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A joke? BMW AC compressor failure can cause engine chain problem?


I have a 2007 BMW 328xi with only 46000 miles. About three weeks ago, I heard some pumping noise under the hood so I drove the car to a repair shop for esitmation. I was told that the AC compressor stopped working. When I drove out of the repair shop about 5 miles, the car stopped running and was towed back to that repair store. After the new AC compressor was installed (cost is $1500), the car still could not be started. It was then towed to dealership. Now I was told that the AC compressor failure caused engine chain problem, to fix it, another $4100. Does it make sense? How AC problem can cause engine problem? Your help is very much appreciated!

With these $$ at stake I’d post this on one of the BMW 3-series forums, you’ll have more luck finding folks with that specific experience.

Your AC compressor is driven by the crankshaft. So is the timing chain. If an AC compressor were to suddenly seize while the engine was running, say at 3,000 rpm, it would typically pop its drive belt (in modern cars that’s often a serpentine belt) before stopping the crankshaft completely, but I suppose it is possible for it to stop the crankshaft and the chain jump a tooth…if there’s already wear in the timing chain system.

I posted on bimmerfest forum too. Just want to get more broad opinions and raise the awareness for bad custom service on BMW. This defintiely will be my last BMW!

As mountainbike explained well, the common link is the crankshaft.

I’m only going to add that at 5 yrs old and only 46K miles, this is an absolutely absurd thing to have happen. I’d imagine its out of warranty, but this is so screwy that if it turns out that the diagnosis is correct I’d be making a lot of noise with BMW.

I have contacted BMW NA, they did not want to offer any help. The custom service representative told me that she will file a claim for me but can not gurantee that anyone from BMW NA will call me back. What a joke! I do not know what other noise I can make, maybe post on their facebook page. Anyway, so disappointed!

The job of corporate customer service offices is to basically cool you out while they deflect you from really getting anywhere. One way they do that is by making it complicated and making you believe that you won’t get anywhere. (Always smiling!) You’re supposed to decide its hopeless and not worth the trouble and then go away.

Most of the time there is an actual corporeal person you can get a chat with - often a regional manager. You can probably get farther that way.

You still might not get anywhere. But I tend to get a little tenacious when I feel like I’m stuck holding someone else’s bag.

I talked to assistant custom manager and was told that my case can only be escalated once, which means from a custom to her. So I have reached the ceiling already. I have asked how their decision were made, she said she can only tell me that the decision was made but will not disclose the rational behind it. It is the worst custom service I have had so far.

Some more of the story might help but I would say that’s it possible for a timing chain problem to occur if the engine suddenly slammed to a halt due to compressor seizure; especially if there were possible problems with the chain anyway.

Some questions and points for discussion might be:
Did you buy the car brand new?
Did the first shop offer a repair and you declined that repair; followed by driving off with a known problem?
How often, both mileage and time-wise, do you have the engine oil changed?

The car is going on 6 years old and only has 46k miles on it. This could point to very light use and depending on the oil change regimen the engine could be a prime candidate for oil sludging problems. One of the things most affected by oil sludge is a timing chain and tensioners.

Why are folks saying the a/c compressor is connected to the crankshaft? The photos I’ve found show it driven by a belt, as one would expect. In that case I don’t understand how a seized compressor would affect the engine. Break the belt, maybe, but that hasn’t been mentioned.

I had a Nissan Sentra towed in to me once with a frozen engine and the owner fully prepared and expecting to pay for a new engine; and this was on a purchased from new, extremely well maintained, low miles car with only 50k miles showing.
The cause was a frozen idler pulley bearing for the A/C compressor belt. The engine in this case slammed to a halt as they backed out of their drive and came to a stop before shifting into a forward gear and at idle.

If this happened with elevated RPMS and at speed I’d say that it’s possible that rotating mass could have caused a problem.
In this particular case the belt did not break nor did it even slip but it locked that motor down like it was welded.

And what other than the crankshaft do you suspect drives that belt? Texas, I know you know how this stuff is put together. Your question puzzles me.

Actually, if you reread mu first post you’ll find that I did mention the belt. I also said that I would normally expect it to break the belt. I also acknowledged that it might be possible of there was already a lot of wear in the timing chain system.

Tough day, Texases?

Well, TSMB, I just made a jump, that there was some direct connection assumed. Now that I’m back to the real situation, I cannot understand how a frozen compressor could cause any engine-related problem, unless something in the engine was near failure. Wouldn’t a belt break first?

Generally. But that goes to the question of which is stronger, a belt in good repair or a worn chain? One weak link in the chain can make the chaiin more prone to fail than the belt.

I admit, the chain breaking instead of the belt us a stretch (pardon the pun). But I’ve seen stranger things.

I’m thinking the all important details are not going to be filled in by the OP. It would be interesting to know if the compressor blew up, compressor clutch seized, or whatever.

What about the possibility that the original diagnosis was dead wrong and there was nothing wrong with the compressor at all? Maybe the real problem was an engine fault waiting to finish itself off although the pumping noise as it’s described is kind of vague.

And how did the dealer, who I assume has not seen the allegedly damaged compressor, determine that a bad compressor caused the problem?
There’s a lot of questions on this one including why would a shop run up a 1500 dollar tab on a compressor after seeing a car towed in? (Again, assuming the compressor was not blown up ro seized.)

I’m with Texases on this one . . . belt should have snapped before a timing chain. You would think that internal engine components like the chain would be engineered to withstand more than the force of an (assumed) seized AC compressor and I would expect the belt to snap way before the chain. One thing though . . . BMWs are expensive once they break. BMW . . . break my wallet? Rocketman

No one here is assuming the timing chain snapped. IF this whole story is as told, and the OP started out with an AC compressor problem and ended up with a car that wouldn’t run, there is some possibility that the chain main have jumped time. Should the accessory belt have broken? Sure. Does that mean it always will? Never say never - or always. Look at ok4450’s story about a Nissan above. If your engine is cooking along with the AC compressor running, and it seizes, I don’t care what else you want to say. The crankshaft is going to take a jolt.

Of course, at the moment we’re relying on a “story” that came out of a dealer & then was retold by the car owner. So all of this is predicated on trusting that dealer’s diagnosis. But this whole series of events is not impossible.

We don’t have any way of knowing. All we have at this end is the OP’s statement that he/she was told that the AC compressor caused an engine chain problem and the question: “is this possible”. IMHO yes, it is possible. Not probable, but possible.

Bear in mind also that a “chain problem” could also mean a chain that slipped a few cogs. I’m not sure how BMW puts their system together, but if it’s typical it’ll have two guides, one also serving as a tensioner. If those are worn, and the sprockets are worn, it is not inconceivable that if the crank were suddenly stopped by the belt the inertia of the flywheel combined with the operating cylinders could cause the chain to jump a few cogs.

Again, we have no way of knowing. All we have is what the OP has given us.

It could also be that this engine has variable valve timing, and the shock to the cam chain damaged something in that mechanism.

Excellent point. A tip of the hat to you.