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Sadly Gregg has passed away
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Discussion Starter #1
Is it helpful mechanically to turn off the AC before stopping the engine? What about letting the engine function on startup for a minute or two before turning on the AC?

This issue is quite controversial with my coffee clatch....seems most of us just leave the AC on full time in trucks and tractors.
 

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I've always understood AC to drain the battery and power whilst driving so only use mine whilst cruising on a hot day. OK, so living in the UK we use the hot air blowers for 363 days and the AC for only 2 days of the year so it's maybe not so noticeable for us - unfortunately :(

In previous cars I've noticed a drain on engine power whilst using the AC on a hot day as well as an increase in fuel consumption.
 

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Premium Member 1999 SLK230-sold
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I guess been in Phoenix that A/c runs good 9 month out of the year. I have switch the A/c on after the motor runs for a moment. Also i switch the A/c off before i shut the engine off. I guess it is just a habbit of mine. If i leave the A/c on while starting the engine i get a puff of hot air before it blows cold.
 

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Sadly Woolly has passed away
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It's more economical in the long term to keep the AC running all the time - which is why MB have designed it that way on the R171 - you have to make a conscious effort to turn it off, and even then, it will default to 'on' at the next restart. As to 'draining the battery' - if you get battery drain whilst the engine is running, then you need a new alternator/AVR.
 

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Premium Member 2013 SLK250
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I do believe in the start mode all power to most everything is auto turned off except the start motor and the engine stuff needed for it to run and safe stuff until the engine starts anyway. AC, radio and etc will be in an off mode.
 

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Sadly Woolly has passed away
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I do believe in the start mode all power to most everything is auto turned off except the start motor and the engine stuff needed for it to run and safe stuff until the engine starts anyway. AC, radio and etc will be in an off mode.
Correct, whilst the engine is starting, but once it's up & running, a lot of systems are turned on automatically by default, including (on the R171) the AC.
 

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Not turning the AC on for long periods of time also tends to dry up the sealing rings causing leaks in the system. On my automatic climate control sedan, the AC/climate control is always left on. On the SLK I tend to leave the AC on. No battery issues on the sedan - jury still out on the SLK.

Len
 
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Sadly Gregg has passed away
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Discussion Starter #9
Correct, whilst the engine is starting, but once it's up & running, a lot of systems are turned on automatically by default, including (on the R171) the AC.
So Woolly....are you saying that in the R171 the AC compressor is always in the "on" mode even when the small red light on the switch is inactive?

On my big Ford truck the AC runs constantly in every mode including defrost but does not run in the basic heat mode. Kind of weird to me that it runs in the dead of winter, but I suppose it aids in defrosting and controlling the temp of the hot air!
 

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Sadly Woolly has passed away
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So Woolly....are you saying that in the R171 the AC compressor is always in the "on" mode even when the small red light on the switch is inactive?
Yup, bizarrely (?), the red light is only on, when the AC is off. Whilst it is running, the seals carry on sealing, and the compressor caries on compressing - it's only if you physically turn it off every time you drive it (and the red light comes on) that you might start getting problems. As well as cooling the air when it's hot outside, the AC dehumidifies the inside air when it's cold outside - stops the windows steaming up.
 

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Yup, bizarrely (?), the red light is only on, when the AC is off. Whilst it is running, the seals carry on sealing, and the compressor caries on compressing - it's only if you physically turn it off every time you drive it (and the red light comes on) that you might start getting problems. As well as cooling the air when it's hot outside, the AC dehumidifies the inside air when it's cold outside - stops the windows steaming up.
Yep thats definitly the way it works, I have had many problems with mine and check it regularly.
If the RED LED is on the A/C is OFF. You can easily prove the A/C is off just by lifting the Hood and touching the AC pipe, it's alloy and gets super cold and covered in condensate when AC is active.
I can hardly tell by engine noise/load if AC is on or off as is often common on many cars. SLK350
 

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Premium Member 2006 SLK350
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Most modern cars use the A/C to defrost when it's hot outside - ie. if you have the temp control to cold, and you select defrost, it engages the A/C which pumps cold, but dry, air to the windscreen. You'll notice that you'll often get condensation on the outside of the window.
On the SLK when you select defrost you get 1000 degree C air regardless!
 

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Founding Member #2 2008 SLK55 AMG
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IIRC, the airconditioning button is different in earlier model year R171. As Woolly stated it is default to on (the control button will be labeled A/C OFF, so if the red LED is on, it means A/C is off) in earlier models.

Later models (R171) show only A/C. In this case a lit red LED means A/C is on, and when the LED is unlit, the A/C is off. This is on my 2008 R171.
 

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Premium Member 2006 SLK350
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Stirring the pot...

06 SLK 350, originally US.

The AC switch is default OFF, including if you run the temperature down below 16C (60F) which causes the cabin fans to run MAX even in AUTO. However, if you cycle the AUTO switch, it will make the AC come on. That said, AC on has a red led, AC off is light out.
 

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Not turning the AC on for long periods of time also tends to dry up the sealing rings causing leaks in the system. On my automatic climate control sedan, the AC/climate control is always left on. On the SLK I tend to leave the AC on. No battery issues on the sedan - jury still out on the SLK.

Len
Bingo! This is why they make them come on either all the time, or first on the switch. (so the a/c turns on before you get to the heater). There is one more problem with leaving them off for longer periods of time.. the refrigerant will condense and then when you turn on the system, it tries to pump a liquid instead of a gas.. thus blowing out the seals.
 

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After reading a number of articles on this subject, I've come to some conclusions that seem to make sense.
#1. I always turn the AC compressor off a mile or so before shutting the car off, and turn the blower fan to high. This blows most of the accumulated condensation out of of the evaporator and prevents that stinky smell when you drive it the next time.
#2 I usually drive a mile or so before turning the AC compressor on, whether just leaving the house or when running errands. After the car has been driven for a couple of minutes, there is ambient air flow through the AC condensor and through the engine compartment which eases the AC system start up as the high & low pressures in the system tend to equalize.

I also turn the compressor on when the engine is at idle. Again, this is easier on the compressor, the compressor clutch, and the drive belt.

I've driven a couple of vehicles in excess of 250K miles doing this & not had any AC problems, . . . .so maybe it works!!
 

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Sadly Gregg has passed away
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Discussion Starter #17
IIRC, the airconditioning button is different in earlier model year R171. As Woolly stated it is default to on (the control button will be labeled A/C OFF, so if the red LED is on, it means A/C is off) in earlier models.

Later models (R171) show only A/C. In this case a lit red LED means A/C is on, and when the LED is unlit, the A/C is off. This is on my 2008 R171.
Yep! Just like Eddy says......Challenge's AC is on when the red indicator is illuminated. Weird to me that in earlier models no light means AC on.....that is not standard design protocol for US gadgetry.

Don't think Woolly and the others would have been "gaslighting' me, but I am easily confused since reaching the advanced age of 55! However, ahhhh......I forgot! :biglaugh:
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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55? rookie!
 

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Just to add this from my "Operator's Manual SLK-Class" on A/C;
Deactivating
It is possible to deactivate the a/c(cooling) function of the climate control sys. The air in the vehicle will then no longer be cooled or dehumidified.
> Press button [A/C rest]
The indicator lamp on the button goes out. the cooling function switched off after a short delay.

Just as Der Flieger stated :tu:
 
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