A Cautionary Tale---81 300D w/84 Powertrain---R4 A/C Compressor Explosion
 

Howdy all,

Just had work done on my '81 300D (that has an '84's engine and tranny) to replace a bad R4 A/C compressor. The new one...exploded. Yes, exploded. My mechanic says it blew the case. Was frightening and I believe had someone been in or near the engine bay at the time of occurrence, serious injury would have likely been the result. Now, the details.

So, my mechanic replaced a bad R4 with a new unit. Along with that, there was a cut in a hose (the A/C Manifold hose---either part # 13-029 or 13-030 in my father's ancient Performance Products catalog, from Fall/Winter 2008). Before he could replace the R4, my mechanic had a difficult time finding the part; I found a local Napa which repaired the rubber hose with new. The repair looked very sturdy and capable of holding the pressure of an A/C system. After receiving it, repair was all systems go.

Upon picking up the car, he told me the car's A/C ran around 50 degrees, but that it probably wouldn't cool the best in town due to what he thought was an incorrectly working front auxiliary fan. Believe he said it was sucking air in instead of blowing it off the condenser. The final price tag for the repair was somewhere between cheap and expensive, a repair that, after hearing the final total (included replacing a rusted ball joint) made me think to myself that I've spent a lot of money on an older car. Oh well, it was time for the test drive.

Driving it around town...was...not so good. With the windows closed on a 90 degree day, the air coming out of the vents in MIN position was cool, but not cold. I also noticed a severe loss of power with the A/C on. I decided to drive it to a town 30 minutes away; figured I needed to check it via highway, if it still didn't work very well, then go to Plan B (talk to mechanic about solution to issue). I thought I noticed a bit of metal-to-metal rattling as I drove, but wasn't sure. The cooling was better, but not enough to use on a regular basis. Also, my coolant temp gauge rose to a needle's width above the 100C mark as I drove on the highway; the highest it has ever been.

Upon arriving, pulled into a a shopping center parking lot, and opened the hood. Immediately, I noticed the engine was severely loping and shaking, almost to the point of near shutting off. I decided to turn off the A/C, and the car returned to normal. Looking around in the engine bay, I saw nothing out of the ordinary, but knew full well things weren't right. Oh well, let's go get a bite to eat, I thought.

So, I pulled into a restaurant's parking lot, and decided to look at the A/C again. Now, I started hearing that intermittent metal "screeching" sound I thought I heard on the highway. I opened the hood to look around; saw nothing out of the ordinary. Decided to get back into the car and shut off the A/C. I found a thermometer I had in the car, and turned the A/C back on. After about 30 seconds (a minute?), the temp dropped no further than 77.5F, which I knew could not be right. So, I shut it off, and decided moments later to turn it on one more time. At this point, I had my driver's side door opened, my left foot on the ground outside of the car, and moments later...BOOOOOM! I felt something (Freon gas? a rock? a part of the compressor?) hit me in the leg. and then I saw fumes rise up from the engine bay (I had the hood up). So, after being stunned momentarily, I decided to check on what happened. There was green goo all over in the bottom front driver's side area of the engine bay, and then I knew...it was likely the compressor. You can see the immediate aftermath in the pictures below. Later, I checked underneath to make sure it wasn't the new hose; nope, it was intact.

After discussing with my mechanic (I was level-headed; after all it's a 35 year-old car), he believes it could have been a plugged condenser. Now that I'm looking at a condenser and an aux fan on top of what I've spent, I'm ready to punt and move to the Sanden. Might as well go modern if I'm going to have a reliable system. But that's for next year.

Of note, my mechanic says he'll refund me; that of course is good. His diagnosis? The compressor's case blew; you can still see a gasket hanging on the outside of the unit. However, when he mentioned to me that the system didn't have a high side port (it does, which he found after the blowout) and that there are no real pressure checks in the system, this may be a job for someone more familiar with these cars. I'm glad no one was hurt; he or anyone from his crew could have been injured rather severely, I believe. He also stated those compressors are supposed to have some kind of pressure relief valve, but it apparently didn't work or this one did not have one.

Sounds very familiar...happened to me not that long agi
http://www.peachparts.com/shopforum/diesel-discussion/379496-compressor-failed-spectacularly.html
Out of curiosity, can you check the 19mm bolts that hold the compressor to its bracket are tight, please?

I did not realize your situation was almost exactly as mine (I've read your thread previously, too), until you mentioning it now. Wow! Lucky no one was hurt in either case.

I see you've went the Sanden route. I may do the complete Klima kit that I've seen online, but I've had enough of dealing with major headaches in regards to my car for this year. I can get by without; have all summer to this point. That kit, plus a new condenser and aux fan would run around $950, parts only from Klima Design World. Vintage Air has complete heating/AC systems for a little more than that, but not much; might be a good idea to start with a brand new "climate control" system. Or, how about this for $466? Doesn't look to be a complete system, but I'll bet the total would be less than the $950 for the Klima/Sanden complete system overhaul.

http://rover.ebay.com/ar/1/711-53200...pY%26vxp%3DmtrVintage Air Universal Gen II Super Cooler Heat Defrost Air Conditioning System | eBay


RE the 19mm bolts: I can check 'em, but I doubt they were an issue; everything looked in place and tight after the blowout.

EDIT: Upon further review, the Vintage Air idea looks awesome, but since they're selling the Sanden compressors for their kits, you'd be monkeying with that...PLUS installing the new Vintage Air kit. Plus side to the Vintage Air? Total bypass of all existing climate control (heat and air now controlled by new unit), plus adaptation into your existing ductwork---no vacuum control necessary.

Your R4 looks just like the photo in #10 of the linked thread of post #2. It appears the steel outer shell slid forward, which let the O-ring extrude. The only thing that holds that shell in place is a little tab that folds down against the aluminum inner body. You could conceivably fix it in-place by just reinstalling the O-ring (or a new one) in the groove, sliding the shell back, and securing it. Perhaps the lock tab broke off and the rebuilder's didn't weld on a new one.

There is a place for a pressure-relief valve, which might have been installed in some GM apps, but in ours there is just a plug w/ snap-ring there. At least, that is what I recall from past posts here.

I doubt anyone would have been hurt had they been working in the engine bay, unless it scared them to bump their head. Worst would have been a face-full of refrigerant oil.

The high-pressure port is well hidden on the tube that runs up behind the alternator. But, the factory procedure is to fill a certain weight of refrigerant (3 cans, I recall), so unlikely they would have over-filled it. Seems there might be some less than ready-for-prime-time rebuilt R4's in the supply chain, perhaps traceable to some Billy-Bob assembler who doesn't understand them.

I just re-installed my R4 (after removing every component in the AC system other than the evaporator for leak testing). I looked at the install carefully and come to the conclusion that the only thing that keeps the casing of the R4 from sliding off towards the clutch end of the compressor is the bent sheet metal tab on the casing, not the mounting bolts/ brackets or anything else.

So the big question is what caused your's and Demothen's to explode? They are both brand new R4's, not rebuilt's. Is it a quality issue or operator install error?

The fact that your mechanic says there is no high side service port says he does not know much about the AC system in your Mercedes.

Can you take off the compressor manifold (13 and 15 mm wrench) and take some pics of the parts? There is an aluminum insert in the suction side sealing step washer (the bigger diameter of the 2 tubes) that must be installed. He could have dropped it and not even know about its existence when it was first removed.

The aluminum insert provides support of the rubber seal on the step washer so it is not squished out. On the discharge side, the insert is built into the manifold. On the suction side, it is a free floating piece that can be a puzzle to install for those not familiar with it. Without the suction insert, it is possible for the step washer to leak and and suck in air.

Regarding your cut hose, was it actually leaking refrigerant/ oil? Those Mercedes hoses are thick and tough, a surface cut likely will not cause a leak and still be serviceable. On the suction side, the hose sees pressures of 15 to 30 psi running, 60 to 80 psi when off. On the discharge side, the hose sees 150 to 250 psi running and 60 to 80 psi off.

What I found with pressure testing my AC hoses (all original) in my 85 was that none of them leaked. The only parts I found to have issues were the black o-rings, they must be the original Neoprene o-rings, which are in sad shape ....... some did not look like 0-rings anymore. There were some green o-rings (HNBR) in the TXV and receiver/ dryer which are in good condition, they were installed when the system was converted to R134a.

I have quite a few old AC hoses I pulled off an 83 240D and 81 300D. I will pressure test those when I am finished with the AC in my 85 and see if any of them leak.

After more thought, Funola, I agree with you - the R4 is only held together by that one tab. Mine was a new unit, not a rebuilt, though I don't recall the brand. I ended up returning it. I still have the original unit that was with the car when I bought it (squealed really loud) - I'm thinking about opening it up just to see what it looks like inside, since I don't need it as a core. I'd offer to ship it to someone to use it as a core, but I'm pretty sure shipping will be way more than it's worth as a core.

I don't know about the vintage air system. Looks like you will need a control panel, condenser, aux fan (not mandatory, but if you switch to a PF condenser, I would recommend an aftermarket one) compressor & brackets, and hoses, drier, and possibly sensors? When I looked at their full kits I remember them being roughly 2k$. I have spent roughly that amount for my new system, which includes a sanden & hardware, all new hoses, PF condenser, aux fan, and new evaporator + used housing to fit it (see my other thread on the complete rebuild). But with this I get to keep my interior controls stock.
Its your car though.
I should have a new evap housing this week, but am in the middle of another project that is on a time rush. Once I get it in and have time I will take some measurements of both housing options and lots of side by side pictures so you can get an idea what space is available behind the dash.

Are you sure the squealing was not a loose belt? Definitely open it up and have a look to see if you can determine the cause of the squealing. Without the special tool (a press made for the job), I'd use a hammer and punch and tap the casing off by tapping alternating opposing 180 deg on the case.

Pretty sure the belt was not the problem. Hard to explain the noise, it wasn't quite a belt squeal, and it was intermittent only - but it was really unpleasant.

Electromagnetic clutch slipping ?

That was my guess. I was also having problems charging the system (insufficient siphoning from the can - later attributed to clogs in the system) so I decided to replace with an R4 - which then failed in a similar fashion to this thread, so now I am in the process of rebuilding everything and upgrading to a sanden.

Well, from the pic below, something wasn't hooked up. Have no idea why the wires in the pic are simply taped up, or what they are for. Perhaps some non-installed safety valve?

Regarding the explosion and the danger (or non thereof), all I can say is this: it was very similar to a blown tire---quite frightening. Whether it would have hurt someone or not, I don't know, but I believe the simple discharge of gas may very well have done so. Remember, something (I don't know what) hit me in the left leg just above the ankle as I had my foot on the ground outside of the car on the driver's side while seated. It hurt! So, just imagine what that could have done had someone had their face poking around in there. If you Google "blown AC compressor", you'll see photos of ones that physically blew shrapnel shots out of said compressor (the very first one I see is from an SHO---not good). Also, see the vid below:

https://www.youtube.com/watch?v=J7MfYy2U0Zc

Auxiliary fan wiring. Should be a temperature sensor screwed into the receiver/dryer right there.

Just out of curiosity, was the original compressor "bad" because it was seized?

-Rog

Did you try spraying brake cleaner into the clutch gap to degrease it? My clutch was smoking and cutting in and out a while back but did not squeal or make any noise. Upon inspection, it was all oily on the outside from a previous bad valve cover oil leak (not from refrigerant leak). I sprayed the gap with brake clean = no more smoke or cutting in / out of the clutch.

If the brake cleaner question was oriented at me, no I didn't. It costs 50$ or so each time I fill up the system (recovery cost, r134a, receiver drier, o rings) - vs ~200$ for the new r4 compressor. I tend to move towards replacing anything suspect instead of wasting time & money and hoping that the old parts will work - hence my 100% complete system rebuild - well, 99% rebuild. I will have exactly two original components in the refrigerant loop, both of the metal fittings that connect to the TXV.

It was directed at you. So you did not do any testing or diagnosis to learn what caused the squeal? I fixed the smoking clutch with 1/10 can of brake clean. Are you saying I should have replaced the R4 instead?

I'm saying I had a system that wouldn't take a charge and was making horrible noises. I had absolutely no idea when the compressor had been replaced (if ever). The only way I could diagnose the horrible noises would be to charge the system to reproduce them. I made the call to replace the compressor (Which ultimately didn't go so well, since the replacement failed even worse) because it made financial and labor-cost sense to me. In my case, it made sense to replace the unknown part with a hopefully good part. That didn't work so well, but there's no way I could have known that the new compressor would fail so rapidly (I've since returned that compressor). I've spent a lot of time repairing parts on this car to save money vs buying new parts, including parts that are not supposed to be repairable, and really I just wanted to get the car back on the road in a timely fashion (any time I'm not driving the car, it's wasting money since I keep it insured).

I'm definitely not saying you should or should not have done anything. In fact, I admire that you've gone through so much work to test every component of your system, and I'm looking forward to comparing the results of my "replace ALL the things" methodology vs your "test everything" methodology.

Returning a part damaged by improper instillation is unethical.

Over on tech section, there is a guy that returns properly working parts once a year under the lifetime warranty. This is unethical too.


In another thread:
http://www.peachparts.com/shopforum/diesel-discussion/379496-compressor-failed-spectacularly-2.html

Post 22


07-25-2016, 06:23 PM
Demothen is offline
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Join Date: Nov 2015
Posts: 413
Well, looks like this was my fault after all. Apparently I forgot to do a final torque on at least two the compressor bracket bolts, or they loosened on their own. Most likely I forgot to torque them. I am not going to return the compressor now since this was clearly my fault.

And this is why I used touch up paint to mark suspension bolts after torqueing them. Plus it easily indicates if they have backed out for later inspections.

After actually pulling the part, it was clear that not tightening those bolts was not responsible for this. See also: this thread. Furthermore, I told the parts store exacty what had happened.

For me, the testing/ diagnosing of the components is to gain knowledge. By just replacing the entire system, you haven't learned anything and will make the same mistake(s) next time.

Heh. I have learned a lot like "tighten ALL the bolts" and "replace anything that looks faulty"... :)
I do plan on pulling the original r4 apart once I get some time. Right now I am focused on getting the car back on the road ASAP

Since it got buried...

I ask because if it was, that could give a clue as to why the new one popped.

-Rog

Who are you asking, Rog--me or Demothen? In my case, when I asked my mechanic to look for leaks and recharge the system, he said the original (bad) compressor was "puking" fluid (a/c oil/refrigerant) out of the front of it...whatever that means.

http://www.peachparts.com/shopforum/diesel-discussion/380380-r12-vent-temp-85-300d-38-5f-%40-87f-ambient.html

Edit: Compared to what you have gone through, I think I did a lot less work, spent a lot less money and learned a lot more in the process.

And mine was not seized, but was making a squealing noise and not siphoning from the r134a can during the charge. I also later noticed that it seemed to have two types of oil that didn't mix together in it. The not siphoning problem was probably actually caused by some clogs in my lines. The squealing was probably grease or excessive wear on the clutch, or possibly bad bearings.

Refrigerant does not get "siphoned" in from my observations. If you watch your manifold gauges while charging, the suction side pressure in the system is 30 to 50 psi positive pressure, not a vacuum. The static pressure in the R134a can is around 70 to 80 psi depending on outside temperature. The refrigerant is slowly pushed into the system because it is at a higher pressure, not siphoned in, that could take a long time... like 20 minutes or more. If you invert the can and let the refrigerant trickle in as a liquid a little at a time, you can speed up the charging process.

I was having a mechanic help me do the charge at the time. He said it was not behaving normally, and that it would not take the charge. He couldnt get much if any of the second can in. Siphoning is a bad term for it, but its what came to mind.

Did he increase the engine rpm to speed up the process? When the engine is revved, suction side pressure drops, refrigerant intake speeds up.

Yep - well, actually I worked the throttle.
It charged much easier without the clogs in the system and with the new r4.