# Is my AC unit safe to operate this way? **URL:** \ **Category:** Factual Questions\ **Created:** [July 28, 2004, 4:20am UTC](https://boards.straightdope.com/t/is-my-ac-unit-safe-to-operate-this-way/257231 "2004-07-28T04:20:39Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![BobT](https://avatars.discourse-cdn.com/v4/letter/b/8e8cbc/32.png) [@BobT](https://boards.straightdope.com/u/BobT)\ **Post date:** [July 28, 2004, 4:20am UTC](https://boards.straightdope.com/t/is-my-ac-unit-safe-to-operate-this-way/257231/1 "2004-07-28T04:20:39Z")
I have an old wall unit in my apartment (renter). It’s at least 12 years old as that’s when I moved in. What happens is that after I turn it on, ice, or some other whitish substance starts to coat the inside of it. It doesn’t take long for the icy substance to appear, just a few minutes. If I let it go for about an hour, I’ve pretty much got a polar ice cap in my air conditioner. Is there something leaking? Something not good for me? Is this is a sign that the unit is about to die? Is it hurting its energy efficiency, which is pretty bad to begin with. ---
**Author:** ![DMC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dmc/32/18049_2.png) [@DMC](https://boards.straightdope.com/u/DMC)\ **Post date:** [July 28, 2004, 4:30am UTC](https://boards.straightdope.com/t/is-my-ac-unit-safe-to-operate-this-way/257231/2 "2004-07-28T04:30:01Z")
The first thing I’d look at is the filter. Is it clean? If not, replace that, and see if that clears it up. While the coil can get very cold, if you have good air-flow, I don’t think it should ice up as badly as you describe. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [July 28, 2004, 4:30am UTC](https://boards.straightdope.com/t/is-my-ac-unit-safe-to-operate-this-way/257231/3 "2004-07-28T04:30:58Z")
Ice forms on the evaporator coils of an air conditioner for a few reasons, including: [ul] [li]Insufficient refrigerant[/li][li]Excessive cooling capacity (BTU/hr rating) for the area to be cooled[/li][li]Outside temperature too low[/li][li]Insufficient airflow (check filter)[/li][/ul] Given the age of the unit, the first and last items are the most likely possibilities. If the ice is forming as quickly as you say, then cooling capacity is probably not the issue. Definitely remove the front panel and clean or replace the filter, since clogged filters are the number one cause of window AC unit performance problems. ---
**Author:** ![BobT](https://avatars.discourse-cdn.com/v4/letter/b/8e8cbc/32.png) [@BobT](https://boards.straightdope.com/u/BobT)\ **Post date:** [July 28, 2004, 4:34am UTC](https://boards.straightdope.com/t/is-my-ac-unit-safe-to-operate-this-way/257231/4 "2004-07-28T04:34:09Z")
Thanks, I doubt it’s the outside temperature as I live in Southern California and it’s mighty hot here. I took the cover off and I couldn’t even find a filter. So either I’m looking in the wrong place or the filter has disintegrated over the years. I know that this unit has NEVER been serviced since I’ve moved in. But I still need to know if it is safe to operate in this state. ---
**Author:** ![Ms2001](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ms2001/32/18463_2.png) [@Ms2001](https://boards.straightdope.com/u/Ms2001)\ **Post date:** [July 28, 2004, 4:34am UTC](https://boards.straightdope.com/t/is-my-ac-unit-safe-to-operate-this-way/257231/5 "2004-07-28T04:34:25Z")
> [@BobT](#): > > I have an old wall unit in my apartment (renter). It’s at least 12 years old as that’s when I moved in. What happens is that after I turn it on, ice, or some other whitish substance starts to coat the inside of it. It doesn’t take long for the icy substance to appear, just a few minutes. If I let it go for about an hour, I’ve pretty much got a polar ice cap in my air conditioner. Yeah, that’s frost. [This site](http://www.handymanusa.com/questions/airconditioningq.html) suggests that your AC might need a recharge, and that might mean your refrigerant is leaking out: > [@](#): > > You’re right, if the unit keeps freezing up on the first pass of evaporator coils, there must be a leak. (A lower than normal charge will cause the remaining refrigerant to boil off at a lower temperature, below freezing, it shows up as frost on the coil.) ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [July 28, 2004, 4:42am UTC](https://boards.straightdope.com/t/is-my-ac-unit-safe-to-operate-this-way/257231/6 "2004-07-28T04:42:08Z")
> [@BobT](#): > > But I still need to know if it is safe to operate in this state. Safe as in “not going to explode and cause a fire”, probably. However, running it much in this condition can overload the compressor, causing premature wear and possibly failure. Since the ice on the evaporator is a pretty good insulator, you’re not getting much in the way of cooling, anyway. If you can afford it, new units are fairly inexpensive. Be sure to properly size it for the area you intend for it to cool, using a calculator such as [this one](http://www.consumerreports.org/main/detailv2.jsp?CONTENT%3C%3Ecnt_id=85365&FOLDER%3C%3Efolder_id=24131). ---
**Author:** ![BobT](https://avatars.discourse-cdn.com/v4/letter/b/8e8cbc/32.png) [@BobT](https://boards.straightdope.com/u/BobT)\ **Post date:** [July 28, 2004, 5:08am UTC](https://boards.straightdope.com/t/is-my-ac-unit-safe-to-operate-this-way/257231/7 "2004-07-28T05:08:39Z")
Thanks. Since I’m a renter, I am getting on the manager’s case to do something about this. August and September in Southern California without a functioning A/C is not a pleasant thing. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [July 28, 2004, 5:09pm UTC](https://boards.straightdope.com/t/is-my-ac-unit-safe-to-operate-this-way/257231/8 "2004-07-28T17:09:25Z")
I hope you don’t think I’m insulting your brain power or anything, but since I’ve seen this happen _a lot_: Have you set the air circulation to “fresh” or “recirculate”? You almost always want the latter as A/C works mainly by removing moisture from the air, chilling is a very nice side benefit from how that is done. If your A/C is always getting fresh air from outside, it will constantly have to remove moisture from the air and ice build up is more likely. ---
**Author:** ![BobT](https://avatars.discourse-cdn.com/v4/letter/b/8e8cbc/32.png) [@BobT](https://boards.straightdope.com/u/BobT)\ **Post date:** [July 28, 2004, 5:12pm UTC](https://boards.straightdope.com/t/is-my-ac-unit-safe-to-operate-this-way/257231/9 "2004-07-28T17:12:29Z")
Definitely not insulting my brain power. When it comes to home repair, I’m an idiot. I’ve never understood which setting was best. I’ll check when I get home. Regardless, I think the unit needs to get serviced as no repair person has checked it since I’ve been there and during some repairs to the upstairs units, contractors have dropped stuff on the unit and it’s full of dents. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [July 28, 2004, 5:16pm UTC](https://boards.straightdope.com/t/is-my-ac-unit-safe-to-operate-this-way/257231/10 "2004-07-28T17:16:50Z")
> [@ftg](#): > > A/C works mainly by removing moisture from the air, chilling is a very nice side benefit from how that is done. Curious statement. I would argue that an AC works mainly by allowing a refrigerant gas to expand thereby removing heat from it’s surroundings. Dehumidification is a nice side effect of _that_ process. The way you put it sounds like the thing won’t work in completely dry air, which, of course, it will. I agree about the air circulation setting, however. I haven’t seen this on newer units, but older units did indeed have such a switch. Newer units still can draw in outside air, but they do so with a “Fan” setting, typically, which does not run the compressor at all. ---
**Author:** ![BobT](https://avatars.discourse-cdn.com/v4/letter/b/8e8cbc/32.png) [@BobT](https://boards.straightdope.com/u/BobT)\ **Post date:** [July 28, 2004, 5:20pm UTC](https://boards.straightdope.com/t/is-my-ac-unit-safe-to-operate-this-way/257231/11 "2004-07-28T17:20:57Z")
If this is any clue, the frost started to form during a spell of relatively humid weather here in Southern California. Again, home improvement is a foreign language to me, which is why I seek help here. And it’s why I rent. That and Southern California’s median home price of $414,000. ---
**Author:** ![BobT](https://avatars.discourse-cdn.com/v4/letter/b/8e8cbc/32.png) [@BobT](https://boards.straightdope.com/u/BobT)\ **Post date:** [August 5, 2004, 11:03pm UTC](https://boards.straightdope.com/t/is-my-ac-unit-safe-to-operate-this-way/257231/12 "2004-08-05T23:03:21Z")
For those who care and want closure on the saga of my AC unit, the culprit was: lack of refrigerant. Actually, it had close to none left. But now my AC runs again. Of course, it’s cooled off here and I don’t need to run it. Thanks for all the advice.