Have a 1998 Chevrolet Camaro SS convertible. My air conditioning compressor started making a knocking noise like my motor was running out of oil or something but it's coming for the air conditioning compressor. That's just the kind of sound it is it gets faster when I rev the engine I can't see where the clutch or the pulley or hitting anything and I've changed the compressor and the dryer and it still does the same thing. Sometimes it's louder than others. Does anybody have any ideas?

 

Well if you replaced the AC pump and the noise is still there it's obviously not the pump.
Are you sure it's the AC making the noise?
Maybe a bad idler pulley?
Maybe you should take the belt off and start the engine to make sure it's not something internal,belt off and no noise you can start eliminating things and assume it's not in the motor.
Noises can travel and fool you,alternator,water pump?
If the noise goes away with the belt off before replacing it spin these items by hand to see how they feel and sound.
Did you replace the compressor pump with new or used? Not likely it would be a bad new pump but anything is possible.

 

One detail I left out. It seems that when I turn the air conditioning blower motor higher the sound gets louder and when I turn the blower all the way down sometimes it almost goes away and it times it actually has gone away. Because it only happens when I turn the air conditioning compressor on I'm not sure how taking the belt off would really affect anything because then the air conditioner compressor wouldn't actually be working. I will get under there and take off the idler pulley and the tension pulley and make sure they're running smoothly. But I've never heard a pulley sound like this like I said it literally sounds like my car engine is out of oil or I've thrown a rod that's how bad it is. You would think I'd be able to track it down a little bit closer. I thought maybe it was my motor blower but that thought came only out of desperation. If it was the blower motor I would think I would hear it inside of the car and not underneath the hood. I've been wrong with simpler things before though. I'm thinking obviously it's not the compressor because my old one made the same sound and when I took it out it was a little sloppy and needed replacing anyhow but to have two compressors that make the same noise like this that nobody seemed to have heard of is beyond my comprehension. I'm on SSI but I think I might have to go back to work to be able to afford to put it in the shop and buy shop I mean the actual Chevy dealer. I cringed to think I have to do that because they charge so much and I've always prided myself on being able to solve almost any problem but this one really has me stumped.

 

It may be your heater/AC fan.
Leave the motor off and turn the key on then hit the fan switch.

 

What he said but also look for a cracked bracket on the compressor. If the change in noise instant when you hit the fan or does it get lag behind, I an talking about turn the fan down and noise quiets 30-45 seconds later? Was the compressor replaced by a pro? Was the system vacuumed down? I assume there was no sign the dryer failed it was just replaced due to the process?

 

His car has no air conditioning bracket to bolt to, itbolts directly to the block. When you talk about a lag time yes there is. When I turn the blower all the way high and it's at the loudest knocking noise as I turn it down the noise slowly decreases not all at once but gradually. If I turn it from high all the way to low the noise will gradually decrease and it could completely stop anywhere from 5 to 15 seconds maybe. Also if I rev the motor to hire RPM and not a lot the noise goes away. I'm not saying it's always been that way but that's the way it seems lately. Keep in mind I only have one can of freon in it because that's enough to get the compressor on and I didn't want to waste another can for nothing. In other words if I have to replace something in the system is open there goes another can $15 down the tubes. I'm trying not to make the descriptions I'm giving long and drawn out where people lose interest and not want to read them but for good measure I'm going to start at the beginning explaining what I did and why as best I can. To begin with my air conditioning compressor started making a loud knocking noise similar to as if I'd thrown a rod in my engine. It was that loud at times it started out not very loud but over time continue to get worse I thought for sure is my compressor so I took the compressor out and changed it no I didn't vacuum the system nor did I vacuum it before I replaced the freon 134a. Even though it didn't seem to be blowing as cold as I had hoped it still was doing the job I ran it for possibly 10 or 15 minutes and there wasn't any noise at all but by the next day all the freon had leaked out. I never had a leak before but apparently I had damaged the hose that goes to the condenser. Put a hole in it so I had to replace that hose but it's a two-part hose that goes from the compressor to the dryer and the other one goes to the condenser. Course I had to take the compressor out to do it and all this time I didn't detect any problem with the compressor or the idler pulley or the tension pulley although I will admit I really didn't check them closely or spin them to see how they were functioning the belt is good. After I recharge the system the noise was back again. I should have changed the dryer anyhow but at this point I was assuming it was full or just bad I thought maybe there was too much oil in the system and rather than the compressor compressing gas to liquid it was trying to compress liquid which is we all know will not compress and that might have been what was making the knocking noise. I replaced the dryer and put one can of freon into the system the compressor came on and even though it took a little longer the air conditioning did get extremely cold but still the noise is there. When I'm under the hood it could be quite loud so loud in fact I can practically feel it and it sounds or feels like I threw a rod in the engine but that's not the case it gets louder when I turn the blower motor on high and usually the sound can disappear all together when I turn it on low. When it's making noise I give it a little bit of throttle and the noise goes away but still I only have one can of freon in it and it needs another I was just afraid if I had another it might be even worse. So that's where I stand that's the best explanation I can give. Fromunderneath I can't see anywhere that it's hitting or rubbing. One last piece of the puzzle that in my mind it's not very significant given the fact that the other compressor was doing the same thing and all of the symptoms combined. The second time I was taking the compressor out it slipped for my hands and fell about 6 in onto the asphalt landing on the clutch. Question appear to be damaged and I can't tribute that to this problem because the other compressor did the exact same thing. At the same time when I replaced the compressor the first time before it ran out of freon because of the leak in the hose it wasn't making the knocking noise then that I could detect although I really didn't run it very long. I know I'm going to get a lot of suggestions saying that I damaged the clutch and that's my problem but to me that doesn't explain why the first one did it and how come the noise seems to go away when I turn the blower motor all the way down. Sorry for the rambling description but I thought this time I should give as much detail as possible if I can expect any help from anyone. If you manage to hang with it this long thank you for reading it and thank you all except any help I can get with gratitude.

 

Did you follow the manual guide lines for adding oil? if there is too much oil in the low side hose or the compressor it could cause compressor. failure. Hydro lock is instant.

I cannot tell you what is wrong with your system in a post, I am not one of those this happened to me so it must be what is happening to you kind of guys. Here are some of my thoughts on your thread.

I agree based on what you said that this is a high pressure issue. Since you have a variable displacement type compressor it takes a little time to build pressure, the lag you mentioned. What are those high pressures? if you building crazy pressure that could damage the compressor. I do kind of doubt that is the case because you are low on refrigerant. I do have other concerns that may cause high pressures. Your system could have normal high side pressure with a damaged compressor.

What could cause really high side pressure. Blockage of a line along with a failing high pressure switch, most of the time blockage happens at the entry of the evaporator. Again most of the time blockage is cause by the silicon bag in the dryer receiver breaking and letting its content into the system. Another thing that can plug up a system is moisture. Even a tiny amount of moisture can form ice beads that can plug up the system and/or damage the compressor. The fact you did not vacuum the system down could cause these symptoms. I have even seen people that have had issues because they only vacuumed the system for a half and hour. They did not understand they where not sucking the moisture that they where dropping the pressure so the water can boil out. Just like on your oven just because the water starts to boil does not mean its all gone. 2 hours at 25 inchs is probably ok, I do 4 hours if I am not be rushed.

You may think what are the chances you would get a high pressure switch failure and blockage in the same car. In a system that is the high pressure switch is never triggered 23 year later she can be lockup tight. If you are having crazy pressures the noise may go away once they return to normal.

Running your system low on refrigerant is not a good idea. Your refrigerant is what circulates the oil. If you have low flow do to blockage or low refrigerant that can damage the compressor.

If at least one of your fans in the front must be working with the AC on. If not it can cause high pressures.

Don't discount flukes, getting a new part that has the same failure as the old one is possible. Statistically speaking it will happen to someone. I have seen good mechanics go crazy because they assumed a new part could not be defective.

You won't like this part.
If I was working in a shop and I saw a customer report like your post. I would verify the high and low side pressure if they where close to normal I would use a stethoscope to verify the source of the noise and if the noise was coming from the compressor I would pull the orifice tube and verify there was nothing blocking it. If there was I would have to flush the entire system. I would then replace the orifice tube, dryer receiver and the compressor, in this case I would draw the system down for the 4-6 hours fill her up check for leaks and send it down the road. It is really the only way to fix this and be sure I would not get a come back. I would just assume it was an oil or water issue. I AM NOT SAYING THAT IS WHAT YOU SHOULD DO. But I know what a failed variable displacement compressor sounds like. Once you eliminate all other issues its all that is left.