I’ve been told by apartment maintenance men that, if you run your air conditioner at “too low” of a temperature, it’ll freeze up and not cool the air.
Is this true? If it is, then why does the thermostat permit you to turn it down to that magic temperature at which the unit will “freeze up.”
What causes this to happen?
What’s “too low”? If ice starts forming in the evaporator coil it means the system is not well designed, mainly because the coil is undersized for the cooling capacity of the rest of the system.
An airconditioner that keeps running constantly can freeze it’s own pipes.
Why does the thermsotat go so low? Well, if it’s 71 degrees and terribly humid, you’d like it alot better at 64 degrees with little humidity, which the A/C can do. However, if it’s 99 degrees and humid, and you set it to 64, and you leave a door open or have alot of in/out traffic, you can cause it to run so long it freezes its own pipes.
Saw this last year on my neighbors unit. He left the A/C on 68, his wife had the windows open and went out… and it was around 97 degrees all day. By evening, the sucker was blowing warm air and as it had literally froze it’s own pipes.
Check the FAQ section of A/C websites. “air conditioner frozen pipes faq” or something like that in google.
In simple terms an A/C works by passing air over a cold set of pipes with fins, kind of like a car radiator. Humid air passing over the coil has its humidity lowered as the moisture condenses on the coil. Just as water condenses out of the air on a cold glass or water.
If the coil is cold enough, the water will freeze before it can drip off the coil. If the coil freezes, then air can’t pass through to get cooled.
Define “freeze up.”
I recently got my AC unit replaced; since I live in south central Texas, I NEED an AC unit during high summer. My old unit “froze up” in two different ways:
Due to the humidity, the filter over the air intake tended to have a little condensation on it. Run the AC long enough, at a low enough temperature, the condensation will freeze. Let this happen long enough, and you block the air intake to the point where it won’t draw in any air. You can damage your AC unit by doing this.
In my case, the bearings in the motor were worn, and finally the motor seized up, thus making the AC unit not work… although I get the idea this isn’t what you meant. It did, however, finally influence me to buy a new unit, since the old one was prehistoric to the point where buying a new motor would have been like putting new tires on a demolition derby car…
Mine did.
[My experience is almost all automotive, but the theory is the same]
the part of the air conditioning system that gets cold is called the evaporator. (evap for short) Inside the evap is a liquid that evaporates to a gas*. [Hence the name] when this change of state occurs much heat is absorbed. The heat comes from the warm air being blown across the evap. The heat from the warm air transfers into the liquid / gas refrigerant. This is how you get cold air. When the air is cooled it cannot hold as much moisture so condensation forms on the evap.
Now if the controls for the system allow the evap to get too cold, the condensation will start to freeze and a while a sheet of ice will form across the top of the evap. Air cannot blow through ice so the perception is that the A/C quit working. Actually the contrary is true, not only is the system still working, it is making the ice thicker.
So if you system (home or car) works great for a period of time, and then flat quits, no air from vents, one of the things to look for is icing of the evap. There are many other things that can cause the air to quit coming out of the vents, consult a trained technician to determine which is the cause in your case.
*Used to be R-12 called Freon, now R-134 in cars. Off the top of my head, I don’t recall the mix used in home A/C R-22?
You got it right, it’s R-22.
The word “mix” is probably not the best choice, however, as all of these denote a single chemical, not a mixture. As I’m sure Rick knows, some of the automotive “alternative” refrigerants are mixtures, which is part of the problem with them.
mix? WTF?
OK I call brain fart here. I did not mean mix. I meant the name of the compound used in home systems. :smack:
Gary T you are completely right as usual.
And yes I do know about mixtures in mobil A/C systems.
The most common cause of evap coils freezing up is a low refrigerant charge (due to a refrigerant leak). When the evaporator refrigerant pressure is too low, the coil gets too cold and freezes the condensation on the coil.
Excellent choice of subject! I have most exceptionally recent experience with this, and have an idea or two.
Actually, I’m calling it an “unproven theory” at this point. The refrigerant charge in my A/C unit was perfect. No leaks, no compressor problems, no fan problems. However, I was getting very low-flow warm air from the vents. I noted that bot the supply and return refrigerant lines were warm. I also noted a bit of ice on the line heading into the plenum space.
After running the damn thing on FAN for two days, and watching a non-stop flow of water from the drain line finally come to an end, I’ve got nice cold air. It barely gets above 75 upstairs, and you could ferment lager in the basement (I’ve considered it already).
The primary reason I think that the evaporator froze up? Easy. The return air vents were blocked. I think that the lack of warm air to help melt the ice that was attempting to form on the evaporator was the root of the problem.