Noise/vibration with AC on

dshepp806 · dshepp806's Garage

I recently hasd noticed that my '80 cab would exhibit a noticeable vibration while shifting through the gears upward of 5000 RPMS...seemed to be "intermittent"...Now, that it's getting warmer (and running the AC), I've noticed that it is directly related to whether the AC is ON or NOT. With AC OFF, she runs through the gears above 5000 RPMs as smooth as ever. Put the AC on and she has a growl (a vibration, serious deep rattle) when pushed upward of 5000 on shifts.

WTF is this? Something loose? It seemes to be felt most in the tranny/center console area..

Thanks, guys.

Best

Jim727 · 04-21-2007, 08:26 PM

Sounds like the compressor.

dshepp806 · dshepp806's Garage

My bad: that would be 1989,..sorry.

Jim272: how so? What would I check for? AC blows nice and cold!

Thanks,

ipacketeer · ipacketeer's Garage

I would check to make sure that the Compressor mounting bolts are nice and tight

dshepp806 · dshepp806's Garage

will do: TODAY! On a side note: when I changed out the AC belt several Kmiles ago (using same ContiTech belt as before) I marked the mounting bolt postions with felt tip marker. What I have now is not necc. on the original marks. Compressor mounting bolts are now further away (to the right) than before, requiring LESS thread use of the bolt used to make the final tension adjust (on FAR right-horizontal bolt) . Does this have relevance? Tension still ok, irregardless. AGAIN, AC off and she runs through redline shifts perfectly (smooth as a peeled onion!) AC on, and you'd think something was coming loose above 5K RPMS..1-3 gears....

Thanks,

cmonref · 04-22-2007, 05:27 AM

Maybe the belt tension is a little loose. At 5000 RPM, the untensioned segment of the belt may be just loose enough to set up a "thrumming" which would be felt as a vibration. Some might interpret that as a "rattle".

Have you simulated this in the garage with the AC on and off?

ipacketeer · ipacketeer's Garage

Hmmm, I wonder if the Compressor clutch needs to be adjusted to be able to handle the 5K engine RMPs. If the space between the Clutch and the Pulley is not according to the specs it may make shuddering noise.
Hope someone who had experienced similar problem would chime in and put a brighter light on this matter.

Jim727 · 04-22-2007, 08:53 AM

Agree with all of the above. You didn't mention whether you upgraded to a rotary compressor. The older piston-type compressors will always have more vibration than the rotary-type, but you should have some of that vibration below 5000 rpm as well.

Since you did a belt replacement, I would ensure the pulleys are parallel - you don't want the compressor at an angle to the belt. Also, as mentioned, make sure you have all the bolts and they are all tight. Ensure the belt tension is correct; it would not be unusual for a new belt to stretch a bit soon after being installed.

At the unlikely end of the probability spectrum it is possible that an intermittent connection to the compressor clutch would cause it to engage/disengage repeatedly. I'd make sure the electrical connection is intact. Beyond that, if all checks out ok, the issue might be internal to the compressor.

dshepp806 · dshepp806's Garage

Didn't upgrade on the compressor. Pulley line up is goog 2 go.

The vibration is slight below 5000 RPMs , not evident at all in lower rev ranges.

No simulations in the garage. As stated, when she's running on the road, it's a matter of having the AC on then banging through the gears vs. AC off and banging through the gears....night and day, they are.

Not familiar with clutch adjustments on compressor...will check the Bentley for this process.........

I'll report back a bit later........it's amazing how this is transmitted through to the center console.tranny/shifter.

Thanks guys for your observations.

Best,,

Hope to check tension and bolts this evening..

Jim727 · 04-22-2007, 01:31 PM

Doyle -

No clutch adjustments on the compressor. It's magnetic and either engaged or not.

If bolts, belt tension, and other hardware are ok, then consider taking it to your wrench. The York compressor would normally have a slight vibration, but only hands-on will tell if you are in "normal" territory. Could also be just a bit low on refrigerant/oil; if so a vacuum test and charge might save you bigger problems.

dshepp806 · dshepp806's Garage

Thanks Jim727...I checked the system tonight. SHortened up the mounting postion of compressor (closer to pulley),..using a bit more adjustment bolt length....maintaining the same belt tension I had before. Alignment looks good,...BUT:

Did find one mounting bolt (looking at the compressor), far left that would not tighten all the way down,..she's spinning with minimal resistance. Swapped bolt positions with no change. Looks like I've some bad threads within the mounting bracket? Retap, I guess? It's a straight-through shot.. Wonder if this is the problem> ? It's somewhat tight but will NOT give you anything cloase to the torque resting spot.

Compressor, BTW, is a Nippon.

Thanks for your input.

Best,

dshepp806 · dshepp806's Garage

These "normal" vibrations that many speak off (compressor-related),..what is it attributed to?

Thanks, again,

dshepp806 · dshepp806's Garage

Sorry, I forgot to mention that I could not see the sight glass for freon level. Guess I'll have to loosen the retaining straps and turn slightly in order to see it. Probably needs a little bit....I'll let you know.