Compressor & Condenser Installed/Knocking Sound?

[fuzzyturnip]

Hi Legacy Fans, We love our 1993 - it's at 220K and running strong!

The a/c system went out at the end of summer here in Las Vegas last year. We had a compressor and condenser installed. She's blowing cold! Except now we've noticed a knocking sound which appears to trigger only when the air conditioner is turned on (and even so, only once in a while, not all the time) and appears to subside when the car is neutral and the RPMs are revved up!

We were able to capture the noise and the engine while it was happening with our iPhone on video. If you've got guesses as to what the heck this could be, we're all ears!

http://www.youtube.com/watch?v=90W-qB7_rQA

Thanks fellow Legacy owners - our cars are truly the definition of a daily driver. We've never had a car be so good to us with regular maintenance and minor upkeep. Gotta love the Subaru Legacy!!

-John & Sherry in scorching hot Las Vegas, Nevada

[Legacy777]

Welcome to the BBS.

The knocking is coming from the compressor and is really an indicator that the compressor will fail at some time. I say it will fail at some time, because it may be next month, or it may be a year or more away. The compressor design is such that they can't be rebuilt and over time if they are not used regularly can fail.

From looking at the video it appears the system may have been converted to 134a. Can you provide any details as to what was done when they performed the AC work. Was the compressor brand new or a used compressor? Do you know the type of oil that was used?

I've been through about 4 compressors before buying a brand new one. The old R12 AC systems can be converted to 134a, but from my experience they don't get converted properly and tend to have problems after a while.

Any additional information you can provide would be helpful.

[fuzzyturnip]

Hi Josh,

You're a wealth of knowledge. We figured it was the compressor and you're right, we're on our third one from the original. The original one finally died after 17 years!! The second one lasted exactly one summer. To be honest, it didn't look very good to begin with - the fact that it got through us the desert dry Las Vegas summer was a miracle. This last one, a Calsonic, was just installed a couple weeks ago. It was a used compressor purchased from eBay. I suspect it's dying or like you said, there's too much/too little coolant/freon in there?

Does it hurt the engine or other components of the ac system to run a knocking compressor? It only knocks some of the time - I suspect when the clutch engages or when it's very hot out, maybe??

Should we just run this compressor until it dies or switch it out right away?

By the way, you are right about the conversion, not sure what kind of oil was used.

If you've got a recommendation on where to get a new compressor - a place you've had success with and you like, we're all ears!

Thanks Josh. The Legacy may not be the fanciest car around but we swear by it's reliability.

-John and Sherry in Las Vegas, NV

[Legacy777]

It will not hurt the engine to run the compressor until it dies. I would suggest just running it until it croaks.

If you don't want to mess with the AC again for a while, I'd suggest getting a new compressor from the Subaru dealer. You can use one of the online dealers such as www.subarugenuineparts.com A new compressor is about $400 or so. I don't know if you're going to be able to find a "new" compressor anywhere else. Any of the ones that you find that are listed as "rebuilt" are not going to last due to the compressor design. They just can't be rebuilt.

I'm not sure exactly why these compressors don't last, but I would guess it's due to lack of lubrication and not being used throughout the winter months. It's a good idea to run the AC at least once a month to keep oil circulated and the compressor lubricated.

As for the conversion, check out this thread.

http://bbs.legacycentral.org/viewtopic.php?f=11&t=1083

It's got a lot of details regarding converting to 134a. I recommend using PAG 100 oil, and replacing the receiver drier. It would be good to flush the system, especially if you've had a compressor fail. It can send metal shavings into the system and muck it up and cause premature failure of the next compressor. Some of the AC guys call it black death when the compressor fails. It's just shoots a bunch of junk into the system.

Hope that helps.

[Omega79]

Most rebuilt units are going to cost just about as much as a new one unless you have a hookup, so you're better off with that like Josh says. I have a hookup for a Ranshu dealer, which was cheaper for me, but I still have to worry about whether it will last. However it does have a good warranty and I can do the work myself.