1999 C280 AC System Flush Process - Mercedes-Benz Forum
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post #1 of 22 (permalink) Old 05-23-2019, 09:55 PM Thread Starter
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1999 C280 AC System Flush Process

Hi,

I am getting ready to RR the AC Compressor. I found the Mercedes document for it but it doesn't talk about flushing at all.
Does this car's AC system not need flushing even when I disconnect the old compressor and see contaminant? What is the proper process to flush this car? Can someone please point me to this document from Mercedes? And also links please if there's any related thread for this job.

Thank you so much and a great weekend!
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post #2 of 22 (permalink) Old 05-24-2019, 10:30 AM
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Last time I "flushed" it my local shop did a vacuum evacuation.
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post #3 of 22 (permalink) Old 05-24-2019, 11:19 AM Thread Starter
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Originally Posted by MB-W202 View Post
Last time I "flushed" it my local shop did a vacuum evacuation.
ok, so how did you flush it before you had your shop evacuate it?
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post #4 of 22 (permalink) Old 05-24-2019, 12:48 PM Thread Starter
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So here's the process I am supposed to follow to replace the AC compressor -
1) Put the front of the car on jack stands and put chokes on the rear tires.
2) Unbolt and remove the suction line and pressure line from the AC compressor. Plug clean rag at the open end of each line right after disconnecting to prevent dust and moisture getting in.
3) Unbolt and remove the AC compressor making sure you don't tilt it during the process or else you'll spill oil from the open ports where the lines were connected.
4) After removing and w/o delay pour the oil from the compressor into a container. If the oil color is dark and dirty and/or you see debris, it means your AC system has contaminants.
5) If no contaminants, then you do not need to flush your AC lines and can proceed to install the new AC compressor.
6) If your system has contaminants, you would need to flush and dry out the AC lines thoroughly and replace the expansion valve.
7) Install new compressor and connect back the suction line and pressure line.
8) Replace the old receiver/dryer with a new one.
9) Evacuate the system thoroughly, checking the pressure gauges. Make sure the system holds the pressure which will indicate there is no leak anywhere.
10) Now you can charge the appropriate amount of R134A.
11) Test with temp gauge you are getting the correct temp at the outlets.

There are more details and specs along the way and I will include all that here after I am done replacing the AC compressor.

Now my problem is although I am clear on every other step, I am NOT on step 6) - which is how to perform the flushing w/o affecting any other part in the system like the evaporator, condenser, etc. I do have a new expansion valve and know how to replace it. I also have the flushing chemical liquid and have arranged for the flush gun bottle and air compressor to drive it.

So can anyone share or point out the appropriate flushing process please? I would so greatly appreciate it! My thoughts are it must be known by many since AC Compressor RR is quite common....or am I wrong???

Note: I'am learning from shops they mostly do not do flushing but just suck out debris and dirty oil with their evacuation machine. Is that perfectly fine or a short cut not recommended?
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post #5 of 22 (permalink) Old 05-27-2019, 11:12 PM
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Great question! It used to be that flushing the AC system was an important and effective step to ensure longevity of the new parts, and typically that was done with a flush solution and then nitrogen was used to dry the insides of all the parts. But that’s no longer appropriate for modern cars. Scotty Kilmer shows us why:

https://youtu.be/U0O1mcnwjZs

My standard DIY process now is to replace the o-rings on all fittings, the compressor, the condenser, and the receiver/drier. Then I pull a vacuum on the system and fill it with refrigerant and I also make sure to use a small bottle of pre-mixed compressor oil/refrigerant, making sure to test the temperature of the air coming out of the vents is at spec.

A shop with a good AC machine can flush the system with refrigerant to collect any remaining impurities and many of those machines also have the ability to separate compressor oil from refrigerant, but the machines are expensive and that’s why shops charge big money to do the job.

Since we’re talking about a 20-year old car, my DIY method should serve you quite well and keep some money in your pocket.
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post #6 of 22 (permalink) Old 05-28-2019, 12:00 PM
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I'm going to say that 90% of shops do not do a flush of the system. But on the other hand, most aftermarket compressor companies will not honor the warranty on the compressor if you do not flush the system.

I think determining on whether to flush or not depends on why you are changing it to begin with. If it is a matter of the clutch failing, or the seals leaking on the compressor, I would say a flush is unnecessary. If the compressor failed internally(like locked up) then I would recommend flushing all lines, the evaporator, and replace the expansion valve and the condenser, and the dryer.

After that it is also important to put the correct amount of oil in the system, which depends on whether you flushed the system or not. If you flushed it, you need to put the manufacturers recommended amount of oil in the system. If you did not, you only need to put in what the old compressor had in it. Which means, you have to pour the old oil out of the old system and measure it, then pour the new oil out of the new compressor and save it, then put back the amount that you poured out of the old compressor. Then you should do no less than a 30-60 minute vacuum, then charge.

Hope that makes sense.

Also just a diy tip; when putting the ac fittings back together, replace the orings, and lubricate them with some ac system oil. This will keep them from tearing when you put them together, and the ac oil will not contaminate the system vs using some other lube.
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post #7 of 22 (permalink) Old 05-28-2019, 12:10 PM
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btw to answer your original question, it sounds like you have what you need coming as far as the flush. It is just a matter of removing the lines on each end of what you want to flush, put the can of flush up to the line and squeeze the trigger, and the solution should fly out the other end, so do it somewhere where its ok to make a mess. As said, you will want to make sure the line is dry afterwards( I think just blowing some air in the line afterwards til the air comes out dry is sufficient). You may have to take some extra lines loose to gain access, and I don't know if I would waste my time flushing the condenser, if you have contaminants in it, the flush is probably not going to get all of it, and you may have a hard time getting all the flush out of it anyway. Replacement would be best, and they are not that expensive(try 1800 radiator) Any water left in the system should get evaporated and sucked out by the vacuum process, but this is why you do an extended vacuum; 15 minutes is not enough. An hour would be best.
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post #8 of 22 (permalink) Old 05-29-2019, 11:00 PM Thread Starter
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Great input guys - thanks so much! really appreciate it!

How about I have any small amount freon that may still be in my AC system recovered, then evacuate and see if the system holds the vacuum for an hour (or longer) as indicated by the gauges? Would this be a good test to make sure there are no leaks anywhere in the system or am I perhaps missing something here? Then I would disconnect the compressor and determine from the oil whether or not the system needs flushing - and go from there.

To give you a quick background, the AC stopped blowing cold air back in August 2010 (yes that long ago!). Took it to the dealership within a couple of days and they recharged it with dye to detect the leak. The recharge lasted for until May 2012, when the dealership found the leak was on the suction hose (part# 112-13-56) that runs between the compressor and the separation point where it joins another suction line from the exp valve.
In Sep 2012, I had an Indy replace the the suction hose and receiver drier (both with new Genuine Mercedes parts) at my place. Two minutes into charging the first can of freon, we heard the compressor make a metallic noise. It was then that I recalled hearing that same noise may be just a couple of times for about a quick few seconds each time. Anyway did not operate the climate control at all (not even the ventilation or heat!) from that day!
Bought new OE Denso compressor in Dec 2012 from the distributor at a great price! Also have a new OE Hansa Receiver Drier and Egelhof Exp Valve.
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post #9 of 22 (permalink) Old 05-30-2019, 06:38 AM
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My only concern with what you said is, what caused the noise? Was it the clutch or the compressor? If it was compressor, I'd do the flush. But I agree in that looking at the oil in the compressor, you will likely see metal shavings when you drain it.

If you can, let the vacuum sit overnight, then check the guages in the morning. If they havent moved, then the only place you could have a leak would be at the schrader valves themselves, or you dont have a leak.
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post #10 of 22 (permalink) Old 05-31-2019, 02:04 PM Thread Starter
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hi georgebuhr,

Slightly confused here...
Schrader valves are the valves on the gauge manifold that you connect to the high and low AC ports on the car right?
I had no idea they could leak - and is it okay if they do?
Also why would any leak there not cause the gauges to move? or is the leak too small to be detected?

BTW, as you may have figured out, the sole purpose of trying to detect system leak this way is it will not cause any or further damage to the system and that too before replacing any component in the system!
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