowly to get it back to normal (it hadn't been serviced in decades). He said it should be good for a couple more years.
He did it for me for free (case of beer actually) but said a heating-a/c company will run a few hundred dollars to add freon to the system.
Old 07-02-2008, 05:38 PM
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Quote:
Originally Posted by Hampshire
He did it for me for free (case of beer actually) but said a heating-a/c company will run a few hundred dollars to add freon to the system.
$299.00 in our case
Old 07-02-2008, 07:53 PM
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A technician is supposed to check for sources of leakage and correct any noted before just adding refrigerant. That was part of the certification exam for type I & II systems years ago.
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Old 07-02-2008, 11:58 PM
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Quote:
Originally Posted by danceswithcats
A technician is supposed to check for sources of leakage and correct any noted before just adding refrigerant. That was part of the certification exam for type I & II systems years ago.
And not only that, if you lose more then a certain amount I beleive they (technically) have to report it to the EPA. Though I could be compleatly wrong on that.

ETA: reading the EPA site it wouldn't apply to a home AC system. It only applies to systems with at least 50 pounds of freon with a loss of at least 15% of the charge in a 12 month period.
Old 07-03-2008, 12:42 AM
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Quote:
Originally Posted by Q.E.D.
One of the main things that causes evaporator line freezing is low gas pressure. If you've cleaned or changed the filters and vacuumed the dust, dirt and debris out of the evap coils (this will be the part indoors with a filter and a fan to blow air over it and through the ductwork) then low gas pressure is a good bet, particularly if the system ran fine last year.
[Emphasis mine]

I hear this a lot, but IME (26 years and counting) the main cause of evap freezeup is low air flow across the evaporator coil. As noted, this can be caused by dirty filters (already checked), dirty evaporator coil (the usual culprit), excessively dirty or failing evaporator fan (rare), restricted supply air ductwork or restricted return air ductwork (rarer still).

However, low refrigerant levels will also cause freezeups. Doubly so because once ice builds on the evaporator coil, airflow basically stops, which kind of snowballs the process.

I have also seen low evaporator air flow diagnosed as low refrigerant charge by inexperienced technicians, since one of the effects of restricted airflow is a reduced suction pressure.

A rough way to test if the problem is low refrigerant charge is to run just the indoor fan without the compressor for a few hours to ensure that all of the ice on the evaporator coil has melted. You can do this by switching the "heat-off-cool" switch to Off and the Fan switch to On on your thermostat. Once you are sure all of the ice has melted, move the thermostat switch back to the "cool" position and immediately check the refrigerant suction line at the outside unit (the condenser). If the suction line at the condenser does not get cold enough to sweat, like a glass of iced tea, within a few minutes, you probably have a low refrigerant charge. OTOH, if the line immediately gets very cold, possibly even forming frost, you likely have a clogged evaporator coil.

For a low refrigerant condition, the repair is to carefully check for leaks (the access ports where the refrigerant gauges are connected is a routine source of small leaks - lines rubbing against nails in the walls or attic is another) and then top off the charge.

For a restricted evaporator coil problem, the remedy is to remove the source of restriction. This is almost always a dirty evaporator coil and involves gaining access to the inlet side of the coil and brushing out the surface debris and then soaking with a self-rinsing coil cleaner. Oftentimes, this operation is followed shortly by a clogged drain line as the debris tries to flow through the line.
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