Proper? You make the call, but for ten bucks worth of refrigerant you can evacuate, refill and chill.

No replacing anything else: no new seals, no new dryer, no new oil---nothing.

Next year, add another can; mine was done Feb 2012 and just added another can last week.

Did the research - see:

Propane(R-290)&Isobutane(R-600a) 60/40

My posts:
AC compressor will not engage after evacuation - Benzworld.org - Mercedes-Benz Discussion Forum

Charging with propane...how? - Benzworld.org - Mercedes-Benz Discussion Forum

A very sad day indeed - should I keep it or sell it at a low price - Benzworld.org - Mercedes-Benz Discussion Forum

Well its that time of year again! - Benzworld.org - Mercedes-Benz Discussion Forum

Not my posts:
Charging with propane...how? - Page 2 - Benzworld.org - Mercedes-Benz Discussion Forum

R-12 vs Propane vs R-12a (time to recharge A/C) - Benzworld.org - Mercedes-Benz Discussion Forum

Using propane instead of R-12 for A/C - Benzworld.org - Mercedes-Benz Discussion Forum

AC problem solved with propane- Did I plan for suicide - Benzworld.org - Mercedes-Benz Discussion Forum

Other stuff
And apparently you do not have to change the drier with this either

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This gives charges of approx. 40-45 % of R 22, R 12, R 134a or R 404A charge in grams, according to the data from table 1, which also corresponds with empirical values.
hydrocarbons21.com

Per ghg: [60% propane / 40% isobutane works better.. pressures are correct

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To evacuate or not when going from R-134a to R-290 & R-600a? Yes.
Per ghg - paraphrasing of course: there is a possibility of the R134a breaking down to acids when exposed to moisture. Since propane could have moisture then it seems necessary to evacuate. If not evacuated then moisture level should not exceed 10-20ppm; however, if it is evacuated the moisture level can go up to even 1,000 ppm.

1100 grams R-12 - - that is what our w124's call for. And then I calculated the rest:

38.8 oz. R-12
40 - 45 %
15.42 - 17.46 oz.

And @ 60/40 by weight
Propane/Isobutane (oz.)
9.25/6.17 - 10.47/6.98
If 8 oz. of Giga then 1.2 oz. Propane + 6.8 oz. of Iso-Butane
Need additional 9 oz. Propane

• GigaPower Fuel 110 Gold - This is the one I chose and your calculations may differ based on the refrigerant you choose.
Giga 250 grams = 8.818 oz. Then 1.3 oz. (R-290) + 7.5 oz. (R-600a)
Need to use 7 oz of the R-600a and then an additional 9.2 oz (R-290).

Can (GP250G) is acutally 7.76 oz. --- only need 7oz and then 9.2 oz of (R-290).

Thanks,
cool in atl