Let's back up! What is wrong with the a/c to begin with? That will determine your course of action.

As far as a vac pump goes, I read that you can leave a deposit at AutoZone and they will loan you one. Sounds like a great deal for the DIYer.

All kinds of things are used to flush an a/c system. What is most economical is to initially flush components with mineral spirits then follow up with regular a/c flush to remove the mineral spirits residue.

I would not try using a venturi pump with a small compressor. You need to draw a vacuum for an extended period of time. You will have to have a really big compressor to be able to maintain a vac on the venturi long enough to adequately boil off moisture.

Good luck,

I suspect the main problem with my unit is that it was converted to 134a by a previous party. It is cool but not cold. The previous party did not restore the fan switch on the drier(may not be a new drier). Instead a stud bolt is there. I know it needs at least the right fluid(r-12) and a drier. The compressor works and there is still 134 a in the system so I don't think there is a bad leak. If I pull the compressor I guess I could test that. All the other non moving parts should be fine as long as they are clean and no leaks(vacuum check will verify that). I want to restore the system back as close to spec as possible without spending a mint.

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My Daily : 96 E-300 Diesel with 195,000 miles
Retired: 92 300D 2.5 T 345K miles and for sale
Retired: 95 E320 157K miles and currently parked with blown engine

Both retired cars are for sale as is my w124 shop inventory

Restore your fan switch first...and see how much difference that makes....

I don't know if that makes a whole lot of difference at freeway speeds. I want to do the refrigerant change anyway. I will pick one up though and install it until I can get around to the other parts.

__________________
My Daily : 96 E-300 Diesel with 195,000 miles
Retired: 92 300D 2.5 T 345K miles and for sale
Retired: 95 E320 157K miles and currently parked with blown engine

Both retired cars are for sale as is my w124 shop inventory

No, probably not at highway speeds... do clean your condensor and radiator fins and be sure they are straight.. that can make an easy 20 percent difference often...

The PO may have installed the temp switch bolt because he may have hot wired the fan to come on all the time. Or at least when the AC is on. If so then do the following.
Check the system pressures to see is you are low on R134a. If so then fill it.
If not then get the fan on and run it all the time the AC system is on. This may be all you need.

Other posted info.

If you flush the ystem. You can use mineral spirits and then AC flush. Get a compressor and a flush gun or a Under coating gun, this is what I used, and completely flush the system. Get new O rings for the system. If buying new hoses then talk to Phil about the manifold hose. I tried 2 and returned them both. Phil was not happy with the hoses either. He may have found a better source. I reused my opriginal Mercedes hose. If you are going to buy a new manifold hose go OEM ($$$$).
New reciver/dryer. If you get a new compressor. Dont get a rebuilt. And make sure it is Mercedes compatable. Saw an artcle about the clutch assembly being rotated 180 degrees on the Mercedes units compared to the GM (for a GM car) units. The oil hole dumps the oil out if its a GM unit and you loose lubrication in the front seal.
New expansion valve if not R134a compatable.
Flushing the evaporator can be a pain if in the car. It will be, so plan on that PITA job.

GO WITH SYNTHETIC OIL. That way when your not happy with the R134a conversion, you can just evacuate the R134a and then install the R12. the synthetic oil is compatable to both R134a and R12.

ACKITS.com is your friend.

Again I would put some gauges on the system and see if you are low on freon. Get the fan working and see how the system does.

Get a good vacuum pump. If you don't pull a good enough vacuum and water is not completely boiled off then you may have the expansion valve freeze up with water as the system operates. A pain to diagnos and then you have to empty the system, replace the reciever/dyer, add oil, evacuate the system and then add your freon back ( if you had a collector) or buy new freon.

For R 134a they sell the top tap (Oreilly's sells them), but remember you should add the freon to the system thru the gauge hoses. Keep the can upright. Do not allow liquid feon to hit the compressor, vapor only. I run the can thru the hoses and advance the idle to about 2000 rpm. As the can get low put it in a pan of warm water. This will boil off the freon. Tthe water temp should allow your hand to sit in it. 100-110*F should be fine. Place a large fan, a box fan is good, in front of the condensor to cool the engine set up.

Dave

__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

4cfm, 120 psi, 2 tank air compressor at Advance Auto $88
25 foot 1/2 inch air hose $8.99 at Agri Supply.
Various blowguns $3.99-$15.00 for the longer bent one at Tractor Supply Co.

2 cfm Mastercool SINGLE stage vacuum pump rental at Autozone $199, you get this back when you return, Have your own oil!
A/C service DVD at Autozone $8.99

Acetone and mineral spirits are fine to use, the Acetone evaporates so fast it will not hurt anything (espicially good for evaporator). Cover seat, carpet, console with drop cloths, it will be messy fumes, use old towels and a baby
bottle to collect flush.

New Delphi (GM/Harrison) R4 for Benz at www.ackits.com - $206, get your pump oil here also.

Get the Filgor rec/dryer, OE and has sight glass.

Charge low side with can upright for gas/vapor. My indy was seen turning can all around and I think that he sumped my compressor with liquid. also he did not purge gauge lines and may have introduced air. I got all kinds of weird readings, so read/study and DIY.

Forget R134a and go with R12!!!!! Have had two SDs converted, you will not be cool and happy!

__________________
1993 Mercedes Benz 300D 2.5 205K (ex wife's)
1984 Mercedes Benz 300SD 320K (SOLD)
2004 Mercedes Benz C240 75K
1995 GMC Sierra 2WD 5.7L 188K
1983 Mercedes Benz 300SD 239K (SOLD)
1987 BMW 325i 220K (SOLD FOR SALVAGE)

609 Certification

Hey,
I think it would help out a lot if those who have done it could detail the flush procedure they used.
The more specific the better

Danny

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1984 300SD Turbo Diesel 150,000 miles

OBK member #23

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I don't know how to add much more detail than was given by Dave and James.

The only thing that might not be obvious to those who have not done it, is that all connections are disconnected and the flushing agent is then blown into the components with the flushing device. It is nothing more than a cannister that can be filled with flushing agent, the top screwed back on and then pressurized through a Shrader valve. You then use the blow gun that is attached to the cannister to force the flushing agent into the component. The components are the evaporator, condensor, lines and expansion valve. Flush the compressor with a/c oil, don't use solvent in the compressor.

After flushing each component, use compressed air to TOTALLY blow out ALL solvent. Even a little solvent left in the system can wreck it.

After everything is flushed assemble everything using new o-rings with a/c oil or nylog coated on them. After everything else is connected, put in a new r/d as the last thing, so it will get contaminated with a minimal amount of moisture from the air.

Good luck,

Hey,
Yeah it's a pretty simple process. I wasn't planning on using a flush gun though so I was more interested in the size of the fittings.
My plan was to get hose and hose clamps and pour the flush agent into the component and blow it out with compressed air. So I would need hose, clamps and a way to connect a funnel.
Do this in both directions a couple of times.

How is a flush gun better? It doesn't look like there's a mechanical connection. Doesn't that make a bloody mess?
I wouldn't mind buying one even though it will probably only be used once if I thought it would make that much of a difference.

Danny

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1984 300SD Turbo Diesel 150,000 miles

OBK member #23

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On the 123 the manual says to take the innards out of the old expansion valve... and leave the hoses attached which go from it forward through the firewall.... take them loose from the items they attach to in the engine compartment..
Then attach the flush gun to the expansion valve and flush both those lines at the same time.

You may want to be careful when buying AC flush. Usually, "AC flush" is being referred to without any extra qualifiers, making it sound like it doesn't matter exactly what you buy, as long as it says "AC flush" in the bottle. Not all of them are the same though. I made a mistake of buying Interdynamics AC flush (O'Reilly's sells it, and it's the only kind I could find in a local autoparts store). Well, turns out Interdynamics flush is oil-based (you can look it up on ackits.com forums), and it just does not evaporate. Which means that if you try to blow it e.g. through a condenser, getting all of it out will be really, really hard. I suppose it may be fine for flushing hoses, but for a condenser or evaporator flushing it's just not the right stuff. Acetone works much better there, and you know that it will evaporate when you blow enough air through the system. I don't know whether it's OK to use acetone on non-metal hoses though, I could argue it both ways, and I haven't seen an authoritative statement on the issue. So when you are buying AC flush, make sure it's the kind that evaporates without leaving any trace.

I have seen professionals who say not to flush the evaporator or condensor unless you have it out in hand....where it can be turned various directions to get the stuff out (while blowing with air)....

We should check with Tray at Carlisle to see what kind they carry...and provide with the flush gun they sell...

The flush gun works good because there is a rubber seal around the mouth of the gun so that it seals well and forces the solvent through the component.

A common approach is to use brake cleaner straight from the aerosol can.

Good luck,

My A/C suffered a set back when the place I got it from "recharged" it with a little 134a when it had R12 in it (two years ago before I got the car)....needless to say it worked fine for a while then started having problems (not cooling much at all....compressor stalling the engine occassionally.....but I think that could have been rack-damper related...) so I disconnected the cable to the a/c clutch a long time ago. Today out of curiosity I rotated the compressor by hand and it moves freely both clockwise and counter clockwise, no binding or resistance that I could tell at all, it never did actually lock up when I was still using it.......which the one on our 83 just did, I tried to rotate it by hand, it will go backwards smooth and fine, but clockwise it goes almost one turn the goes "clank" and stops frozen solid, like it jams or something. Since mine is not seized and I disabled it, I am wondering if I just.....replaced the hoses and reciever-dryer + the expansion valve etc....and had it completely flushed and recharged....if there'd be a possibility it'd work ok again. If needs anymore than that I don't see it as worth it and I'll just not do it....but if that'd work it'd be awesome.

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