Car A/C

[Nithin]

does it depend at all on how fast you have the fan going?

This is for a car that doesn't have temperature control. i.e doesn't maintain temp.

N.

 

[JSSheridan]

I'm not exactly sure where you are coming from, but I'll give it a shot.. The compressor only has one speed on my vehicle, and I'm pretty sure that I'd need to adjust the belts to change that. If you change the fan speed, that's not going to really affect how much power the compressor is drawing from the engine. It will only use a bit more power from the electric system.

Edit: I think that for my vehicle, if I turn the fan off, the compressor is switched off also.

 

[iwantanewcomputer]

^ agreed. the fan speed does not affect how much power the compressor is drawing. if the car has a temperature adjustment know (turn it from red to blue) or an actual temperature degrees setting that changes the compressor load.

 

[Mark R]

In most cars the compressor is driven by a belt connected to the engine, and therefore the compressor runs at the speed of the engine. When the engine runs faster the compressor runs faster and provides better cooling.

However, there is a thermostat that when the evaporator gets to a preset temperature (usually just above freezing), the compressor clutch disconnects it from the engine, so it takes no load. So, although the compressor takes more power from the engine when the engine runs faster, this is compensated for because it runs less often and for shorter periods of time.

The faster you have your fan set, the more air is pumped through the evaporator. With the fan speed set to high the evaporator will warm up rapidly when the compressor stops, so the compressor will run more frequently, and will run longer. On pretty much all systems, if you switch the fan off, the compressor will also switch off completely - otherwise you'll turn the evaporator into a block of ice.

However, the temperature adjustment (not electronic controls) doesn't affect the AC - it's totally seperate and works on the air after its been through the AC. If you turn it up to warm (red), all that happens is the cold air from your AC is heated up by the heater. The AC still sucks in the same warm air from outside whatever the temperature you have dialed in, so the compressor takes the same load.

Some new cars have an electrically powered AC compressor, the power of these units doesn't vary with engine speed (but when running, will load down the engine through the alternator).

 

[The Boston Dangler]

You can count on the AC in a car sapping roughly 10 HP off the engine. This most noticeable in small cars.

 

[harrkev]

A/C compressors also use magnetic clutches. The purpose of a compressor is to provide a pressure differential (by pumping freon). When the pressure differential reaches a certain level, the clutch disengages, so the compressor is turned off for a little bit.

On my 2000 Dodge Caravan (don't every buy one, by the way), the compressor will run for 5 seconds and shut off for 10 seconds.