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Old 03-21-2012, 05:39 PM
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JamesDean JamesDean is offline
Electrical Engineer
Join Date: Apr 2005
Location: NE Ohio
Posts: 5,016
420SEL AC Pressures

Hey everyone,

With this recent warm up, I've decided to go through the cars and check AC systems. Much to my surprise my 190E's works, in the past it had leaked out and stopped working. However my 420SEL's is not working so well.

The compressor kicks on, I put the manifold on it and got 60 PSI static pressure, with engine on readings with the aux fan on and ambient temp at front of radiator about 80F:

According to charts at 80F ambient one should see ~18 Low, 170-210 High.

I saw,

At Idle:
3 Psi Low, 100 Psi High

At 1500 RPM:
0 Psi Low, 100 Psi High

So I felt that the charge was low, so I grabbed a can of R12 and started charging.

20 low, 165 High

10 low, 165 High

I checked the gauge I put in the center vents, it was hitting high 60s. So I thought it was still undercharged a bit. I think I overcharged a bit, I ended up with:

30 low, 175 High

17 Low, 180 High

That's a question I have about these charts are these pressures at idle or at a higher rpm?

What do you guys think?

EDIT: After a short trip (~40mph speed) I achieved about 55F at the center vents with my cheapo dial thermometer.
EDIT: Did another run on the freeway, used my DMM with temp sensor, lowest was 56F. Sat between 56-58F.
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82 300SD 145k
82 300SD 265k
87 420SEL 230k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
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93 300E 195k

Last edited by JamesDean; 03-21-2012 at 06:24 PM.
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