A/C question

[BarryK]

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??

 

[6880 Mike]

Fan?

 

[BarryK]

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]

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.

 

[Willcox Inc.]

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]

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

 

[BarryK]

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.

 

[vmrod]

maybe bad compressor clutch bearings?

 

[BarryK]

maybe bad compressor clutch bearings?

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

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

 

[vmrod]

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.)

 

[BarryK]

ummm, wouldn't it just be easier to actually use a stethoscope??

 

[Artsvette73]

I would tighten the belt up

 

[BarryK]

yep, that's my first plan of action and will see what happens

 

[MMM]

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]

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.