I am also a believer in LONG vacuum pulls... used to be Overnight was standard ...
ALSO ... if one has Nitrogen available ....

TRIPPLE EVACUATION is a standard procedure for HOUSE AC units.. where Flushing is not practical...

this means filling the system with ( DRY ) nitrogen.... letting it sit ( watch for leaks by monitoring the gauge pressures ) vacuuming it OUT..

and REPEATING THIS PROCEDURE...... three times is standard.....

the idea is that the very dry nitrogen will naturally absorb some moisture each time...and you can take it out by vacuuming ...

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

in re: Funola & 97SL320/valve core removal

In the R-12 days I used a tool that allowed you to remove the valve core w/o losing gas, and then replace it post evac & fill. Haven't bothered to get one for R-134A automotive ports.

Core removal made dye & oil injection easier, and cleaner. Long vac pulls are good if you have the time, but ambient temp is also very important. The purpose of a 29.9mmHg vac is to drop the boiling point of water to just below 70F. The modern technique is to have a micron gauge and to use your 'super duper' pump to pull down to 400 microns or so. I cheat. I use a heat gun while pulling a vac. I heat up all the metal bits to help the evacuation of moisture. If I am certain that moisture got into the system, I have been know to inject 90% isopropyl alcohol (small amount) & then draw it thru the system (reverse flow). The theory is that the alcohol will attach to the water and as a solution will evaporate more quickly while using vac & external heat.

Is this from personal experience having tested it both ways or just theorizing? There are people selling big diameter hoses who run tests with micron gauges hooked up claiming faster evac while achieving lower micron levels with Schrader core removed + big dia. hoses. Are they just trying to sell you stuff?

As for removing the hose and getting air in, that won't happen if you charge with the magic core removal tool (the type with a ball valve) + manifold gauges. Purge the charge hose before connecting to the manifold. When finished charging, install the Schrader core before disconnecting the magic core removal tool.

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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

This is from what I know about CRT manufacture. A 35 / 36 / 38 " tube will achieve very near 29.9 In / hg within 3 / 4 minutes while pulling through a glass tube about 8 mm ID. To get down to CRT vac levels, it takes 4 hours while baking the tube in an oven to get the last few molecules out. This is a level that no one would ever be able to attain in an AC system.

A standard automotive ac system has a fixed volume that really isn't that large. Sure, in the first two minutes a larger hose may offer greater flow, however as the vac reading gets larger, there is less flow through the valve. When you hit anything near 20 in / hg , flow is minimal since there isn't much air in there. Time under vacuum is important to allow moisture to boil off.

On a vehicle with dual AC / bus or large commercial system, larger ports would help but that is beyond the scope of what we are trying to do.

what funola says in the next post is the cheapest way.

Getting a nitrogen regulator for a gas canister is the off the shelf way.

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

"Trying to make the adapter costs the same amount."

Same amount as what? I have a 20 lb Argon tank and Argon shares the regulator as Nitrogen and Co2 afaik. I took an old AC manifold hose, cut the fitting off one end and hose clamped it to the regulator barb. Voila, instant adapter.

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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

I did not think of that brilliantly simple solution. :-/

I retract my previous post---thats the way to do that.

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

Argon and Nitrogen use the same high pressure side regulator fitting: CW male thread , rounded pressure fitting ( CGA 580 ), CO2 uses a female thread , flat face fitting with sealing washer ( CGA 320 ) https://www.concoa.com/cgachart.html

This is all becoming more complicated than it needs to be. Locate a 1/4" female AC fitting with a valve depressor, adapt this to a 1/4" hose barb. ( maybe larger barb depending on what you find the the welding place below. )

Go to a welding supply house, ask them for a fitting that screws into the low pressure side of a MIG welding regulator , they can even supply some 100 PSI min hose and crimp both ends of it.

You now have something to pressurize your AC system regardless if you use Argon or Nitrogen.