Hello! Would appreciate any basic explanation on how airconditioners work. Mine just got busted (and I’m from a very hot, tropical country!). I’m tempted to just call the maintenance guy, but I thought it would be a good opportunity to first learn about it before spending some dough. I’ll be using A/C units all my life anyway.
Been watching some YT videos but once terms like “latent heat vaporization” are mentioned, my mind just shuts off. Many thanks to all the articulate and patient folks out there!
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The main idea of all ACs is the same.
If you have a gas and you pressurize it, it gets hot. You can try it: if you pump a bike, the pump gets hot at around the valve. (When I was child, we had metal valves that literally burnt our fingers.)
If you release a pressurized gas, the opposite happens: it gets cold. You can try it if you have a CO2 cartridge (like this home made soda machine). When you pop it open, it gets frozen cold.
An AC unit has two sides, a cold and a hot side.
The hot side is outside of the apartment and it has a pressurized gas tank and a pump that keeps the gas under pressure. This gas is the working thing that is the heart of the whole unit.
The cold side is in the apartment, and it’s basically a lot of tubes. When some cooling is needed, a valve releases some gas from the hot side into the cool side. The gas expands into the tubes and cools them down.
Then a simple fan blows air through the cold tubes and you have your cooled air.
Then the same gas is pressurized again and circulates in the closed system.
Of course a real AC unit has a lot more things: electronics, filters and so on. Any of these can go wrong/clogged.
So you know how when you spray deodorant the can gets cold and the spray itself is cold? That’s because you’re taking a gas that’s stored at a higher pressure and releasing the pressure when you spray it.
An air conditioner unit has two sides:
A compressor side where the gas in the system is compressed. Compressing the gas creates heat, which is cooled by a heat exchanger outside (basically a radiator with a fan) so your room doesn’t get hotter.
On the other side is where the gas pressure is released, just like the gas from your deodorant can but within a sealed system) and the cold gas is fed through another heat exchanger to distribute the cold air to the room. The gas itself stays in the system but by cooling another radiator the air around it is cooled and this cool air is blown around the room.
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Good answers here, let me relate what I remember from physics class.
Think about basic water. It can be solid, liquid, or gas. The difference is the TEMPERATURE. It needs additional energy to move to a more “excited” state, and removing energy makes the molecules “less excited”. Add heat to liquid water and it will change states into steam. Remove heat from liquid water and it changes to ice.
So we know we can control the liquid/gas state by adding or removing energy. An AC unit uses this concept and reverses it. It’s a closed system where pressure can be controlled. It uses pressure – that’s the compressor unit – to force the gas coolant back into a liquid state. That action forces it to release energy. The heat goes out through the heat sinks, and a fan blows it out from underneath your fridge.
Now you have cold, liquid coolant. That gets pumped through pipes to cool the air around it. The coolant steals heat from inside your fridge. The coolant is pumped slowly enough that it has room in the pipes to expand back into gas. It absorbs energy to make that transition. Once it’s turned back into gas, it completes the loop and goes back into the compressor.
As for repairs on an AC unit – I’m no expert, but a few things can go wrong. The motor could be bad. The capacitor used for starting the motor could be bad. There could be a leak and a lack of coolant, in which case the unit may run but the air won’t be cold. What happens when you try to start the AC?
AC has thin little metal fins on the front that get really cold and a fan that sucks the room’s air into the fins.
The hot room air passes threw the fins and turns cold, this air is thrown back into the room.
Since the only way to make air cold is to remove heat from it, you transfer this heat to the outside part of the AC. It has the same little metal fins on the other side of the AC. These fins now have the heat from the inside air. A fan blasts outdoor air threw the fins, which cools the outside fins off. Now the heat from inside has been released!
Do this over and over, little by little and you are left with only cold air. Which is just air that has had heat removed from it.
Evaporation of liquid to gas uses heat (temperature drops). The flip side is that when you condense gas to liquid, it gives off heat. This only really works when volume is constant and pressure change is the reason for the heating or cooling. Special gases (chemicals) are used as coolant that evaporate and condense pretty well in the range needed, and take or give a lot of heat in the process. Not any old chemical will do the job.
So, heat exchange systems like a fridge or air-con has a closed system that passes inside the area to be cooled, where pressure is low and the liquid evaporates, cooling things. The gas is then passed outside the area to be cooled, where it is compressed, heating it up. The heat is moved from INSIDE to the outside.
If you blow air over the cold zone (coiled tubes, usually), it will cool the area it is in fairly quickly. Outside, though, it is heating things up. Normally, “outside” is literally, physically, out on the wide open atmosphere, so the heat is tiny compared to the amount of air, and unless you stand right next to the fan of the AC/fridge, you don’t notice it.
A fridge in a house, or big fridges in stores or factories or whatever, can put out enough heat to affect room temperature. Usually don’t because fridges don’t need to run a lot, but if you keep opening the fridge or air is leaking in and out of it so the fridge runs a lot, you might actually heat up the room quite a bit, and notice it. Industrial and large commercial systems tend to push that air to the outside to avoid this possible problem.
Now, if the coolant (the liquid/gas used to move heat by evaporation/condensation) runs out (maybe a small leak in a coil or something, blown gasket on a compressor that pressurizes the gas), then the system won’t work.
Most failures to coolant systems are either due to loss of coolant fluid, or failure of the compressor.
Pretty good answers as far as how AC work. But do not try to fix them on your own. It’s not a do it yourself area beyond cleaning filters, condensation lines
It’s a two step process: Compression and expansion of gas.
An air conditioner does not ‘cool’ air. It removes the heat from it.
When you compress a gas, it absorbs heat.
When you expand a gas, it releases heat.
So, the basics of the air-conditioner is to absorb the heat from the air in the house (return air) by compressing gas. This hot gas is then pumped outside the house where expansion releases the heat outside, cooling the gas again. The cool gas then returns to the house and is pump through an evaporator which is basically a fan blowing across coils containing the cold gas.
The air blowing across the coils transfers heat from the air to the gas. The resulting air feels cooler, and the gas is pumped outside again.
It just keeps looping around.
The main thing at play is that when a liquid turns into a gas, it gets colder, and when a gas is compressed into a liquid, it gets hotter. The liquid can be anything, but we use special liquids that are more efficient and can handle more extreme temperatures than plain water, and generically these liquids are just called ‘refrigerants’.
Your AC system is a closed loop, meaning it’s just a pipe where both ends are connected to each other, and the refrigerant is on the inside of the pipe. For your house, half of the loop is on the inside of your house, and half of it is on the outside of your house. Using a compressor, the refrigerant is condensed into a liquid as it goes outside your house and gets hot. We use a big fan outside to blow air across the pipe to help cool it down, and as it renters your house, it loses pressure and starts turning back into a gas, causing it to get colder. On the inside of the house we use another big fan to blow air across the cold pipes, this makes the air cold, and using duct work send that cold air to various parts of the house.
A common misconception is that when you turn a thermostat to a certain temperature, let’s say 72F, that your AC is blowing out air that is 72F. This is not how air conditioning works, the cold pipes are very cold, and the air going past them are very cold. When your AC is on, you are pumping very cold air into your house and it is mixing with the warm air that is already there. When the mixture reaches the temperature that is set on your thermostat, it stops until it needs to add more cold air into your house.
Air conditioners contain a special fluid and a mechanism that can force said fluid to change between a liquid and a gas. When the liquid turns into a gas, it absorbs heat. When it’s compressed back into a liquid, it releases the heat. In a way, this fluid works like a sponge, but for heat.
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