Window AC units work, but freezes up!?!

Old 08-01-10, 09:28 AM
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Window AC units work, but freezes up!?!


I have a Freidrich Model SL33J30 Window unit that has worked great for 8 years. Normally, I would just turn the thermostat until it shut of automatically.

Just lately, it will not shut off and keeps running until the interior coil freezes over with ice.

I have checked all of the filters and vents and none of them are obstructed or blocked.

I used a volt-ohm-meter and set it for continuity check and placed the leads across the contacts of the thermostat. The circuit is closed and stays closed no matter which way I adjust the thermostat.

Does this sound like a thermostat issue? I found a replacement part online for ~ $60.00. But how can I be certain this is the problem?

TIA to all
Old 08-01-10, 11:50 AM
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Are the blower wheel vanes full of caked dust? If so, clean them one by one (and make sure you vacuum out what drops through the vanes!, ( so it does not get sucked to the backside of the coils! And if you can't and you do not want to try to remove the wheel itself, you might need assistance in having someone hold a vacuum up against each vane, as you scrape each vane with say a screwdriver.), to improve the air speed which, will help warm the coolng coils with roomtemp air, to help keep it from freezing. Unfortunately, you cannot quickly, readily see how the backside of the coils look, to see if the hidden side of any of the coils is blocked. See if the amount of air that blows out seems about the same as it always has, or if it seems substantially weaker. Weaker, can lead to icing.

The thermostat test: I have not had to check one lately, but it may stand to reason that even when the unit is off and warm - on a 1 setting it may be calling for a/c the same as at a 9 setting. (Refrigerator stats are the same way in this regard) The way you would know for sure is to pack ice at it and then see if you can get an open reading across it, as you should then for sure, especially if you turn the stat back towards 1.
Old 08-02-10, 10:33 AM
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I know that central units freeze up if the freon is low, but im not sure about window units.
Old 08-02-10, 12:14 PM
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Make sure the probe for the thermostat is still inserted into the evaporator coil. If it is still inserted test the thermostat by carefully pulling the probe out of the evaporator and placing the end of it in a glass of ice water. (MAKE SURE UNIT IS UNPLUUGED OR BREAKER IS OFF) If the thermostat contacts wont open when set to low with the probe in the ice water the thermostat is faulty.

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