Hello All,

I am having a very annoying matter with my 2000 MC SS 3.8. I can hear a knocking sound in the engine. The knocking only happens when the AC is on. The AC is blowing very very cold air. I did have an issue before with my car shaking while the A/C was on. First thought was the A/C Compressor was going bad but the air was very cold. After some investigation I noticed the pulley tensioner wheel was not turning freely, so I've replaced the entire belt pulley tensioner a couple weeks ago. In which the shaking has stopped completely but the knocking remains. With the A/C off there is no knocking. I'm kind of thinking it is the A/C compressor I'm also thinking maybe it is my lower intake manifold because the sound seems to be coming from that general area. The A/C compressor I think is fine as there is no shaking and the air is super cold.

A little back story on my manifold replacement:
Some 7 months back on my way to work, my MC started shaking a lot as I accelerated then eventually overheated and started smoking really bad. I had it towed to Calverts. The mechanic informed me that the lower intake manifold needed to be replaced. The cost was for $900+. I didn't have the cash so I went to pick n pull and removed the upper and lower intake manifolds off a 2001 Monte Carlo SS. I did however buy a brand new gaskets for the upper and lower intake manifolds.
The replacement went perfect. My MC was extremely quiet and drove excellent. Like when I first got her in 2000.

Now 7 months later the above issue is happening. Any help, opinions and or suggestions would be much appreciated. If I need to provide more details please let me know.

Thanks

 

Well I started noticing a highpitch whining noise here as of late along with the knocking sound. So I went ahead and replaced the lower intake manifold. The high pitch sound is no more. The car is once again very quiet. Except when I turn on the AC. Now to give even further detail on this knocking sound. I can turn on the AC actually and there is no sound at all but once I press the AC button the knock begins.
The air is extremely cold but the knocking is annoying. I'm guessing the AC compressor is needing to be replace brut I'm not sure how to drain the system.

Any suggestion?

 

First of all, you're not really turning on the AC until you push the AC button. The compressor pulley turns, but the compressor clutch is not engaged until you push the button. Sounds like the AC compressor clutch is going out. The clutch itself can be replaced but the compressor still has to be removed from the vehicle, so unless you have real low miles you'd be better off replacing the whole thing. A good quality compressor runs about $350.00 including a new accumulator and orrifice's. This involves draining (recovering) the refrigerant with a vacuum pump and transferring it to an empty refrigerant bottle. Unless you know an HVAC guy like I did you'll need to take it to a shop to have the system vacuumed to recover the refrigerant. It's illegal and harmful to the ozone to freely discharge CFC's from the refrigerant. You will also want to replace the accumulator, and it's recommended to replace a couple orifices, but they're a pain to get to and not absolutely necessary unless you have a catastrophic failure known as "Black Death". You will also want to replace any O-rings on the fittings you take apart. A complete kit runs about $5.00. Once you have everything put back together the system needs to be put back under vacuum again and refrigerant weighed to proper amount and added to the system to the proper charge measured with a Hi-Low AC manifold pressure gauge. A shop might charge $1,300.00-$1,500.00 for the whole job. It's not that hard to do, but takes the right equipment and know how, or should I say "know who", Lol.


Good luck, hope this helps.

 

DAMN it. Yeah I was just reading up on this possibility a bit ago. I have a buddy that works for an auto shop and he also said it could be the clutch. I'm kinda relieved as he said he can empty the system for me. But I'll have to do the other work. Which I'm fine with.
@plumbob I truly appreciate your response. You even gave me a better insight on this matter. I will first attempt to replace the clutch and see where that goes.

 

I'm going to attempt to replace the AC Clutch and since I'm going to be under the car maybe even the ac pulley. I've read that there are specs I should be aware of between the clutch and pulley. Would you or anyone have any idea what the specs would be for a 2000 MC SS?

 

Josh.
I've never replaced the clutch alone, but fair warning- The factory service manual calls for 4 special tools.

1. J 33013-B Hub and Drive Plate Remover and Installer.
2. J 33022 Shaft Nut Socket.
3. J 33027-A Clutch Hub Holding Tool.
4. J 34992 Compressor Holding Tool.

You can probably improvise on some or all of these. Just letting you know.


Lots of precautions about alignments, pounding, over-screwing.


I discourage trying this yourself, but it's your car man. More power to you and I'll be impressed if your successful.

The gap between the frictional surfaces of the clutch plate and the clutch rotor needs to be .016-.020 in.

The only other "clearance" thing is to verify the shaft key is even or slightly above the clutch hub before installing the shaft nut.


God luck! Keep us posted.

 

Hey guys I'm back with an update on my AC Compressor. Sorry for my late response but after being laid off work I've not had much time to update the website. But after a failed AC Clutch and 2 partially used AC Compressors that didn't fix the knocking sound when my air conditioning was on. I finally decided to go get a brand new AC Compressor. Slapped that baby in Saturday filled it up with refrigerant oil and freon. There is no horrible knocking sound and the air blows very cold like before.

Hooray me.

All the shops wanted to charge me $600+. I spent about $200 would have been less if the other compressor would have worked. Like $400 less.

 

Glad it worked out. Stay coooo......

 

Also thank you very much Plumbob. I was able to get my hands on a Clutch Tool Kit Plate remover/Installer. It was a task finding the correct one as well as the feeler guages. I truly appreciate the help.

My next project is replacing the turn signal / high beam switch. That should be fairly easy

 

The multifunction switch replacement is fairly easy, but does require a couple special tools like and internal torx bit to remove the screw on the bottom of the steering column. Seems like there's one other too, but can't think of exactly what it is right now. You'll figure it out.