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Q about A/C Unit


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14-Oct-2008, 11:31 PM #1
Q about A/C Unit
My AC unit in my apartment always freezes up (pipe is iced up) every summer. It also seems to freeze up if i have the ac off for a while, like when I went on vacation I turned it up to 75. It has been freezing up at least once a week now.

All the maintainence do from what I know is add free-on or charging it up... The dam thing outside looks like it's from 1970s (and the maintanence guys are older than dirt, no offense to old guys here) and I am tired of being in high 80s when I'm going to bed...

is there something i should look for so I can tell them to replace the ac unit?
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15-Oct-2008, 01:26 AM #2
Not sure what you mean is freezing up. The freon pipes can't freeze. Are water pipes freezing?

If you are just talking about ice formation on some pipe, the best way to deal with that is to cover it with wrap foam insulation that will keep the cold in and the moisture out.
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15-Oct-2008, 06:39 AM #3
is it clean? if not that can cause it. those window units regularly need the filter cleaned
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15-Oct-2008, 11:19 AM #4
It's not a window A/C unit.

The pipe I'm talking about is a pipe that seems to come from the AC/Fan unit outside and into the unit inside. Both the pipe outside and inside freeze up, like how ice is formed in your freezer. Though I have notice this happening on hotter days.

I will take pictures to show you what i mean should have done that yesterday but the pipe wasn't fully frozen then (spots of ice around the pipe)
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15-Oct-2008, 08:24 PM #5
is the part of the unit outside clean?? I am by no means an expert but I am guessing if that gets dirty the same problems will happen as a window a/c
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16-Oct-2008, 02:19 AM #6
I have an old unit and it freezes up. The fins around the condenser sometimes look like a block of ice. This happens about once every couple of years. According to the repair guys, I have a slow leak of freon. They fill it up, it cools better than ever, and I am good for another two years. Hope this helps.
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17-Oct-2008, 03:33 PM #7
I own a rental place where the AC has frozen up a number of times. The most common cause was a dirty air filter. It causes slower air movement around the evaporator and the moist air would freeze. I have tenants who forget or can't figure out how to change the filter, even though I keep a supply there for them. So they call, I go over, thaw it out with a hair dryer, put in a new filter and am good til the next summer.

And the other reason for it is low freon. If it ices up again, I call service and they add some refrigerant. They never find the leak, say it must be too small.

It's freezing on the intake pipes? Maybe go to the hardware store and buy a foam tube to insulate it. It might help keep the ice from going further down into the evaporator. Or look into a dehumdifier to take the moisture out so the apartment air isn't so humid ... but I bet a dehumidifier 24/7 might take as much power as the AC,
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20-Oct-2008, 08:37 AM #8
The freezing is almost always the unit being low on refrigerant, though a clogged filter can cause that in extreme cases.
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23-Oct-2008, 09:32 AM #9
Seeing ice form on a pipe can simply be condensation freezing. When the evaporator freezes, then airflow through the evap stops [and your room is hot]

All A/C units have some type of monitoring to stop this from happening. On some it is called suction throttling; ie the flow of gas on the low [cold] side is restricted, on others it simply cycles the compressor off. The problem is in whatever controls evap temp.
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23-Oct-2008, 05:28 PM #10
Ice on the pipe can be normal, however if the coils freeze over, that's not normal for any operating mode.
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30-Oct-2008, 07:48 PM #11
There are 2 lines that go to the AC unit, one small (liquid line-high pressure) and a larger one (Low pressure return)

The large one is always prone to collecting ice on the outside due to high humidity and condensation, normally the large line is insulated with a foam sleeve that prevents ice from collecting and also improves efficiency of the system.

If the system is charged properly you should not get any icing near the outside unit where the lines go into it, this is a sign of overcharging, which is sometimes done because the unit is old and can no longer do its job, so these old guys think it is low on freon and overcharge it, it will eventually trash the compressor, maybe you will get a new AC unit this way. :-)

Central Air conditioners in homes or apartments can only get a 10 degree drop across the evaporator, what this means is that if it is 80 degree's in your house, and you put a thermometer in the AC vent that is blowing cool air into the room, at best it will read 70 degree's, and that is if the unit is operating at peak performance. If the house is not insulated properly then you may not get much drop in temperature inside, the AC unit cannot remove the heat faster than it is coming in, so the thermometer trick is an easy way to tell if it is a AC unit problem, or a insulation issue. Use the same thermometer to take both temp readings.

The only other thing it could be is an undersized unit for the dwelling.
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