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A/C question

Joined
Apr 2, 2004
Messages
4,611
Location
Newark, Delaware
Corvette
1965 Coupe L76 / 1978 L82
hi guys

Got back from Carlisle last night. Great show for all of those that couldn't make it but a bit wet on Senday.....

Anyway, brought the '78 back home as it didn't sell which is making the wife very happy. About a 100 miles trip home which is the longest drive the car has seen in YEARS. She ran good I'm glad to say except one thing.
With the A/C on it makes a very noticeable "rattling" noise. Switch off the A/C and it goes away, switch it back on it immediatly comes back. Very annoying!
I had the A/C system completely gone over after I got the car running again in the spring and he replaced the drier/accumulator, replaced all the O Rings, vacuum pressure tested it, and refilled it with freon. It blows nice and cold and works great, almost too cold, but this rattling noise is driving me crazy.
Any ideas??
A friend suggested it might be the bearings on the A/C compressor??
 
Joined
Apr 2, 2004
Messages
4,611
Location
Newark, Delaware
Corvette
1965 Coupe L76 / 1978 L82
nah, don't think so. only happens when the A/C is turned on, not just the blower fan, and the noise coming from the engine compartment not under the dash where the blower fan is.
 

Artsvette73

Well-known member
Joined
Jan 24, 2004
Messages
174
Location
New Jersey
Corvette
1973 Silver coupe, 1977 L48
Check the belt running the compressor maybe loose. Remember the compressor is a pump, if the belt is loose the pump will tend to rattle.
 
Joined
Apr 15, 2005
Messages
40
Location
Wholesale parts 800-588-3883
Barry,

Three things come to mind.

1) It may be the exhaust heat riser valve rattling. The 1978 and 1979 cars are known for this rattle. It sounds like something is loose in the engine compartment when in fact it’s just the valve flapper door rattling in the exhaust. I'd check this first.

2) The compressor may be defective.

3) The alternator belt on your car should have a guide bolted to the upper adjustment arm. Additional duress from the air conditioning compressor may be causing the belt to hit this guild. It’s just a flat little section of metal that bolts direct to the arm.
 

bradfordsvettes

Well-known member
Joined
Mar 28, 2001
Messages
549
Location
Boston, MA area
Corvette
jewel blue 61.cranberry 69 t-top.black rose 92
sounds like the compressor is starting to fail. or possible over charge was it converted to 134? if so it should only be charged to approx 75% of the charge that is recommened for r-12 . also an oil change over is in order r-134 uses a different oil good luck Steve
 
Joined
Apr 2, 2004
Messages
4,611
Location
Newark, Delaware
Corvette
1965 Coupe L76 / 1978 L82
ok, had a couple spare minutes yesterday and did some checking. The rattling noise seems to only be at idle but when giving it some gas so the engine rpm's increase it goes away.
AC compressor belt has approx 1/2" travel movement up or down from it's normal positon - is that the correct amount or is it too loose? Someone mentioned to me that belt deflection should be 1/4"....
it's definitely the AC compressor making the noise as it only happens if I switch the AC on. As soon as the AC is turned off and the compressor switches off the noise immediately stops.
the system was just redone about 2 months ago and it was NOT converted to R134a, it was refilled with the original R12 from a 30lb can of R12 I have.
 
Joined
Apr 2, 2004
Messages
4,611
Location
Newark, Delaware
Corvette
1965 Coupe L76 / 1978 L82
maybe bad compressor clutch bearings?

i wouldn't know, I don't know a thing about AC compressors (or much else for that matter ;LOL )

how would you check for bad bearings or is the noise alone the symptom to indicate that?
 
V

vmrod

Guest
You could take a piece of wood (I use a 1-1/2" thick dowel and about 20" long) and place one side on the compressor near the pulley and put your ear on the other side. Use the wood like a stethoscope and listen for the noise while the engine is running. Be careful where you place the the dowel while the motor is running. You should be able to figure out where the rattling is coming from. (or you should be able to tell where it is not coming from.)
 

MMM

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Joined
Aug 25, 2003
Messages
121
Location
Clayton, NC
Corvette
'63 Coupe, '72 Convert, '02 Z06
Highly doubt if it is the clutch bearings as they are in operation all of the time, whether the compressor is engaged or not. Either the belt (which can be checked with a bar of soap) or internal compressor problems.
Mike
 

snydley55

Member
Joined
May 22, 2006
Messages
17
Location
New Ross, Indiana
Corvette
1978 Silver L82
I just got rid of a similar rattle when my air comp was running at idle when I found the alternator adjusting bolt had sheared. Replacing it removed what I thought was the air cond compressor. Since the alt and air run different belts I am not sure why short of some passed vibration.
 

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