Why car engine lags when AC is switched ON?

Discussion in 'General Electronics Chat' started by Lanz, Jan 7, 2010.

Do you found the same situation?

  1. Yes

    80.0%
  2. No

    20.0%
  1. Lanz

    Thread Starter Active Member

    Oct 30, 2008
    153
    0
    My car engine lags when i switch ON the AC.The RPM drop a bit.My car was quite old but i found the same situation in modern cars also.Except on modern cars,the RPM will be adjusted to normal by ECU.I know that when i switch ON the AC,the clutch at the compressor works.But i wonder whats the relationship with the engine lagging?Does the compressor drains a lot of current from the battery?
     
  2. Paulo540

    Member

    Nov 23, 2009
    188
    0
    the mechanical load from the compressor imposes a drag on the engine through the pully system.
     
  3. Lanz

    Thread Starter Active Member

    Oct 30, 2008
    153
    0
    Any solution to solve this problem?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You'll always see a decrease in performance and fuel economy when you engage the A/C compressor. As Paulo540 noted, it increases the drag on the engine. Some systems increase the power output to compensate, older systems do not.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Yes.

    Turn off the A/C, roll down the windows.
     
  6. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    If it is a problem, you should take your car to a service station. Your AC is driven by belt drive. It will not drain much battery power. But the energy needed to drive the compressor is taken from the engine, hence the increased load on the motor.
     
  7. Lanz

    Thread Starter Active Member

    Oct 30, 2008
    153
    0
    Yup,i noticed that.

    Yes,i always do that [​IMG]
    And my ear cnt bare with the wind sound came from outside when the windows are rolled down especially during long driving.
    How when its raining?
    If you nvr ON your AC,then the windshield will be covered with condensed vapor.
     
  8. thyristor

    Active Member

    Dec 27, 2009
    94
    0
    I have twin alternators on my diesel-engined boat which are electronically controlled to kick in a couple of minutes after starting to allow the engine to warm a little first.

    They will deliver 100A initially at say 14v so that's 2HP. However, alternators are only about 50% efficient so the load on the engine is actually 4HP. One definitely hears the change in engine note as they activate.
     
  9. Darren Holdstock

    Active Member

    Feb 10, 2009
    262
    11
    This is more of an issue with smaller engines. Air con compressors don't take so much of a bite out of bigger engines as the extra load is relatively insignificant compared to the normal load imposed from lifting the valves and piston compression of the fuel/air mix.
     
  10. bluebrakes

    Active Member

    Oct 17, 2009
    245
    7
    air con is driven via belt directly from engine. An electronic clutch engages the AC when button is pressed.

    The compressor has to compress tetra floura ethane (modern alternative) gas. typically 220PSI on high side.

    On a small engine with not much engine torque, the lack in performance is very noticable.

    I've got an Audi 2.7 V6 S4. Unless your ragging it, you don't really notice any difference at all. Only fuel consumption.

    Air con shouldn't affect battery voltage at all. It may require a few amps for the clutch but that's it.
     
  11. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    Somewhat wrong then using AC you must have the blower on. And the blower draw more current than the clutch. But anyway in a car with a functioning electrical system this should not be problem. As the car generator will generate the needed energy.
     
  12. Lanz

    Thread Starter Active Member

    Oct 30, 2008
    153
    0
    Yes,its true.
     
  13. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The tiny car barely has enough power with the air conditioning turned off to move because its engine is only 1.1l like a North American lawn mower.
    When the air conditioning is turned on then you know what happens.
     
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