I had a question about running the A/C

(i have the standard, 07 manual A/C)
Does adjusting the temperature change the load the A/C compressor puts on the engine? I hate driving with the A/C on because it really takes some power away and makes the RPMs drop a lot faster and takes a lot more effort to raise them for downshifting...if I were to lower the cold temp from the highest to say a notch or 2 from the lowest cold (close to neutral) would that make the compressor put a lighter load on the engine (making rpms not drop as fast)? or does it run the same all the time and the temp control on varies the air flow?

Thank you

 

Having the air on shouldn't make THAT much of a difference in your power. These are new cars... not like my 68 Mustang that did hesitate if the air was on.

I would imagine that the power draw is the same regardless of what temp you have it set at-- but I could be wrong.

 

Really? lol

Try a 400 RPM dip maintaining a steady 3000 RPM's with no load, and 10-15 HP.

 

I think the compressor is either on or off. The colder you have your temperature/thermostat set, the more often it will stay on.

The answer you're looking for is that when it's on, it's on full-blast; and when it's off, it's completely off.

 

If the compressor is running it's running, when you go to full power or it senses it doesn't need to be running to maintain the set temperature it engages the clutch (Slipping it so it's not zapping power anymore).

To my knowledge there isn't any variable slip, it's either running or not running.

 

The way the thing was explained to me was: if the blue snowflake light is on the compressor is on, even if the unit's blowing heat. The system first cools/filters the air then adjusts the temperature blowing through the car to the setting. If you don't want the compressor to run turn off the snowflake.

 

Changing the temp setting changes the amount of time the compressor is running. Others are correct, the compressor is either on or off. At the coldest setting it is running a lot (maybe all the time depending on the outside temp). As you set the temp wheel warmer the compressor is engaged less often. Unless it is brutally hot outside I typically set mine a couple of notches warmer than the coldest setting. This still keeps the car cool but the compressor runs less. I also had my windows tinted, that helps A LOT.

 

Yeah it seriously is rediculous how much more effort it takes to rev the engine...and how quickly those rpms are lost...most of the time I never run the AC (tho it is catching up now that its summer and I'm here in Florida)...normally what I will do if I do need the AC is leave it on full and will circulated air (stays colder faster) when cruising...When I come up to lights I turn it off (usually for good in stop and go) and leave it on circulated till that air gets hot or stuffy...usually by that time I am at a cruising speed and can switch the AC back on

Basically I try and only have it on when I'm not in need of shifting (cruising speed) because it annoys me how much performance is lost...plus it forces a higher idle...without AC it sits nice and happy at 500...AC does about 800

It is crazy...the other day I was cruising at 43 in 4th with the AC on full blast and was averaging 47mpg!!! that was a little crazy and I think it was a software glitch at the time (will see today) but normally at those exact settings I can push 43 mpg...I do have the non S tho

Oh yeah the tint is amazing...It's crazy how much sun and heat it blocks

 

Slightly off topic....but what % tint do you have and do you have any pics?

 

I haven't seen a drop in RPM on the 08 R55.
The engine is the same as the 08 R56. It's a tough bugger.

 

Its 2 0 % and yes here are some pics...personally I think it is the best percentage, dark enough for this FL sun, and easy to see outside at night

 

Yeah but when I first got the car, and become accustomed to it, it was winter, so I was used to just the raw power. Now that it is really heating up, just the drag this compressor puts on the engine is extremely noticable...If you have a stick shift, drive it hard and light for a while without the AC, then try it on...have the radio off and just feel the car...you can feel the power it drains, which yes isnt crazy, but boy does it bug me haha

 

Mine is 50%, the darkest VA law allows. Pic looks a little darker than it really is.

 

The RPM's won't drop at idle. Hold the car at 3000 RPM's in neutral and hit the AC. Watch and weep...

 

The belt is always turning the AC compressor pulley. The compressor has a clutch that engages the compressor when cooling is called for. Obviously when the clutch is engaged, the drag on the engine is greater.

The AC compressor is either on or off. There is no temperature setting for the coils. When the driver sets the temperature on the controls, the blower just blows cold air until the internal temperature reaches the set point, then it turns the blower fan down. That's why it doesn't cool the car down any quicker to adjust the temperature lower, that would just make the blower run for a longer time.

On modern cars the AC compressor is designed to automatically go offline at WOT. So no need to manually turn it off when flooring it.

 

My cooper s with the AC on feels as anemic as every other 4 cylinder with the AC running. I avoid the AC like the plague as it clobbers engine power. I'm used to BMW's inline 6s and the AC never made a difference.

It bugs me more that the HVAC blows hot air if I turn on the vents without AC - even when it's 50 degrees outside.

 

I have noticed at times the car is completely different to drive with the AC on. The power is way more abrupt and it seems really difficult to drive the car in a smooth manner. Much like a 2 stroke engine where the power is building building and then BANG extreme surge. This lead me to think that the AC was much like the Power steering as it does not rob the engine of power, maybe the engine compensated for the loss.
I killed that theory by turning the AC on and off while maintaining 2nd gear and you definetly feel the pump turn on, feels like a wall of wind resistance has hit the car.
ALSO For what its worth, at extreme AUTOBAHN speeds (135 mph and higher) with the "sport button" turned on if you turn it off, you feel the same LET DOWN, you feel the car actually loose substantial pull all while maintaining same speed. I added this FYI simply because I have noticed some people say the sport button does not have any effect on power.

 

The Owner's Manual for my 07 says this, "When the cooling function is on, the air is cooled, dried, then reheated according to the temperature setting. The recirculated-air mode may be switched on automatically."

This seems to indicate the compressor always runs the same, cooling the air to the "max" and then the car mixes hot air from the heater with it to achieve the desired temperature setting.

My old 86 911 does what you are asking. When you turn down the temp setting, it puts less load on the compressor. That would be a nice feature in the Mini IMO.