A/C Compressors

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Dec 6, 2014
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Minnesota
Does anyone know why in newer cars you don't feel a power loss when the a/c kicks on but older cars you do? In my 05 accord I can definitely feel a power loss but in my 08 and 10 Civic I feel nothing. Is it that newer compressors are more efficient or does the electronic throttle compensate for it?
 
Depends on the make & model, 4 cylinder Accord vs V6. Newer vehicles have more efficient AC compressors but many vehicles will turn off the AC compressor under high throttle demand like flooring it to pass a vehicle.
 
Many new cars use a variable displacement compressor. Only pumps as much as needed instead of full throttle all the time. Others are clutchless and always on so you wont feel it or hear the clutch click.
 
Originally Posted by Chris142
Many new cars use a variable displacement compressor. Only pumps as much as needed instead of full throttle all the time. Others are clutchless and always on so you wont feel it or hear the clutch click.


I think newer VW's are always on.
 
You feel it in my truck, especially when the engine fan kicks on 100 percent and my truck has 350hp and 650 ft lbs of torque.
 
Originally Posted by Chris142
Many new cars use a variable displacement compressor. Only pumps as much as needed instead of full throttle all the time. Others are clutchless and always on so you wont feel it or hear the clutch click.


This is the best answer.
 
the a/c in my car is electric... keeps running even when the engine shuts off at a light, etc...

but then again, so is the water pump, power steering, etc...no accessory belt drive at all.
 
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I'm not sure about your Honda's since they use a traditional compressor with a clutch. The compressor in my wife's VW is variable so you never feel it kick on/off.
 
Originally Posted by motor_oil_madman
You feel it in my truck, especially when the engine fan kicks on 100 percent and my truck has 350hp and 650 ft lbs of torque.

Odd. Does not effect the 158hp idi in my f250. At least I can't feel it.
 
No offence but if the old 7.3 IDI is already slow as a snail are you really going to notice if it's a tad bit slower?
 
People get used to it any never notice the drop these days, especially if they use auto climate control.

A lot of this come from memories of old AC systems in cars. Those compressors were huge and the power hit was noticeable. It's a lot more efficient today.
 
It's possible that vehicles with DBW throttle open the throttle a little to make up for compressor drag when cruising as well as at idle..
 
Originally Posted by Chris142
Originally Posted by motor_oil_madman
You feel it in my truck, especially when the engine fan kicks on 100 percent and my truck has 350hp and 650 ft lbs of torque.

Odd. Does not effect the 158hp idi in my f250. At least I can't feel it.


Lets realize that the nameplate rating, and what the engine is actually producing at a point in time, are different.

Some is related to rotational inertia, some of it is related to how hard/fast the compressor engages.

I wouldnt doubt that there is some unloader valve in some of these, similar to newer easy to start OPE, to help it come on.

Quality and design of compressor, and number of cylinders or other compressor design surely makes a difference too.
 
The post above gets it right. The electronic tuning is designed to make it not noticeable, and to disable the compressor at higher loads. Plenty of today's vehicles use a conventional compressor, that eats up the same amount of HP as always.
 
The old clunky way there was a solenoid that bumped the throttle when the AC clutch hit and was supposed to nullify the event. New vehicles with DI and fly by wire throttle have completely tuned over it so you don't feel it. Nonetheless the load is there and more air/fuel is needed when it occurs.
 
Not just drive-by-wire, but for the past three decades we've had idle air compensators (or idle control motors) on throttle bodies that accomplished the same thing.
 
On the Mazda SkyActiv 2.5, the regular idle is 550rpm but it bumps up to about 750rpm when the AC kicks on. I don't feel it or even hear it. I only see the tachometer move.
 
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