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Mercedes 280E R134a conversion - how much R134a?

Turbine1 on Sun May 03, 2009 1:38 PM User is offline

Year: 1981
Make: Mercedes-Benz
Model: 280E
Engine Size: 2.8l
Refrigerant Type: R134a
Ambient Temp: 80
Pressure Low: 35
Pressure High: 140
Country of Origin: United States

Spent the day yesterday finishing conversion to R134a on this car. AC system was DOA when I bought car 2 years ago and R12 had all leaked out (completely empty) probably years before. Decided to convert to R134a and fix it myself rather than pay big bucks taking it to a shop to fix leaks and replace parts.
New receiver/dryer, new expansion valve, new hi/lo pressure switch, all new seals. Drained and replaced oil in York compressor crankcase (POE oil). Flushed hoses and parts on the car (not the compressor) before installing the new parts. Put it all back together yesterday. Holding a 30 inch Hg vacuum for half an hour or more (went through a couple of vacuum cycles getting residual moisture out first).
Charged with 24 oz R134a (60% of the original R12 charge which is 1.2 kg/40 oz according to the original service sticker in engine compartment).
Getting 38 degree F air from the vents. Hi/low system pressures ~35 and ~140 respectively. Ambient air was around 80 degs F.
Should I add any more R134a to the system? 60% of the R12 charge seems a little low, but the air is coming out pretty cool.
Any advice appreciated,
Thanks,

Kev

Edited: Sun May 03, 2009 at 9:01 PM by Turbine1

TRB on Sun May 03, 2009 7:13 PM User is offlineView users profile

Might be able to add a little, but I would wait until your ambient is a little higher and recheck the pressures. It is always best to try and match the amount listed! Getting as close as you can without creating a high pressure issue is the goal.

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Turbine1 on Sun May 03, 2009 9:07 PM User is offline

Good idea. I will wait till it warms up some more and check it out.
But how high is too high? Should I just aim to keep below the top end of the pressure range in the pressure/temp chart for R134a in the tech tips forum?

TRB on Sun May 03, 2009 10:29 PM User is offlineView users profile

Well it depends on how it is cooling. In Phoenix we see 325 psi with R12 and R134a systems all the time. But anything over that and I start to get concerned not only for cooling but durability.

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

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