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 Compressor Noise. Is it Compressor? By Paul Weissler - MACS Technical Correspondent-

We’ve been hearing a lot of complaints about remans being noisier than brand–new OE compressors.

Shops have said they’ve gone through isolating refrigerant lines with rubber, retightening brackets, replacing lines with mufflers, and eventually came down to getting a brand-new OE compressor-and reporting that it solved the problem.

Sure, it happens occasionally sensitive.  Perhaps the reman was made for a different application and although it physically fits, there is some imperceptible difference (the OE specific one for a particular vehicle may have an internal muffler, for example}.  Or the reman was installed with an adapter bracket,  and sometimes they just don’t restrain the compressor as well.  This problem becomes particularly noticeable on an older car where the engine mounts may be worn (so the engine is shaking a bit), or the engine itself is worn or in need of a tune up (so it isn’t running as smoothly}.

But we also hear of a lot of noise complaints with remans that “just seem to go away” after an evac and recharge.  With those we suspect that air in the refrigerant or an improper charge was responsible.

Or the brand-new compressor came with a fill of oil, whereas the reman was shipped dry, and no oil was added.  So the reman had to run on its assembly lubricant and suffered premature wear.  Or when the brand-new compressor was installed. The shop went the extra mile and replaced the old condenser with a new high-performance model.  That eliminated the real cause of the noise –a restricted condenser raising discharge side pressures. The list of possibilities goes on, but you get the idea.

We would like to point out an interesting item: among the complaints we hear about so-called remans actually are about brand-new compressors.  The new Sanden or Zexel, which are used without incident as original equipment, probably also are as popular as adapted replacements as any compressors on the market.  They’re well made pumps that are sold in such high volume that large distributors can buy and sell them (with adapter brackets) at attractive prices.  There have been a few complaints about these new compressors being noisy, and we know they’re as unlikely to be defective as any other new ones.  In the majority of cases, a adapter kit works fine, so long as it’s properly tightened down and the refrigerant lines are well-restrained.This is particularly important with a retrofit, where the higher pressures of HFC-134a produce noise waves.  But there are exceptions and alerting a customer to the possibility is something you should do.

A recent report by a technician with a 1989 BMW 5-series is an example (virtually all BMWs of that year had Bosch compressors as OE).  He tried a Sanden and adapter kit to replace the failed Bosch compressor, and the customer found the A/C compressor noise objectionable.  The tech had to get the OE compressor, a Bosch, to satisfy the customer.  People with BMWs may be more willing to spend the extra money for the quiet.  But basically there is no reason to believe that a Bosch compressor is inherently any quieter than a Sanden.  The engines and their mountings and the compressor bosses are validated for quiet as part of the OE engineering processes.  If necessary the mountings and bosses are tuned and shaped for the compressors the OE manufacturer chooses, and alternatives aren’t always as smooth in some particular cases.

If you install an adapter kit, we’d urge you to make absolutely sure that the compressor pulley is in perfect alignment with the other belt-driven accessories—put a straight edge across the pulleys.  You may have to shim to achieve alignment, and you certainly should use thread-locking compound and a torque wrench on the mounting bolts.  Some brackets are not a perfect fit – you may have to file to get them to fit properly. And good fit is important for noise control.  If a bracket doesn’t fit in all the way so it’s flush with a mating surface, misalignment is likely.

If you’re re-using the clutch (or took a salvage one off the shelf) be aware that it may be the source of noise.  You may think you’ve pinpointed a noise to somewhere within a compressor using a stethoscope, but noise is easily transmitted and you can be deceived.

We also get a lot of reports about how happy shops were with their adapted installation of new Sandens and Zexels, and how delighted the customers were to save several hundreds of dollars.

The choice is yours – OE new, aftermarket new (bolt up “clones”), remanufactured and adapted new.  Evaluate your customer, his/her car and the $$$$ available.  If a customer is very price – sensitive, he/she should be willing to accept some possible noise to save the money – and when advised in advance is more likely to accept the results.


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