There is ice on my AC unit.

May 26, 2012 10:05 AM

So my air conditioning is not blowing cold air. I go to the basement to check the unit, and there is about a half-inch of ice on the main pipe leading out of the unit. Help.

I know I need to call a professional, but it being a holiday weekend, I'd like to avoid that until Tuesday, if possible. I've shut off the heat pump, but I'm curious as to why this happened, and how, if possible, I can fix it myself.

posted by 4ster to home & garden (15 answers total)

Are the heat-exchanger fins (in the outside unit) dirty?
posted by Johnny Wallflower at 10:10 AM on May 26, 2012

This is really common actually. If air flow is obstructed, then the unit can freeze up which restricts air flow even more and so forth. Turning the system off and letting it defrost may help. You may need to clean the coils/fins inside the condenser unit (the one inside the house, the piece outside is called the evaporator). I've used a hair dryer to melt the ice before (this may not be a good idea)

The air flow problem may not be at the condenser, but that's where it's always been for me. Your pipes may be clogged up or kinked somewhere else. If you've forced some vents closed, maybe open em up.
posted by RustyBrooks at 10:12 AM on May 26, 2012

I used to live in a rental with the cheapest possible AC unit. It would freeze up any time I ran it for too long, or at too low a temperature. I'd turn it off til all the ice melted, and always seem to work fine afterwards.
posted by duien at 10:16 AM on May 26, 2012 [1 favorite]

Either its clogged/dirty coils or filter, or it's low on Freon.
posted by topher74 at 10:27 AM on May 26, 2012 [4 favorites]

Whatever you do, DO NOT chip off the ice with a screwdriver or something similar. I am just saying.
posted by elizardbits at 10:40 AM on May 26, 2012 [1 favorite]

Whatever you do, DO NOT chip off the ice with a screwdriver or something similar. I am just saying.

I'll have to remember that for next time.
posted by 4ster at 10:52 AM on May 26, 2012 [4 favorites]

Turn it off and let the ice melt then see about changing the filter. Changing a filter is really easy but if that doesn't work then you might have to wait until Tuesday.
posted by Fiery Jack at 11:00 AM on May 26, 2012

You can use a hairdryer to melt the ice if you want it to go faster. But yeah, don't chip at it.
posted by OnTheLastCastle at 11:19 AM on May 26, 2012

Worst possibility: Your coil may have a leak, in which case the entire coil will need replacing. If it is necessary, make sure to ask your repairman to install a new coil with a good warranty.

Two years ago, I had the coil replaced, but unbeknownst to me the repairman installed a cheap one with a one-year warranty. Guess when that one failed? A little over a year later. I had a different repairman install a new coil that came with a 10-year warranty. No problems so far.

Moral of my sad tale: Ask about the warranty.
posted by Fleebnork at 12:22 PM on May 26, 2012

Everyone's got a great handle on this. Check for flow obstructions you can do something about yourself (dirty filter, closed vents, that sort of thing), and if it recurs, have someone check for low Freon and clean the coil if necessary. Oh, also make sure you're not buying too restrictive an air filter. Some people get filters that claim to filter out allergens or whatever, and if your system is already marginal, that can push it over the edge into freezing up.

The cheap chintzy blue filters will do everything that your A/C requires of it, which is to filter out the hair and large dust particles which will coat everything in the path of airflow. They don't restrict flow nearly as much as some of the more expensive filters do.
posted by wierdo at 1:24 PM on May 26, 2012

It's possible that you had the thermostat turned down too low for the unit to function properly. It froze the pipes so now there is restiction in the pipe. Can you put warm water through? I'm not sure what kind of unit you have. The HVAC friends I have has always told me to remember to introduct hot water into the coils every now and then to prevent freezing. Good luck.
posted by Yellow at 5:24 PM on May 26, 2012

If you let it thaw out, check on it and make sure the melt water is running out of the unit, like it should, and not leaking into the living area because of an ice dam.
posted by Good Brain at 5:28 PM on May 26, 2012

I had this exact thing happen back when I lived in Badly Insulated Condo (during a heat wave no less!). It turned out to be a super-clogged filter - I lived with three cats at the time. Filter replaced, no more ice, cold air once more!
posted by Rosie M. Banks at 5:35 PM on May 26, 2012

It's possible that you had the thermostat turned down too low for the unit to function properly. It froze the pipes so now there is restiction in the pipe. Can you put warm water through? I'm not sure what kind of unit you have. The HVAC friends I have has always told me to remember to introduct hot water into the coils every now and then to prevent freezing. Good luck.

It doesn't work this way. The thermostat just controls on and off.

It might be a clogged filter, but it is probably a low charge of refrigerant. If air is flowing poorly because of a clogged filter, there won't be enough moist air traveling across them to generate all that ice. The coils could get frosty, but a buildup of ice is more likely a low charge.
posted by gjc at 5:49 PM on May 26, 2012

Do you live in an area with cottonwood trees? The cottony seeds from those things are great at clogging up ACs.
posted by Ostara at 7:45 PM on May 26, 2012