A/C Compressor Mounting Bolt
 

I have a strange situation I'd like some ideas on. Car is an '87 924S NA.

Short Version: Twice over the course of the past three weeks the upper-front mounting bolt on the Air Conditioning compressor has sheared the head off.

Any idea as to why?

Long Version:A few weeks ago I did a complete belts, hoses and FOES replacement. Since that time the car has run great! Smooth and strong. A couple of weeks ago the A/C belt started squealing and I attributed it to "stretch" from a new belt. What I discovered instead was that the upper-front compressor mounting belt had sheared it's head.

I thought that it "might" have happened that when I was putting things back together that the bolt "might" have seemed soft and I "might" have over-torqued it and maybe this was "my fault." So I got a drilled out the broken stud, popped in a replacement M10-1.50 and buttoned everything back together. Good to go.

Maybe a week later, the squeal is back. This time, besides the top bolt being sheared, the end of one of the banjo bolts on the tensioner was sheared too. Really odd, I thought, but "maybe" (I thought) the banjo bolt had stressed / cracked with the breaking of the bolt before, so "maybe" it was ready to break and I didn't notice. And then, when it let go, "maybe" the stress of the compressor hanging on its own cause the bolt to give way. (See how good I'm getting at making up stuff?)

I popped in a new (complete) tensioner, drilled out the broken stud again, double-checked everything under the hood, put everything back together nice and tidy. Good to go, back on the road.

Yesterday, after he used the car to go to soccer practice, my boy tells me the squeal is back and -- sure enough -- the upper bolt has sheared off its head again.

What. The. Hell!?!?!

The belt looks perfect; not a sign anywhere of any fraying or stretching, so I doubt it's a pulley-mis-alignment problem, but I ain't too proud to admit: I'm out of ideas.

Any ideas, people? (I'll be out in the garage drilling out a broken stud if you need me.)

...sjs...

You have to leave the pivot bolt and tensioner bolt loose while tensioning. If you try to adjust the tensioner with those bolts already locked down, they will shear off or break the ear off the compressor.

So, loosen all mounting bolts... adjust tensioner to desired tension... retorque mounting bolts.

Amen to that :cool:

I'm almost certain that, the last go-round, I put everything together "finger tight", then tensioned the belt, then tightened the turnbuckle nuts in the tensioner, then the bolt-ends on the tensioner, then (finally) tightening the upper mounting bolts on the compressor, front then rear.

I know for a *FACT* that this is the reassembly sequence I just used to replace the sheared bolt this morning.

One thing I noticed, and I don't know if this matters or not. I noticed in PET that the inboard end of the tensioner has a "collar" inside the banjo bolt. PET shows this collar facing to the rear of the car. I had it facing the front. A careful study revealed that this actually "cocks" the tensioner about 10-15 degrees one way or the other, so this time I put to collar the the rear. Maybe, just maybe, it's possible that this twisty torque on the bottom of the compressor, and maybe a less-than-scrupulous mounting technique on previous attempts, have all conspired against me for a batch of bad car-ma.

It's back on the road. Mounted exactly to the correct procedure.

Cross your fingers with me, and thanks for the quick and helpful replies.

...sjs...

Is the compressor already cracked?

If the compressor is cracked, I can't see it. I had the opportunity to examine it *very* closely as I was drilling out the broken bolt. Both the front and rear mount (holes) are intact and have good threads.

I also looked very carefully at the mounting bracket (attached to the engine block). It looks good, too.

I took the car for a shakedown cruise yesterday and, so far so good; nothing sheared. That's a refreshing change!

...sjs...

A/C Compressor - Post-mortem
 

Well, after posting the previous note, the accursed thing sheared off the A/C Compressor mounting bracket again. Not once, but twice! The final time it -- again -- broke the banjo bolt on the tensioner. (That totals 5 sheared bolts, and two sheared tensioners, for those of you keeping score at home.)

I was at my wit's end when my teenage boy mentioned that he was noticing a correlation between turning on the A/C and the dreaded squeal.

I suspected that, maybe, the compressor was spontaneously freezing and the stress was then taking the mounting bolts with it.

So I repaired the broken hardware again, and then unplugged the A/C clutch wire to disable it. Since then, no problems.

1st question: Any tips or pointers on how to determine if, in fact, the compressor is stalling and the torque on the belt is causing the bolts to yield ungracefully? (This is just my working theory, and it's based purely on my speculation. I haven't discovered any supporting evidence in going through the archives, so it could be complete fiction!)

Background:
This car is an ongoing project. The A/C didn't blow cold when I bought it, but the PO indicated that it "just needed a charge" and that he'd had the system converted to R-134a a few years ago.

I got a re-charge kit from Wally-World; the kind that has the gauge and includes (in one can) oil and some purported sealing capabilities. I charged the system to 80% and got temps in the cabin between 45 and 50 degrees. That was a month ago. Now that I think about it, that was about the same time as this bolt mystery started to become such a puzzle.

2nd question: Any suggestions on maybe repairing the A/C system? I've heard that it's possible to rebuild these compressors, so maybe a full flush, rebuild and recharge is in order. But I'm having difficulty finding a local service who is willing / able to rebuild the compressor. And a replacement compressor (even a rebuilt) just isn't in my boy's budget right now.

Sounds to me as if the compressor is laboring because there is too much oil in the system and/or the system may have been charged with the can upside down, which is a liquid charge, damaging the compressor.

Spin the hub on the front of the clutch. How does it feel? Pull the belt, how does the pulley feel?

Don't use cans of refrigerant with oil and never, ever use ones with leak seal.

Definitely time to have the system evacuated, measured with proper manifold gauges, and recharged correctly. You just can't tell what the charge is on both high and low sides with a single can-mounted gauge.

If it's going into over-pressure it'll blow the compressor and/or some expensive bits buried *way* up under the dash.

Is a salvaged compressor in the budget?

sit there, revv the engine up, and hold it around the same RPM as when driving (with the AC on, or whatever was being used when it messed up) and watch to see what happens. Observation can tell you a lot of things...

Oh, and invest in a set of real gauges. A person I know got one of those crap cans from wal-mart, and the gauge on that can showed 70PSI on the low side to be in the "green" (or fully charged) range and that's WAY overcharged. I don't like to have any more than 35PSI on the low.. It blew the front seal out in the compressor, and smoked and ruined the clutch.

Do not buy the Harbor Freight gauges, they leak like a sieve. The pressure on both sides is quite dependent on the ambient temperature, so we might not be able to say that a given pressure is "too high" or "too low" without first saying what temperature it's at.

You guys have convinced me: It's time to "bring it somewhere." I'm out of my depth with HVAC stuff. I get the theory, but in practice it's way more sophisticated than I can grasp.

I have been looking for rebuilt compressors, and it seems that $500+ is the range. I tried dcAuto to see if they had a "recycled" one, but they're out-of-stock.

I contacted a local shop and asked if they could rebuild / reseal the one that's in there, and they said they wouldn't, and didn't know of anyone local who would/could.

So... The good news is: Fall is in the air; I've got maybe 6 months to budget, save for the $1,000 before the Central Virginia weather turns (ahem) "balmy" again.

I appreciate all the insight and support afforded by this forum. Really does make owning a classic Porsche affordable(er).

...sjs...

You could check ebay for a rebuilt.
This is just an example if you search---others available. Old, junk, nearly used, or lightly used by my grandmother are just BAD

AC Compressor Kit Porsche 924 928 944 968 | eBay

You have to get a compressor built for a '87 924S or 944 with correct mounting ears. Nippondenso 10P15E is the basic unit.

If you have a higher budget check out Porsche Air Conditioning,Porsche compressor,Porsche condenser,Porshe condensers,Porsche drier,Porsche driers,Porsche evaporator,Porsche evaporators,Porshe barrier hoses,Porsche air conditioning upgrades,Porsche air conditioning updates,Porsche air co

Note: the PAG100 in the picture is too heavy. Porsche oil is ND8 and that is PAG50.
Better still use POE-100 blends with old oil in system very well. Or use PAG 50 oil.

GL
J_AZ

Wow, John, THANKS! That Griffiths link was just what I needed.

That Kuehl kit @ $599 seems like just the ticket.

You rock!

...sjs...