We can’t seem to help ourselves. We push the elevator button even though it’s already lit. It’s the same thing with the thermostat. We crank the thermostat down to arctic temperatures in the hopes that it will cool faster. I don’t know if it is misplaced optimism or simple impatience that motivates us. I suppose it makes us feel like that at least we’re doing SOMETHING to make things happen. I can’t speak for the elevator, but I can tell you that playing the Air Conditioning Limbo game (How low can you go!) can actually damage your AC unit. So QUIT IT!
I found the picture below on Pinterest and thought it was hilariously on point. Though I have a couple of issues with it. The first issue being that it is set really high for the warning. You should be able to get a LOT lower than the setting shown without freezing up the unit. I also think “die” might be overstating a bit. I don’t know the exact circumstances of the photo. This thermostat may be located in hell…Pinterest didn’t say. But the gist of it is true: an AC unit CAN freeze up if it is set too low.
The typical AC unit uses refrigerant and compressors designed for medium temperature refrigeration. Unlike low temp refrigeration systems, like your freezer, your AC unit is not designed to take your space into freezing temperatures – not even close! An AC unit is happiest creating space temperatures no lower than 68 degrees fahrenheit. I know some of you out there are all, “I keep MINE at 66 and it’s FINE!” OK, sure, but you’re walking the line, tempting fate and living dangerously. If that’s your jam, proceed if you must.
At lower temps, the unit can freeze up – which literally means having ice or frost form on the coils and/or piping. Though I’m sure some of you are saying, “YES, freezing sounds great! Exactly what I was going for.” Unfortunately, a frozen AC unit cannot effectively cool your space, or you, and it can damage your compressor. So you’ll still be hot and your thermostat limbo may result in a significant repair bill, or early death of your AC unit, which are definitely NOT great.
There are other potential causes of your unit freezing including insufficient air flow (dirty filter, broken fan, blocked or dirty coils, etc.) or insufficient refrigerant in the system. These are issues that are usually addressed during your annual maintenance visit. If you find your AC unit frozen or frosted, the first thing to check is your thermostat setting. If you got antsy and lowered it below the 68 degree threshold, shame on you! Turn the cooling off, leave the fan on, let the unit melt. When you turn it back on DON’T put it below 68! If the thermostat setting is within normal range and your unit is still freezing up, or you’re not getting cool enough, check your filter. If that’s clean, it’s probably time to call your trusty AC technician because something more serious is afoot. By having the unit checked out at the first signs of trouble, you could save yourself the cost of a larger repair later and avoid serious damage to your unit.
So, if it makes you feel better, go ahead and push that elevator button twice. But stop messing with your thermostat, or we’ll have to come over there and lock it on you!
Alex Trodder says
We have a problem with insufficient air flow with our air conditioning unit. When our home was built, it had an unfinished basement. It has a central air unit that is sufficient to move enough air for both floors, but the ventilation that was installed was only designed without the basement being used. Our condenser constantly freezes over, just like in the picture from your post. Make sure that your consult with a HVAC contractor before you finish a basement to ensure that you have the proper ventilation installed to avoid problems like this.
Brandon says
The place where I work (outdoor mall) I’m pretty sure has a pretty big commercial air conditioner. I live in denver where the hottest it gets is just above 90 degrees. She said that running below 72 on a 90 degree day will “overheat” the air conditioner and it will go out. Is that true? Or does she just like it at 72, which is what I suspect. Thanks for your time.
Karen Lamy DeSousa, Advance Air & Heat says
HI Brandon-
A properly-sized AC unit in good condition SHOULD be able to go below 72, even on a 90 degree day. However, if your AC unit is too small for the space it is attempting to cool, or it is really old and/or not well-maintained, those factors could contribute to it’s inability to reduce temps below 72. I hope that helps!
Cesar says
I learned that on the summer of 2016 in Mexico , the AC unit is a Mini Split , witch comes with a remote (and can only be controlled by a remote) companied by ether Prime or Mirage and they use Celsius instead of Fahrenheit. It comes with Heat , Cool , Dry , Fan , Feel and Fan speed of Auto , High , Medium , Low , but it doesn’t have a energy saver ( when cooling stops , fan stops ) , and comes with Swing Option , some comes with Turbo option , witch makes the fan speed even higher than higher.
The range is a bit different for some module but practically the same principles
16-30 , 16-31 , 16-32 C , The 16-30 C is common.
Conversion of temperature 16 C (60 F) , 17 C (62 F) , 18 C (64 F) , 19 C (66 F) , 20 C (68 F) ,
21 C (70 F) , 22 C (72 F) , 23 C (73 F) , 24 C (75 F) , 25 C (77 F) , 26 C (78 F) , 27 C (80 F) , 28 C (82 F) , 29 C (84 F) , 30 C (86 F).
For some reason , some people find mini splits much colder at the same temperature than those typical AC Central System.
But unlike what you said , Putting the AC below 20 C (68 F ) will damage its chip set and possibly freeze up the unit as you mention on your vlog post.
Patrick Salis says
Wonderful article! I think there is a little more to it though than merely temperature. Humidity is actually a bigger issue. In a warm, humid climate, the outdoor A/C unit is more likely to frost over, especially if the aforementioned temperature is set too low. In a drier climate, there is less moisture that will be manipulated, regardless of temperature.
Great article though. As an air conditioning contractor, I will definitely pass this information along to my clients.
Debbi Overly says
This article isn’t true at all. My husband works in the hvac field and said many customers keep their ac on on 62 or even 60. Even window units can go 60 or below just fine. We’ve had 3 houses with whole house ac and kept it around 65 six months of the year with no issues.
Karen Lamy DeSousa, Advance Air & Heat says
Some units will tolerate the lower temperatures. Trane, for example, advertises that they run their units in crazy situations. I even saw one that was still running encased in a giant block of ice. However, just because you can, doesn’t mean it’s good for your unit. If you want unit longevity, efficiency and reliability, it’s best to keep temperatures within design ranges.
Glenn says
I respectfully disagree.
I believe your statement is very true for your specific location.
However, as you move further south and into more humid and hot areas – fuh-get-about-it.
For example, in Texas, run your AC below 68 degrees in August and you will very quickly be without AC.
So remember, where you live may be the center of your world, but everybody knows it’s really Austin 😉
Just my 2 cents.
Karen Lamy DeSousa, Advance Air & Heat says
And here I thought Massachusetts was the center of the universe… Thanks for the 2 cents Glenn!
Jon says
Nope no way.he is one of those guys who dks
Matt Gillespie says
Is it better to leave blower fan on auto or leave it on on witch is more efficient acts better for unit ? Thanks. Matt G
Karen Lamy DeSousa, Advance Air & Heat says
As a general rule of thumb, I generally recommend leaving the fan on auto, which means that the fan will run only when the system calls for either heat or cool (depending on the type of system you have). The exception to this recommendation would be for commercial systems that also bring in fresh air. In that case, you’d want to leave the fan on all of the time to circulate fresh air into the building even when the system is not actively heating or cooling. The typical residential unit does not provide fresh air, so most choose to leave the fan in auto. The only advantage to leaving the fan in the ON mode for a system without fresh air would be to continually circulate the inside air through a filter to provide additional air filtration. If you choose to do this, I’d recommend more frequent filter changes. So long story short, if you have a system with fresh air, go with fan ON. If you don’t, save a little energy by putting the fan in Auto. Hope that helps!
Pat Harris says
I have heard to correct the intake air flow a hole can be made in the intake vent to increase air flow so that the unit will not freeze up. Is this true?
Karen Lamy DeSousa, Advance Air & Heat says
Hi Pat- I would NOT recommend that. If you do not have enough intake or return air, it is a sign of a ductwork problem. Cutting a hole in the return duct will allow more air to return to the unit, but not the air that SHOULD be returning to the unit. Your HVAC system is designed with balanced supply and return air for the various areas of your building. Balancing supply and return air gives you proper air circulation inside the space and for the unit to operate. If you just cut a hole in the return duct, you will increase the air to the unit, but not in a way that considers proper circulation. Depending on where you cut the hole, you could also get return air that is not conditioned, creating an even greater demand on your unit instead of correcting the root problem of lack of sufficient return air.
Samantha says
I live in Florida where it’s like the 9th Circle of Hell right now. My boyfriend keeps cranking our A/C down to 67 and I keep TELLING him not to do this because he will freeze the system up and damage the compressor. But…in this kind of heat (reaching almost 100 most days until the rains cools it off…for a minute!), will it still freeze up? Wouldn’t the temps outside keep it from freezing up?
Karen Lamy DeSousa, Advance Air & Heat says
First, thank you for the laugh, Samantha! My sister lives in Orlando and my last visit truly DID feel like the 9th Circle of Hell! 🙂 To me the question is this…does your boyfriend really WANT a room temp of 67 degrees, or is he just trying to get the unit to cool “faster” by lowering the setpoint? I suspect that your AC unit is probably running at full capacity in that “Circle of Hell” heat, so it won’t cool any faster if you put it on 67, than if you put it on 70. It will just keep running at full capacity longer to try to get the temp down to the most likely IMPOSSIBLE room temp of 67. If your room were an insulated refrigerated box, you could get it that low, otherwise you’re just beating up your poor innocent AC unit for no reason! Be nice to your AC unit and it will be nice to you. Couple of suggestions, if you’re shutting the unit off, or using a really aggressive setback when you leave the house, it will take FOREVER to cool the house back down. Leave it running at a temp that’s maybe 5 degrees higher. If you do that, and your AC unit is still not getting temps down to 70 after an hour or two, your unit might be undersized or in need of a tune-up.
Steven says
I’m trying to determine if my thermostat is needing to be replaced. I recently had our unit serviced and everything looks good. According to our AC guy, our unit is a bit under sized (by a 1/2 ton) for our home and has a hard time keeping up on really hot summer days. So, I guess I can understand why it runs solid late into the evening. I am up really late tonight and noticed the unit coming on and shutting off frequently, BUT the thermostat is set on 70 and the room temp shows at 68. Is there a reason the unit should keep kicking on when the thermostat is set two or three degrees above the actual room temp? Could it be my thermostat needing replaced? It’s an old Honeywell TH5110D1022 commercial stat.
Karen Lamy DeSousa, Advance Air & Heat says
It sounds like the thermostat would be a good place to start. The unit shouldn’t come on unless the temperature is OVER the setpoint of 70 degrees. It’s not uncommon for a unit to overshoot the temp setpoint. Once it’s on, it should run nice and smooth until it gets to setpoint or slightly below. A degree or even two below setpoint is not that unusual, but it IS unusual for the unit to go on/off frequently. It should not do that as it is not good for the unit to run that way. It can cause damage. I would recommend getting the tstat and the unit checked out as soon as you can.
CSR Girl says
My boss keeps setting the unit in MY office to 60 degrees! I keep telling him NOT to do this, because (a) the room will never get to that temperature, and (b) he’s killing the unit. We are in Tupelo, Mississippi in July. It is 103 right now, and it’s 9:44 am. I know I’m right, but I can’t make him understand! HELP! I’M FREEZING MY BUTT OFF!!!
Karen Lamy DeSousa, Advance Air & Heat says
You poor thing! You must have to wear mittens! Please feel free to forward the article (and I’m sure you could also source plenty of others on the same topic as well) to your boss with my blessings. I hope that it works for you!!
Virginia Thompson says
I have a 3 year old goodman s/c unit with 5 kw heat. It was working great up till one day it stopped blowing strong enough. The freon levels are good, coil is clean, blows cold but barely strong enough to cool the house. The pressure of the air is to that of a trickle. I can barely feel it standing under the vents. It also blows strong sometimes and not at all other times. What could be wrong it other than the X13 motor that my a/c tech keeps refusing to replace and is under warranty. The other issue is that it cools at 74 degrees but it I try to put it down to 73 or 72 degrees the temperature goes up to 75 or 76. What could that be.
Karen Lamy DeSousa, Advance Air & Heat says
Hi Virginia – The X13 motor is an ECM style motor which can be tricky to troubleshoot. The motor essentially controls it’s own speed by using a constant torque set to manufacturer’s specifications. It does sound like a motor malfunction is your culprit here. The good news is, warranty parts can be installed by ANY contractor, not just the original installer. The warranty follows the part no matter who replaces it. Since labor is generally not covered after the first year, using a different contractor wouldn’t hurt you at this point. If you’re in Southeast MA, give me a call! 508-763-3738
Laura Mathews says
I live in Houston, Tx.
Well a few day’s ago the pan for our AC unit was overflowing water into my son’s room.
Lanlord came over and cleaned out pan.
Said it had some debris in it and the line was backed up.
The next day we heard a loud noise where the filters go in the hallway.
Landlord came over and of course no noise!
She replaced filters.
That night I heard a different sound coming from outside unit.
I noticed that night It wasn’t as cool in my house.
I had temperature set at 70°
She said it was too low to set it, although that’s what it has been set at forever.
I had the temp set to 75° to see how it would do. The temp was up to 80°.
I went and looked at unit outside and coil to AC was frozen.
I turned unit off.
She thinks it is because I had it set to low, but it froze coil outside while set at 75°
Help!!!
What is your opinion??
Thank you
Laura
Karen Lamy DeSousa, Advance Air & Heat says
It sounds like there are other issues going on with your unit that require the help of an HVAC technician to troubleshoot and figure out what’s going on. 70 degrees should not be too low to set the AC. It could be an issue of air flow, refrigerant or something else. An HVAC technician has to tools to figure it out and repair.
Laura says
I live in Florida and it’s been mid to upper 90s outside lately and extremely humid as well. I keep my AC set at 76, but it hasn’t been able to reach that temp during the day. It’s been trying to keep up but only getting to 79 or 78 degrees, so it’s also running all day long, literally nonstop. The air coming out of the vents is cold, it just can’t keep up. Am I setting it at an unrealistic temperature for it being 95+ degrees outside, or does it sound like my AC unit is about to crap out? Any advice is much appreciated, thank you!
Karen Lamy DeSousa, Advance Air & Heat says
The temp you’ve set it at of 76 should be attainable if your unit is sized properly, in good condition and your building is properly insulated. The units are factory tested at 90+ degrees so those outside temps shouldn’t be a problem, and you should be able to get down to low 70s temps no problem. However, if the unit is too small, it might not be able to do it. Also, if the unit needs maintenance or repair, that could account for poor operation. In order to work at it’s peak, it should be professionally maintained at least once per year. More if it’s used heavily. I hope that helps!
ash says
I have lived in my apartment for 3 years. The central air unit is 15 years old. I like to keep the thermostat on 68 degrees. My unit has never frozen up and has worked well. It did stop working a few weeks ago. The thermostat was not lit up. The repair guy had to get a piece to fix it and it is working again. However, those in our complex got a notice stating that(for those of us who run our 15 year old units lower than 72 degrees and if our central air unit tears up, we will have to pay $2000 to have it replaced. This is a concern for me. Is this realistic? these are old units that are over 15 years old and are no longer under warranty.
Karen Lamy DeSousa, Advance Air & Heat says
It sounds like your complex is trying to reduce the strain on your AC unit in an attempt to extend its life. 15-20 years is the typical lifespan of a unit, so it is prudent to budget for a replacement at that point. Limiting the temperature that the AC runs at to 72 will help the unit to run less often and may help it last a little longer. If you need additional cooling and don’t want to go against the policy, you could try using fans to keep cool. They don’t use a lot of energy and they really help. Shut them off when you’re not in the room, because they don’t cool the room, they only cool you! Hope that helps.
ash says
addition to my last post
I have been here in this apartment for three years. I have never even seen the HVAC guy until the air went out. My unit, nor any other unit in my complex are maintained. The guy is only called out when there is a problem.
Bill Gagric says
Good article, one thing to take into consideration. All TXV (thermal expansion valve) manufacturers that I am aware of, will tell you not to run system with return air temperature 68 degrees or lower. TXV is a valve that controls refrigerant flow to the inside evaporator coil. With that said, your thermostat really should not be any lower then 70 degrees, any lower and you will shorten compressor life.
Ann says
Thanks for this article and Q&A. It sounds like I should be able to lower my nightime temp to at least 70F. My A/C man told me not to run it below 73 to be safe and we are dying at night as we like to sleep cool (preferably 60s). He said that that the compressor runs 40 degrees below the thermostat, so anywhere from 72 and below we would risk freezing the coils. Is this right? Or is 70 really safe? I was told this after expensive repairs and don’t want to make the same mistake twice. Before I was running it in the 60s. Would 70 be ok? I’d like to run it at 72 during the day and as low as it is safe at night – maybe 70? I’m miserable at 73F!
Karen Lamy DeSousa, Advance Air & Heat says
By the rule of thumb, you should be fine to set your thermostat at 70 degrees, but to be safe, you could look up your particular unit’s operations manual online and check their specifications. On the unit should be a tag that has the manufacturer’s name and the unit model number. If you plug the first three or four digits of the model number along with the manufacturer’s name into a Google search, you should be able to find the manual. That will tell you how YOUR unit was originally designed. If your contractor has made modifications to the unit, or if your unit is older and having issues already, there may be other considerations. You could try lowering one degree at a time. Try 72 and see how it operates. Keep in mind that the hotter it is outside, the harder your unit has to work, and the greater risk of freeze-up.