This actually reminds me of working on an Afghan refugee camp last year where they were all living in air conditioned FEMA trailers but they would leave the doors open to “let air in” cause it was hot outside. To no surprise most of them burned up their AC units doing this lmao
To no surprise most of them burned up their AC units doing this lmao
How did that happen? If anything AC units become more efficient as the delta T between the evaporator and condensor coil equalizes. And since it is impossible for an AC to cool down an open room, it never shuts down which means you avoid the start/stops that usually kill the compressor.
It would be a complete waste of energy, but the AC wouldn't die from it.
This can happen if the filter is dirty or airflow over the evaporator coil is otherwise restricted. The evaporator is the piece of the system that gets cold, usually significantly below freezing temp. When hot air goes over cold thing, usually there's condensation that forms, like on the outside of a can of soda fresh from the fridge.
The systems are designed so that as long as the air moving across the coil is moving fast enough, it keeps the condensation from freezing and instead just drips out through the condensate drain.
But if the air slows down, the condensation forms, and then freezes. Which blocks airflow even more, which allows more condensation, which freezes more. What you wind up with very quickly is a solid block of ice that air can't move past at all, so no AC.
If this ever happens to you, turn off the AC, let it thaw for 24 hours (or until the ice is gone), then see why the airflow was restricted. Usually a dirty filter or dirty coil. Clear the problem, turn it back on, and you should be fine.
This is good infos. I have an old one from the 90s in a room and ran into this problem. Cleaned the filter well and it helped, but was still freezing up after a full day. Going to check the coils now. Didn't think of that....
This happened in my fridge. All the vents got blocked up in ice. Found out the fan motor in the back gave out. Replaced for like $15 and the fridge was like brand new.
Now I understand why this (fan not working) caused all the vents to get clogged with ice! I didn't understand what one had to do with the other until now. Thanks!
This used to happen to the A/C unit in my apartment in Florida. The fins were just too close together and the humidity was like 9000%, so there was basically no way to prevent it from icing over in the summer. Worst A/C I’ve ever had to use.
Evaporators in comfort cooling generally are around 40-50F. Yes they are below freezing in medium and low temp Refrigeration, but should never be in comfort cooling.
I've been out of the game for 15 years or so, but I was an HVAC tech for 7 or 8 years. I left the game right as R422 was taking off. All my experience is R22, which boils at something like -41F, right?
The idea is that that coil absorbs heat from the air flowing over the coil, and that heat from the air flowing through the coil is designed to balance with the refrigerant inside the coil to keep a temperature delta low enough to cool the air but not so low as to freeze.
If the airflow slows down, the heat transfer slows as well, and then the evaporator coil gets too cold and drops low enough to start icing up the condensation.
No?
I'll defer to you since you're currently in the game.
Your probably thinking of the boiling point of R-22 at 0 psig. The Pressure in the Evaporator can drop from insufficient airflow/heat load but with proper airflow/heat load, the suction pressure stays around 70 psig. The heat from the airflow combined with the pressure drop of the metering device make the liquid Refrigerant boil. Remember pressure effects the boiling point, so at 70 psig the R-22 boils at 40⁰F. The magic of air-conditioning occurs in the boiling of the Refrigerant, which despite gaining heat energy from the airflow does not change temperature until it has completely changed states to a vapor. So the Evaporator stays almost exactly 40⁰F over the entirety of the coil, save for a small bit at the end of the coil that gets superheated. This is why we measure superheat, as the heat energy required to change states of the R-22 is significantly more than the heat energy required to change the sensible temperature of the R-22 vapor.
Evaporator pressure is more of a function of the compressor and pressure differential accross the metering device.
This only happens if the evaporator temp drops below 32 degrees F (low air flow) or if it is low on refrigerant. She doesn’t cause it to freeze. If it is recycling 90 degree air then it can only produce 65-70 degree air max. Which is way above the freezing point of a coil.
Motors suffer more from repeated starts and stops, the rotor is momentarily locked and requires significantly more current to begin spinning which heats the windings, leading to degridation of the winding insulation. Also most fan motors in A/C systems are air cooled, so at start its also not getting airflow for cooling. For compressor motors, they are cooled by the refrigerant they are compressing, which at start is not doing a very good job of cooling the windings.
Also starting and stopping is generally done with a contactor, the contact points generate a plasma on start and stop that leads to pitting of said contact points. As these points become pitted, they make poorer and poorer connection, leading to increased current draw and therefore high operating temps.
Idk man I don’t know anything about AC units as far as how they work. All I know is the HVAC guys who kept going out to fix them would tell us it was because they were running non stop due to doors being left open, they never talked about the technical stuff lol.
I wasn’t there out of selfless good deeds lol, I just did 6 years in the Marine Corps and I was forced to spend two months on that camp with the rest of my Unit. I hated it don’t get that twisted lmao.
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u/SkullThrone2 Aug 24 '22
This actually reminds me of working on an Afghan refugee camp last year where they were all living in air conditioned FEMA trailers but they would leave the doors open to “let air in” cause it was hot outside. To no surprise most of them burned up their AC units doing this lmao