The PO had the a/c converted to 134a on my '91 350SD. The system is barely cooling now that summer-like temperatures have arrived here in NJ. With a proper charge, what gauge pressures should I observe with outside temperature in the 80-85 degree range?

Greg

Someone will know the specific answer to your question..
but to get the proper readings as you add refrigerant you need to be sure that a proper amount of air is being forced into the condensor area...aux fan and engine fan are not enough .... Not having enough is one of those times which the FSM lists as potentially giving a false reading on the site gauge ( which really should not be used ).... the gauge readings are the proper way to do it... go slowly and let the system stabilize as you slowly add refrigerant/check gauges...

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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

the answer is dependent on several factors.
as mentioned above, airflow across condenser is critical.
your vehicle has the awesome parallel flow condenser, so if you are not getting cooling, it's DIRTY! you need a really good coil cleaner to get in those small areas. it's gotta be CLEAN to work.
also your fan clutch needs to be working, and your aux fan/fans need to be working top notch. ALSO a LARGE fan needs to be directed at the front of the car when checking the charge.
IF all that is done,
80-85 ambient with 50% RH and your windows all down, and the system set to max cool max fan
the high side should read around 190 low should be in the range of 36-41 depending on temp/TXV flow.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Thanks guys. Exactly what I was looking for. I'll report back.