Im replacing compressor , expansion valve , and receiver-dryer to upgrade old system and convert to r134a.Is there a logical routine to keep the new reeiver/dryer from absorbing the old moisture while waiting for busy a/c shop to have time to evacuate and recharge ?
Thanks for any thoughts;
Georgey
82 300td

The A/C system must be evacuated before you replace the refridgerant. Replace your parts. Once the system is buttoned down, have it evacuated with a professional . You may want to have it filled with refridgerant at the same time. It will proably cost you the same or less than doing it yourself. They also have professional A/C gauges to diagnose a problem when the system is brought back to life, especially when things don't go right.

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1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T

my concern was wont the new receiver/dryer be contaminated by the old refrigerant if I have to wait a couple of days before the ac shop can evacuate and recharge system. Is the timing critical or am I being to fussy ?

Brother of thr Benz, ghj
You're on the right track, wanting to protect the new components.
The discant in the drier will absorb moisture from the atmosphere, but won't be contaminated from the system provided you don't engaged the clutch and put the compressor in operation.
If you must have ventilation, operate in the "economy" mode.
Your technican will finish servicing the unit by evacuating, holding at minus pressure to thoroughly dry the unit, check for pressure rise and finally charging.
Enjoy your efforts.
Happy Trails Beep Beep from The Spiderman in Houston!!!

Thank you all . Just discovered this fine forum and think it clearly outshines the others for clear help on my finicky but loved mercedes.
Thanks again
Georgey

Brother of The Benz, georgey
Welcome, welcome, welcome
Happy Trails Beep Beep from The Spiderman in Houston!!!