I am recharging a S500 benz 94 after a hose repair
did a deep vacum 1 hr to 29 put in 3 12 onz cans
what low and high pressure should i look for? i am
in florida and is about 90 outside very humid? so
far i have 40 low 205 high vent temp 50 or so question is the sytem over or under charge? at fast idle it goes to 30 low 215 high

Watching A/C pressures is a very dynamic situation. Its very hard to comment without seeing the whole condition.

Your high side pressures are low which could indicate that you are still undercharged. But, your low side pressures are slightly high which contradicts. Were your aux fans running? Hold the rpm to 2000 for 30 secs. If your low side drops down to 20psi add 4ozs and try again. Unfortunately if you are doing this the car will heat up and cause undo influence on the pressures. This is why the refrigerant should be precisely measured to determine the state of charge.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

thank you for the response the fans were running
they come on and off i will rev the motor like you
suggested

I did like you suggested but after installing the
hoses i found that low side reading was 150 and the high about the same after holding the motor at
2000 rpm for 30 sec the low came down to about 20 high was at 225 fans came on and the high dropped to about 200 i added more freon until it will hold
30 at 2000 rpm high was holding at 210 after going
back to idle it holds at 40 235 then drops to 215 with fans. vent temp are down to like 45 or so. should high and low be the same with the sytem off?

Yes.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

you reply was yes understanding is now correct?

It should put you in the ballpark. If undercharged, it will show bubbles with compressor engaged. If overcharged, you'll will not see any bubbles.

Of course, the 'bubbles' are affected by the temp and humidity. If very hot (90F) and high humidity (85%), it is possible to see bubbles in the site glass and be properly charged.

This is not very accurate and as Steve says, the charge needs to be measured to be sure. But this will give you an idea as to where you are.

You can also check my web page, Menu #14, and note the operating temps and pressures given in the table.

For example, going along at 60mph, you should typically see the EVAPORATOR TEMP SENSOR (test step #5) cycle between 37F to 43F. If so, it's doing all it can do. Of course, very high temp and/or humidity will make those numbers vary a bit.

Hope this helps!

__________________
Regards . . . . JimF
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'94 S500 Cpe

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