When you put an AC on to max setting, does the compressor pump actually move faster or does the airflow - the fan- just go faster?

And if it is just the fan, is there any reason to NOT have it on max AC all the time? Even in a car? Wouldn't that be more efficient?

the compressor only has one setting: on/off
the fan has 3 speeds: low/med/high
thats it

>>2926452
So why would anyone not have it on setting 3? You can just turn down the dial or manually turn it off when needed.

I think the compressor cycles on for less duty cycle if the fan doesn't warm the evaporator core as quickly.
The AC compressor in a car isn't always running, it very audibly cycles on and off.

>>2926453
Because you’ll be cold

>>2926468
That's for the thermometer to decide.

>>2926453
It's dependent on desired noise level, air movement, size of room, etc. The thermometer setting is for temperature control and by extension, cooling factor.

bump

Depends on the A/C. Inverter models can vary compressor speed depending on load. You typically can't control it though, just fan speed.

>>2926451
I'm guessing if the fan is on high it moves more warm air into the system which needs more energy to cool, which stresses the compressor more. The fan itself draws more energy and produces more heat on high as well.

>>2926449 (OP)
It is doubtful the compressor is not controlled by some sort of feedback. Control may be as crude as just switching it on and off with some hysteresis but it might be controlled by an inverter and linear controller.
I imagine a few things could go wrong if the compressor was just switched on. Those thermodynamic shit cycles aren't exactly known for being stable.

>>2926449 (OP)
I've investigated 4 of those portable ACs, tore them down for parts. 200-400 bucks range.
The compressors cannot be regulated, they're either on full power or off.
The only thing that's variable is fan speeds, the fan motors often have 2 windings for 2 different speeds which can be switched.
If the air moves faster over the radiators, you get a bit more cooling, but the difference is relatively minor.
If you program a temperature, these things will try to hold it by switching the compressor on and off.
Pretty much all of them have a timeout which prevent the compressor from switching on and off rapidly.
I suspect there's a starter winding in the compressor with a PTC that heats up and increases it's resistance to turn the starter winding off after a start, to prevent the starter winding from being fried since it would not survive continious operation. That's how fridge compressor motors work at least.
If the system is turned off, there's still higher pressure right at the compressor outlet, and the motor would need more torque to start against this pressure. If you let the system settle for a bit, the pressure will equalize and be much lower. The pressure differential can build up while the compressor runs since there is a capillary tube to constrict the flow between the hot and cold side obviously.

Take with a grain of salt, i'm not good with electronics lol.

>>2926453
Mostly noise, the most efficient fan speed is annoying sometimes. When I crank on the AC full in my truck I control the fan manually since it would go full speed until the cab temperature gets closer to the set temp..

>>2926449 (OP)
no, it just increases fan speed and cycles the compressor for longer run and shorter rest

>>2926517
thanks chatgpt

Going to sort of hijack this thread for a related question. I have a portable A/C and the spec sheet says it draws 12A. Its not clear if that's a max or what, many of the spec sheets seem to lack basic information.

Anyways I was running it just fine over the last couple of days, but today it blew a fuse. As far as I know, the A/C is absolutely the only thin on the circuit. The fuse that was blown is a 15A TD oldschool edison type fuse (I live in an ancient building). I did notice that the fuse gets very hot to the touch when running the A/C. My question - is the A/C responsible or could there be something else that caused this? When the fuse blew, the A/C had been running for like 15 minutes. Is it possible the A/C suddenly drew way more current than it should have and caused the fuse to go?

Assuming there are no other loads, what could cause this?

>>2926545

12A will be the maximum running current. It will likely draw far more than that for a brief instant every time the compressor turns on. Depending on the type of fuse, that could wear it out. It could also just be an out-of-spec fuse.

>>2926545

Older buildings using those style of fuses typically only have a few circuits per unit. I would take the opportunity while it is blown to identify all the recepticles and lights powered by it and move things to other circuits so it doesn't happen again.

Like others have said, it most likely is on-off compressor. All modern slightly not shit ACs have inverter compressors that can modulate from around 30-100%, as well as all modern heat pumps, but these small things will just be on-off.

As to keeping it on high fan setting, it is actually better to keep it on a high fan setting because it reduces the temp gradient for the compressor, and heat pumps (including small ACs) work better(in terms of power efficiency) the lower the temp gradient. The reason you'd run it on low is mostly noise, or if it's positioned such that blowing too hard is uncomfortable for people.
>>2926545
Assuming you're a burger, ~1500W is still quite a lot for a portable AC, but not impossible. If you're in 220V zone, then it definitely doesn't draw constant 12A. Your fuse might just have been shit. Buy a power meter, they're cheap and useful, then you'll know if it's the AC drawing too much.

>>2926453
Two reasons:

1 - Sometimes you might want it to run quieter. If you don't NEED it to run at max to get to the temperature you want, it's nicer if it doesn't make as much noise.

2 - Cooling the air too fast can cause the AC to pull less humidity out of the air. If the lower speed can reach the temp you want, it may feel more comfortable since the air will be dryer.

I used to live in a house that had a massive commercial AC unit that was WAY oversized (rated for an air volume like 3x the size of the building) because the guy got a good deal on the used equipment. This was very bad. The unit cooled the air so fast that the AC generated almost no condensation. The result being it was cold as shit, but it still felt hot and clammy because it was like 80% humidity inside, and everything inside would get cold and water would condensate on it. I would sit in a room that was 68 degrees, yet still be sweating because of the high humidity.

I had an HVAC guy come out and replace the AC unit with a much smaller one, now it cools the air slowly, and it is able to get the humidity out of the air. No more clammy bedsheets, no more sweating duct vents. And now I have the AC set to 74 instead of 68 and yet feel way more comfortable because the humidity is 40% instead of 80%.

>>2926661
The AC I have is a typical window unit but it's only for my small room. Definitely overkill.

All fags forgets that you can cut power and put it back. The compressor is not constantly on.

>>2926453
The noise.

>>2926453
higher air speed means the air will not be as cold. when the unit has a fixed compressor speed it delivers the same kw/btu of cooling all the time, when it has to cool down 3x as much air it can only do so by cooling it down 1/3 as much

>>2926449 (OP)
My AC unit works better when I set it to 68. The lowest is 66, but for some reason the cooling will keep cutting off when turned down all the way.