I have noticed that when my ac is on, the engine will shudder while sitting at idle or moving very slowly as if it had a misfire or sudden loss of power. It does it regularly at about every 20-30 seconds. At first I thought this was the "bad gas" excuse the stealership gives to people but I only ever use premium gas and this also only happens with the AC on. Now that it is cooler out, I stopped needing the ac, and it magically does not occur anymore. I get no engine codes for this either. Anyone have any suggestions as to the culprit?

 

When my air is on I get a similar effect , I just wrote it off to being a big drag of power, after all it is just a 1.6l motor and when I turn it off its gone.

 

I figured this as well, but I would think there must be something wrong. Otherwise this has to go down as worst power management system ever designed.

 

Yep, in my Non-S Cooper I never use the AC unless my girlfriend is in the car

Just drains a big chunk of power that we can't afford to spare. You wouldn't notice it on a big V8, but as ACallahan stated, it's just a little 1.6L so you do feel it.

 

AC does load the engine, but it shouldn't be that much. I don't notice the drag on the engine when I run the AC in hot weather. You notice when you calculate your gas mileage, but not in everyday driving. The 20-30 second interval makes sense -- your AC is cycling on and it loads the engine. My first guess is a bad bearing, or bad AC compressor pump.

I'd be observing the AC compressor with the hood up to see if it squeals or growls or something when it cycles on. Maybe listen with a stethoscope. And read the chapter in AC in the manual. Or just find a local shop with a good rep for AC repairs, if you don't trust the dealer.

 

Mine starts squealing when I turn it on
Something wrong?

 

Most likely the low stage of the cooling fan is bad, when it gets that sudden surge of power to turn the high fan on. Feels horrible in cvt vehicle when it happens coming to a stop sign.

 

That is def possible. My AC works fine, and usually right after it studders I can hear the fan going on high. So then does the fan need replacing or do most ppl just deal with it? I have a manual and it can still sound bad...to the point that I expect the engine to die.

 

You should replace it, maximize your cooling potential, While it is not life or death for your car if the high side should fail(extremely rare but possible) then you would almost certinally over heat then the real expensive stuff starts breaking

 

What does the cooling fan have to do with the AC? The engine cooling fans are electric, not belt driven and wouldn't sap the engine power. That said I can have a stumble on cold start up with the AC on and occasionally when stopped, never a stall but idle rpm might dip to 600ish then rev back to 8-9ish. I've always noticed the difference since day one with the A/C on or off, it's definitely a drag on the powertrain, a noticeable one. I'd say is about equivalent to the difference in power from a 90 degree or 50 degree ambient temperature on the butt dyno.

 

when ac is turned on low cooling fan is auto turned on to maintain proper pressure in a/c system, with out the cooling action of the fan heat builds up as does the pressure, when the low stage fails the high cycles on and off based on the increased pressures. this inturn creates a large amperage draw at once with increases the load on the alt. which bogs the engine down