A/C compressor vibration
Thread Starter
Racer
Joined: Aug 2002
Posts: 269
Likes: 0
From: Lexington ky
A/C compressor vibration
I have been tackling several issues with my car the fast few weeks one of witch was the a/c. I got everything on and then had a shop (I hope they did) vacuum and refill the system. The system blows fairly cold but when the compressor kicks on it draws my engine down a lot and ads lots of vibration. Is this normal, do I need a new compressor or clutch? Any help would be greatly appreciated; I would hate the trial and error approach on high dollar parts 
J
J
Racer
Joined: Nov 2000
Posts: 290
Likes: 0
From: Omaha, NE
I see you have an 81 4-speed so you won't have a carb solenoid to compensate for the extra load when the compressor engages and this is probably the reason you are feeling engine "drag" at low rpm. For excessive vibration make sure all the brackets are on the engine and tight. Frequently the compressor support rod back to the intake manifold is not re-installed when intakes are changed and that rod will make a huge difference in vibration damping-especially at low rpm. Good luck.
Thread Starter
Racer
Joined: Aug 2002
Posts: 269
Likes: 0
From: Lexington ky
the bracket is on and intact, it just seems the compressor has way to much drag and that makes me think it is going bad. i really dont know what all the compressor actually consists of though
Race Director
Joined: Feb 2005
Posts: 16,100
Likes: 17
I have A/C on my 78....the clutch went out in my old one...metal filings were imbeded in my hood insulation...check your insulation/hood above compressor to see if it throwing oil...(they have a tendacy to load engine down giving that feeling of vibration)...examine the clutch...just forward of the belt(pulley).Check for metal filings,just in case...
Safety Car
Joined: Oct 1999
Posts: 4,101
Likes: 10
From: NorCal
Check this...
One of the most common causes of vibration with a C-4 style compressors is a loose belt. All you have to do is fire up the A/C and watch the belt. If it's dancing ("vibrating"), try tightening it a bit, or replace it with a better quality belt. Also, C-4's are notorious for using a LOT of horsepower to run. There are some nice kits out there to convert to a Sanden,Denso or Sankyo compressor, which are much better compressors. Only compressors I've seen that are worse than GM rotaries is the junk installed on BMW's.
Hans
Hans
Thread Starter
Racer
Joined: Aug 2002
Posts: 269
Likes: 0
From: Lexington ky
I checked for metal flakes and oil but do not see anything and my engine is fairly clean. If they did not vacuum the system out well or under fill would that cause it? Can i just go buy a can and add myself?
Racer
Joined: Nov 2000
Posts: 290
Likes: 0
From: Omaha, NE
On my 79 the system takes 3 lbs. Without gauges and other AC equipment I think you would be asking for more problems by adding R-12 at random-IF you can buy it from someone. The sensation of "drag" is pretty subjective so here is my experience: cruising a very flat Interstate highway at ~2800 rpm with L82/M-21/3.70 rear I can definitely feel when the compressor cycles. This is an irritating, but not critical, amount of drag IMHO and it seems to be normal for these R-4 style compressors. I usually don't drive it on brutally hot days because of this. Good luck.
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Le Mans Master
Joined: Jan 2004
Posts: 8,295
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From: one night in Bangkok you are never lonely
I had many problems with my C-4 so I just changed to a Sanden and it runs smoother on the road but I am still fighting stop and go traffic A/C failure. The temps here run mid to high 90 every day and when I get stuck at long lights or in stopped traffic the A/C goes hot as there is no air crossing the evaporator. It looks like I will have to add a fan to the front of the radiator like some others have done. I really don’t want to do this as the hood has to restricted to not crush the added fan. 
Race Director
Joined: Apr 1999
Posts: 11,520
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From: CORVETTE 77 385 C.I. TEXAS
The belt should be tight as Wrencher said. You may be low on freon.
Maybe there is an adj. on the low pressure switch. When I had the R4 the cycling was only when low on freon (like when replacing the comp.). Have spun the belt off a few times at high rpm even when tight.
Maybe there is an adj. on the low pressure switch. When I had the R4 the cycling was only when low on freon (like when replacing the comp.). Have spun the belt off a few times at high rpm even when tight.
