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A/C not cooling and causes RPM's to jump

 
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  #1 (permalink)  
Old 19 Jun 2009, 11:51 am
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Join Date: Jun 2009
Location: Walnut, Ca
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Post A/C not cooling and causes RPM's to jump

I should probably start off by giving the specifics of my car: I've got a 2007 PT Touring Edition with just over 37K miles. I've been having this problem with my a/c for about two months now, but it's not a consistent problem(which has created a problem of its own when trying to take it to the dealership for a diagnosis).


I would say 6 or 7 out of 10 times when I turn on my a/c, it will begin to cool down, but then it suddenly causes my RPM meter to jump slightly, then dip low enough that my car almost feels like it's going to stall(this results in a 'lunging' and 'settling' feeling, as if it's switching between gears). This usually happens when I'm at a stop sign or in park. A mechanic at my workplace took a quick look at it and said that it seemed as if the compressor was going out, causing the RPM jump because it was engaging and disengaging.


The weird thing is, sometimes I won't have this problem at all. And sometimes I can warm the car up and drive for a while, try the a/c again, and it will work.


I took it in to the dealership about a month ago and they found that the system was low on refrigerant. They charged the system and tested it with leak detector but found no evidence of a leak. The same day they gave it back to me, I knew the problem hadn't been fixed. I took it back in just yesterday, now they're calling me to come and pick it up but saying that they didn't find the problem because it didn't act up while they had it.


Any information or suggestions that you can give me regarding this problem would be greatly appreciated.
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Old 19 Jun 2009, 12:09 pm
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Join Date: Jun 2009
Posts: 80
Default Re: A/C not cooling and causes RPM's to jump

Your first mechanic is absolutely correct. The compressor is going out and is dragging the engine down. I know this because my 04 Limited is currently doing this exact same scenario. Sometimes it would do it, sometimes it wouldn't.

I simply don't run the A/C or Defrost right now until I can get it fixed as the compressor is fairly expensive just for the compressor itself (about $500). If you can afford to have the compressor replaced, do it. Otherwise, as long as you don't run the A/C or Defrost at all you shouldn't notice it as the compressor will not be turned on and will be free wheeling.

If it starts doing it without the A/C or defrost on and running, then the compressor bearings have gone completely and it's time to replace it no matter what as it will drag the engine down pretty bad until it seizes completely and burns up that belt.

Sounds like your first mechanic has a good head on his shoulders, see if he can recommend a good shop that will do the job and take it there for a check and pricing, making sure to tell them that the compressor seems to be "Bogging" the engine down when it's running, and not blowing as cold as normal.

Merely my 2 copper.
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Old 19 Jun 2009, 12:09 pm
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Join Date: Dec 2003
Location: San Antonio, Texas
Posts: 535
Default Re: A/C not cooling and causes RPM's to jump

Your cooling fan is not working properly. It causes the head pressure to get high and the high pressure valve vents causing low freon. Your fan is not working on the high speed side. Seen it more times than I can remember!
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Old 19 Jun 2009, 12:20 pm
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Join Date: Jun 2009
Location: Walnut, Ca
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Default Re: A/C not cooling and causes RPM's to jump

Thank you both for your advice. The only question I have: Why wouldn't the dealership mechanic be able to identify these problems? Is he just a bonehead or is it really hit or miss?
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Old 19 Jun 2009, 01:02 pm
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Join Date: Jun 2009
Posts: 80
Default Re: A/C not cooling and causes RPM's to jump

A/C issues can be a hit and miss if you've never experienced them before, I'm not very well versed in most problems myself, only the ones I've ran into personally. Remember also that some dealerships pay their mechanics on a per work order + time on work order basis, so a bunch of quick fixes or in and out repairs can equal the same as one big work order like a timing belt changeout, especially if they are tap dancing the times (ie, rounding up to the nearest 15 minutes as I do at the hospital (I get paid hourly, not by workorder )).
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