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Unread 09-17-2010, 11:30 PM   #1
lazychris2000
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Location: Anchorage, AK
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A/C compressor knock

Forgive me if this has been posted already--I searched, but I couldn't find anyone else with this problem. Double-forgive me if I ask n00bish questions--I am a little out of my element with this kind of thing.

Youtube video
Above is a video that shows the problem I am having with my 2007 Liberty (3.7L V6). A few weeks ago, my air conditioner just quit working. Literally, it was working great 1 day, then the next day it was blowing warm air-No warning or any indication of problems.
When I turn on the A/C, the compressor makes this horrible knocking noise and the clutch does not engage. According to the cheapo refrigerant guage I picked up, I have enough freon, the fuses are all good, the relay is good and--if this makes a difference--the heat works really well.
I haven't had a chance to jump the low pressure switch because I don't have a garage and it has been raining the last few weekends, so I can't confirm or deny the accuracy of that guage. This weekend is supposed to be nice, so I should be able to test it out tomorrow or sunday. I am a little hesitant to go spend a buncha money on a leak detector kit if I don't have to and, although I am far from an expert, I am leaning towards the problem being with the compressor because of the noise it makes when the A/C is supposed to be running. Is there anything else I should be looking for while I am in there tomorrow? I read through the service manual on the HVAC system and it suggested checking the fuses/relays, jumping the low pressure switch and testing the pressure with a manifold. I don't have $100 to blow on a manifold, so should I try to rent/borrow one. Is that even really necessary?

Any help would be greatly appreciated!


Last edited by lazychris2000; 09-18-2010 at 08:22 PM..
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Unread 09-18-2010, 04:20 PM   #2
richd
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If your clutch is not kicking in,then the compressor isnt turning.So the noise cant be the compressor.I think you better jump you low pressure switch and see if its a bad clutch or switch.Check your wiring for the clutch and make sure there is no broken wire.You also can check the A/C relay in the power distribution center.
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Unread 09-18-2010, 08:21 PM   #3
lazychris2000
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Quote:
Originally Posted by richd View Post
If your clutch is not kicking in,then the compressor isnt turning.So the noise cant be the compressor.
In that case, the noise sounds like it is coming from the compressor. Since the compressor apparently isn't turning, it must be something else near it that is knocking. Guess my next project is investigate the source/cause of that knocking....
I just tried jumping the low pressure switch and the clutch still did not engage. As far as I can tell, there are no broken wires I can see.
I did test the relay and it is working. Even swapped in a known-working one and nothing changed.

Last edited by lazychris2000; 09-18-2010 at 09:24 PM..
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Unread 09-18-2010, 08:36 PM   #4
richd
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Quote:
Originally Posted by lazychris2000 View Post
In that case, the noise sounds like it is coming from the compressor. Since the compressor apparently isn't turning, it must be something else near it that is knocking.
I just tried jumping the low pressure switch and the clutch still did not engage. As far as I can tell, there are no broken wires I can see.
I did test the relay and it is working. Even swapped in a known-working one and nothing changed.
If you jumped the wires and the clutch didnt kick in,then I would say the clutch is bad.Double check the wires at the clutch coil,I have seen and heard of broken wires near the coil.Here is the section in the service manual and will tell you how to check the coil,and the relays,it starts on page 12:

http://www.scribd.com/doc/3287208/Je...F-Secc-24-HVAC
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Unread 09-18-2010, 09:23 PM   #5
lazychris2000
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I guess its better than the compressor being bad....still gonna be a PITA to fix, tho. I will definitely triple check the cables. Other than checking for obvious problems with the cable (broken insulation, exposed wires, etc), is there anything else I should be looking for that would be an indication of a bad cable?
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Unread 09-18-2010, 10:16 PM   #6
richd
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Quote:
Originally Posted by lazychris2000 View Post
I guess its better than the compressor being bad....still gonna be a PITA to fix, tho. I will definitely triple check the cables. Other than checking for obvious problems with the cable (broken insulation, exposed wires, etc), is there anything else I should be looking for that would be an indication of a bad cable?
If you put 12v to the clutch and it doesnt kick in,its either bad wiring or bad clutch.Does the cooling fan go on when you press the A/C button?If the fan doesnt work,the A/C wont work.
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Unread 09-18-2010, 10:29 PM   #7
lazychris2000
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I am a little hesitant to plug it straight into the battery...I wouldn't want to blow anything up, so unless jumping the low pressure switch does the same thing, I would feel alot more comfortable leaving that to an expert.
Yes, the fan does turn on.
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Unread 09-19-2010, 02:54 PM   #8
richd
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Originally Posted by lazychris2000 View Post
I am a little hesitant to plug it straight into the battery...I wouldn't want to blow anything up, so unless jumping the low pressure switch does the same thing, I would feel alot more comfortable leaving that to an expert.
Yes, the fan does turn on.
If you have a voltmeter,see if there is 12volts going to the clutch coil.You have to have it running with A/C on fan on low speed.Check the volts on your battery,then check for voltage at the coil,it has to be within .2 volts of the battery volts.If you have the volts to coil ,then bad coil,if you have no volts going to coil,check the wiring.
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Unread 09-27-2010, 01:23 PM   #9
lazychris2000
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This week has been absolutely crazy, but I finally got a chance to check out the voltage. It is almost spot on with the battery voltage. Guess I need a new clutch, eh? Is there anything else that could be an issue?
Thanks for all your help, btw!
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Unread 09-27-2010, 01:40 PM   #10
richd
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Originally Posted by lazychris2000 View Post
This week has been absolutely crazy, but I finally got a chance to check out the voltage. It is almost spot on with the battery voltage. Guess I need a new clutch, eh? Is there anything else that could be an issue?
Thanks for all your help, btw!
If you have the volts going to the clutch,and clutch doesnt work,then I would say the coil is bad and need new clutch.
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Unread 09-27-2010, 01:41 PM   #11
lazychris2000
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On the plus side, it doesn't seem to need a new compressor, so come summer it should be a bit cheaper to fix.
Thanks again for all your help!
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Unread 09-27-2010, 01:54 PM   #12
richd
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Originally Posted by lazychris2000 View Post
On the plus side, it doesn't seem to need a new compressor, so come summer it should be a bit cheaper to fix.
Thanks again for all your help!
No problem,There is something you can try,with everything off,take a small hammer and tap on the front of the clutch,and then see if it works,if not the replace clutch,and Good Luck.
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