So let's talk about dealer A/C for a moment

[Dorsai]

As they say...when it rains, it pours.  I've had this truck for nearly nine years and in that time it has given me very little trouble.  But now that I'm planning on taking it for a road trip, it's suddenly one thing after another.

Now it's the air conditioning.  I've started getting an intermittent screech/shriek when the A/C is running.  It doesn't happen constantly, and when it's not happening I can sometimes force the noise by running the engine at high RPM.  My belts (dual belt pulley on a York compressor) are in good condition and seem to be reasonably tight.  The A/C itself seems to work fine, and blows nice and cold.  I don't notice the engine trying to bog when the noise happens, either.  And if I turn the A/C off the noise goes away and doesn't happen no matter how high I rev the engine.

Anyway, my guess is that it's either a bearing in the compressor, or something in the compressor clutch.  Is there a good way to determine which it is (if either) before I start taking things apart?  

[Gary Lewis]

Check the belts for glazing.  And potentially buy a stick of the belt dressing that is intended to make them not slip.  That's cheap and won't hurt anything.

But, the shrieks I've heard on A/C compressors have been the clutch.  So I'd set the fast idle on the carb and run the A/C with the hood open and observe the belt/clutch/compressor crankshaft when the sound happens.  If the clutch is slipping you may be able to tell, and when the engine is then shut off the clutch will probably be hot.

As for a bearing in the compressor, I've not heard one do that.  Those York compressors are tough and with the oil circulating in the system there shouldn't be an issue.

Also, has the system been recharged lately?  If so you may have too much pressure, making it hard for the clutch to get the compressor going.

[Steve83]

Look at the belts while the engine is running; particularly while they're screeching.  It might be obvious enough to see the belt vibrating.  You might also see an abnormally-shiny ring on a pulley, or some other wear.  Pay special attention to each belt remaining in one plane (geometrically) over its entire span - a pulley too far forward or back can cause noise.  Try to carefully pinpoint the noise with a mechanic's stethoscope, but don't let it or your sleeves or skin get tangled in the belts.

[Dorsai]

Good advice there gentlemen, thanks.

Belt tension is good (at least it was when I last checked a couple weeks ago), and they're all in plane...I haven't checked specifically for glazing however.  Belt dressing couldn't hurt.  A/C hasn't been recharged in at least a couple of years, so I don't think that could be the problem.

Tomorrow's to-do list is now (1) get the new starter installed, (2) start the PB Blaster presoak of the U-joint hardware, and now (3) start isolating my A/C noise.  Good thing I already had tomorrow off work.

Aren't to-do lists supposed to get shorter as you go?

[Gary Lewis]

My to-do lists are continually expanding.  But then, I get a kick out of ticking things off the list.  

[ArdWrknTrk]

Dorsai wrote

Aren't to-do lists supposed to get shorter as you go?

LOL.....
It never seems to work that way.

Did your parents move you out of Florida on a turnip truck, by chance?   

[Dorsai]

ArdWrknTrk wrote

Did your parents move you out of Florida on a turnip truck, by chance?  

No, but I suppose there could have been some turnips in the hold of the 727.   I don't recall falling off the plane, though...

[ArdWrknTrk]

Well, don't get frustrated by the growing list.

You're doing a great job, and noticing these things just shows you're more in touch with your grandpa's truck.

[PetesPonies]

Most times, it is the belt, even if you think it is fine. Belts make that noise, not much else does. And it's like looking for a vibration . .you think the u-joints are tight. You grab and push and pull, no movement.But when you disassemble the joint, it's worn like anything. Same with upper control arms on vintage Mustangs. They are noisy when worn. You won't get any play out of it . . but take it apart and you'll be surprised you have died yet :)

[Steve83]

Dorsai wrote

Belt dressing couldn't hurt.

Ford & most belt mfrs. say NEVER to use belt dressing.  Only mild soap (detergent, surfactant) and lots of water.



Most of this caption applies to V-belts:

[1986F150Six]

Dorsai, are the twin compressor belts a matched pair? Were they installed at the same time?

[Dorsai]

1986F150Six wrote

Dorsai, are the twin compressor belts a matched pair? Were they installed at the same time?

They’re each the same part number, and were put on together in 2012 or so...I’d certainly call them matched unless there’s something else to the definition.

[1986F150Six]

Belts can be purchased in factory matched pairs, for applications as this. I guess the tolerances are more closely matched. If one purchases the same part number in separate packages, one may be slightly longer.

[Dorsai]

They’re not matched to that extent, no.

[1986F150Six]

Maybe one has stretched to the point of chirping?

[Dorsai]

1986F150Six wrote

Maybe one has stretched to the point of chirping?

Maybe?  Although by this point (~7 years on) surely the shorter of the two would have stretched to the length of the longer, and they'd be the same length by this point.

[Gary Lewis]

Matched pairs are important for applications like this.  I'd swap belts long before I tear into a clutch or compressor.

[Dorsai]

Gary Lewis wrote

Matched pairs are important for applications like this.  I'd swap belts long before I tear into a clutch or compressor.

Agreed.  I'm going to take a close look at the belts after a bit when I change out the starter.  

But I'll admit, I'm not sold on the notion that lack of matching has anything to do with this.  Maybe if they were new belts, sure.  But seven years on?  I bet they're identical now to the millimeter.

When I go back to NAPA to return my starter core, I'll ask that nice counter girl if she's got a matched pair.  What's the worst that can happen?

[1986F150Six]

Dorsai wrote

Gary Lewis wrote

Matched pairs are important for applications like this.  I'd swap belts long before I tear into a clutch or compressor.

When I go back to NAPA to return my starter core, I'll ask that nice counter girl if she's got a matched pair.  What's the worst that can happen?

You could get slapped?

[Gary Lewis]

Please video that.  I gotta see it.