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Aircon clutch or something else?

Suberman on Tue May 11, 2010 9:41 PM User is offline

Year: 2007
Make: Subaru
Model: Impreza STI Spec C
Engine Size: 1994
Refrigerant Type: R134a
Country of Origin: Japan

So i realised 2 days ago that after i shut off the engine, the aircon (i don't know what you call that) armature or clutch wheel :confused: is still spinning even when the aircon clutch or engine is totally off.

See this to get an idea of what i mean. Aircon problem

Notice at about 0:42-43, the wheel spins backwards a little? Mine spins backwards quite a number of turns before coming to a stop.

So i sent it back to the dealership, they did a gas recharge and refill and tightened the belt. It still does it, but to a lesser extend. It now spins back about 1/4 to 1/2 of a turn or so.

Shouldn't it stop completely once the aircon clutch disengages? Like the video? Seems like this is caused by the gas flowing backwards or something like that.

My car is almost new with only about 1,000 miles, but has been sitting in storage for over 2 years. Is this of any concern?

Edited: Wed May 12, 2010 at 4:37 AM by Suberman

HECAT on Wed May 12, 2010 8:33 AM User is offline

It's normal. When the compressor is engaged it generates a pressure differential between the discharge (high side pressure) and intake (low side pressure). When disengaged, this pressure differential can turn the compressor backward a little as the pressures equalize.

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FLUSHING TECHNICAL PAPER vs2.pdf 

Suberman on Wed May 12, 2010 11:47 AM User is offline

Thanks Hecat. But in my case, the wheel or whatever that is called rotates back quite a number of turns. The one shown in the youtube link shows it rotating back like 1/10th of a turn or something like that. What could cause it to rotate back that much? Perhaps something is not regulating the pressure?

The dealership evacuated and recharged the gas and now it turns 1/4 to 1/2 of a turns (which is alot better than before) but still more so than my other Impreza that doesn't happen to do it.

I'm concerned if the 2 years of storage has something to do with it. I mean it has only done 1,000 miles.

I hope to be able to pinpoint it and get the dealership to fix it before my warranty expires.

HECAT on Wed May 12, 2010 12:10 PM User is offline

With a loose belt it was easier to back up the compressor (a few turns) than to equalize pressure through the TXV orifice. Now the belt is tighter (the dealership did fix it), it will hold against more pressure, turn less, and now forces more pressure to equalize through the TXV.

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HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

Suberman on Wed May 12, 2010 1:30 PM User is offline

So how do i equalize the TXV? The tightening of the belt sounds like a band-aid? Or am i wrong? What is TXV anyway?

HECAT on Wed May 12, 2010 3:37 PM User is offline

Thermal Expansion Valve (TXV)

The pressure equalizes on its own when the system is turned off; there is nothing for you to do.

Your concern is regarding something that is not abnormal.

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HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

Suberman on Thu May 13, 2010 1:45 PM User is offline

Thanks for all the help Hecat! I guess it isn't much wrong with it then, but for my understanding, since its a pressure related issue, would the amount of gas affect this spinning back issue?

HECAT on Thu May 13, 2010 2:21 PM User is offline

No, but it would not do it if there was none in there.

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HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

Suberman on Thu May 13, 2010 9:19 PM User is offline

Sorry to be asking so many questions, I just wanna make sure that if there is anything i could do, i'd push the dealership to have it replaced/rectified under warranty.

One last question: What is (could be) the reason for if this particular compressor does it more than another?

Thanks for your time Hecat! Appreciate it!

HECAT on Fri May 14, 2010 6:02 AM User is offline

No two will be exactly the same because there are too many variables; internal pressures vary (ambient temp, heat load, heat removal, and more), combined with external force as already seen (belt quality and tension), and the internal design of the compressor (the particular stroke position at shutdown).

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HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

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