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  #1  
Old 09-20-2016, 07:33 PM
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Vacuum flush AC system

I had to flush the AC system again in my 85 300D due to a leak on the case o-ring on the R4 compressor. Last flush, I used a solenoid pump to cycle mineral spirit through various parts of the system. This time I used vacuum to suck in the flush agent into the entire system. It works great! Even less work and mess than using a solenoid pump.

Here's the adapters needed. On right are adapters for the evaporator, made from a TXV. On the left is the adapter for the manifold, which bypasses the compressor. It's made from an old manifold assembly.










Connections to the receiver dryer hoses, where the flush is introduced and removed.






Evacuating the system with a vacuum pump. Note the ball valve on the input hose which is connected to the vacuum pump. A plug is in the output hose. It takes running the vacuum pump about a minute to create enough vacuum.






The input hose is put into the flush solvent and the ball valve is opened. This video https://www.youtube.com/watch?v=T2cdi_nHK8s was taken towards the end of suction when the system is almost full. It took about 30 seconds to fill the system completely, which includes all hoses, evaporator and condenser.






This is what the mix of solvent and PAO 68 oil with dye looks like after being pumped out with compress air. The solvent was Kleen Strip denatured alcohol which is a mix of methanol and ethanol. It has a really low flash point. The rag used to soak up the solvent blown out with high pressure compressed air is completely dry after 5 minutes in the sun. I flushed twice, each time used about 3/4 of a gallon. The Kleen Strip denatured alcohol was $12 /gallon at the local hardware/paint store but $17 @ Home Depot.


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Last edited by funola; 09-21-2016 at 09:38 AM.
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  #2  
Old 09-20-2016, 08:09 PM
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Nice work & nice photos! Great adapters. Very creative!!

As a cleaning solvent/dehumidifier you could try Isopropyl alcohol 91% (about $5/gal). Works great, absorbs water very well, cooks off easily under vacuum, & leaves no residue. Learned that from an old grey beard HVAC tech 40+ years ago. Make sure you change the oil in the vac pump after using solvents. Some pros change out the vac pump oil after each job. Saves the pump. Nice work & a tip 'o' the hat to you, sir!
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Old 09-20-2016, 08:18 PM
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Thanks for the kind words CF. The vacuum pump was used to draw a vacuum to suck the solvent in only, not to suck it out. I did not want to contaminate the vacuum pump oil. I used plenty of compressed air to make sure all the solvent is blown out before evacuation for charging with refrigerant. That is easy to tell since Methanol has such a strong odor. I blew compressed air in till what comes out has no odor before connecting the vacuum pump to the system.

Where do you get 91% Isopropol alcohol for $5/ gal? At Walgreens they are $5 / pint.
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83 300 D turbo 297K runs great. SOLD!
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Old 09-22-2016, 12:11 PM
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Impressive! You might have to rent out those adapters and hoses. You've created.
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Old 09-23-2016, 10:03 AM
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Originally Posted by DeliveryValve View Post
Impressive! You might have to rent out those adapters and hoses. You've created.
Thanks! I'll have to think about that one, my first (and only) time renting a tool out by mail was not a pleasant one.
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Old 09-23-2016, 10:20 AM
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This is what the entire system on a W123 AC holds (minus the compressor and rcv/dryer). I did spill about 1/4 of a pint when it over flowed out of the bottle on the left. Good that I had secondary containment! Next time I will use a gallon size catch can.

I've read that parallel flow condensers cannot be flushed. IMO, I think drawing the flush agent in by vacuum like I have done should work very well with parallel flow condensers. It will fill the P flow condenser completely with flush agent and thin the oil in it to allow it to be blown out easily. Should work well as long as the compressor has not grenaded and produced FOD or black death.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
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  #7  
Old 09-25-2016, 04:12 PM
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That looks like some tasty OJ in those containers
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  #8  
Old 09-25-2016, 07:36 PM
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Originally Posted by Cloudsurfer View Post
That looks like some tasty OJ in those containers
I thought the same. The flush is water clear but the dye in the oil made it yummy looking. If you drink it you die.
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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
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Old 09-25-2016, 07:58 PM
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There is never enough time to do it right, but there is always time to do it over. I thought you had this nailed and posted about the vent temperature in a separate thread. Why you flush it again? You did not do it right first time? Personally, I do not flush any A/C system in all the system I worked on and it always works for me. Not many, under 10 cars. I also never open up any connections to do a 'better' job unless I had to. The reason is that any connection opened introduce a possible failure point in the system. Personally, the fixture you made in my opinion is an overkill. The fact is that you hope you ain't need it again, unless, you are an A/C professional doing it daily.

Good luck this time around.
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  #10  
Old 09-25-2016, 08:31 PM
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I flushed again because a week later, one of the large compressor o-ring's started to develop a slow leak. This compressor pressure tested good before I installed it. I replaced all the o-rings in the hose fittings but took a chance not resealing the compressor. In hindsight, that was not a smart decision. I found some pretty horrible looking o-rings in a few fittings, I should have known better that the o-rings in the compressor are in similar conditions. I did a complete reseal of the compressor this time and a full system flush. I was down 1.5 weeks having to wait for parts to come in. AC is working again with a temporary refrigerent in it (R152a). I'll save the R12 till I run the system with R152a for a while (at least a few months).

There is no way to put in the correct amount of oil after some has leaked out. That is why I did a system flush again. I just read about a device on Red Tek's site that can tell how much oil is in the system. If it really works, it could save a lot of work in some situations.
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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
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  #11  
Old 09-26-2016, 09:23 AM
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..............Personally, I do not flush any A/C system in all the system I worked on and it always works for me. ...............Personally, the fixture you made in my opinion is an overkill. The fact is that you hope you ain't need it again, unless, you are an A/C professional doing it daily.

Good luck this time around.
Of course it's overkill for you, since you confessed to never flush. But if you ever find the need to flush, the adapters makes the job a breeze instead of a curse. It's OK if I use it only once. It was worth it! It is good to know that if I ever need it again, I have them in the toolbox.
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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked
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  #12  
Old 03-29-2017, 12:18 AM
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Bump

GPS
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  #13  
Old 03-30-2017, 09:50 AM
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Originally Posted by compress ignite View Post
GPS
Huh? GPS???
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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked
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  #14  
Old 04-27-2018, 09:51 AM
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Thumbs up HVAC Tips

This thread reads great but all the photos are gone.......
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  #15  
Old 04-27-2018, 11:08 AM
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https://www.google.com/search?q=photobucket+hotlink+fix&rlz=1CATAAB_enUS627US627&oq=photobucket+hotlink+&aqs=chrome.0.0j69i57j69i60l2j0l2.13787j0j7&sourceid=chrome&ie=UTF-8&hotlinkfix=1524841580035

Works great on a Chromebook. Ymmv depending on what browser you use.

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