Recharging AC Unit - PeachParts Mercedes-Benz Forum

nyko46 · #1 06-09-2008, 02:10 PM

I recharged my AC unit this past Saturday but it still not cold as expected.
I did not apply vacuum to completely empty the old 134a on my 1982 300 SD.
Should I use vacuum to remove all remaining 134a and possible air into the system due the possible leaks or it isn't necessary vacuum the unit?
As it is today the pressure gauge show charge as good but the cold coming from the vents is poor. If need to vacuum the system I am planing to borrow a vacuum machine from auto parts store near by my house. It seems strange but the auto parts store doesn't know if vacuum is needed.
Thanks for your help.
Nyko46

rrgrassi · #2 06-09-2008, 02:15 PM

Did the system have 134 in it before? Have you checked and replaced worn out parts?

What guage are you using? If it's the built in on the can, those are a joke and more often than not totally inaccurate.

Graplr · #3 06-09-2008, 02:30 PM

Have you verified that your compressor works?

Sir Sam · #4 06-09-2008, 02:37 PM

It depends, if the charge was near zero before then you will need to pull a vacumn.

The other thing is, did you charge with the can upside down or not?

nyko46 · #5 06-09-2008, 02:58 PM

Quote:

Originally Posted by rrgrassi

Did the system have 134 in it before? Have you checked and replaced worn out parts?

What guage are you using? If it's the built in on the can, those are a joke and more often than not totally inaccurate.

It had R134a before but I did not replace any other part from system.
I am using 134a cans to refill and I agree that the gauges look like a joke.
What kind of gauge you suggest me to use?
Thanks
Nyko46

nyko46 · #6 06-09-2008, 03:03 PM

Quote:

Originally Posted by Sir Sam

It depends, if the charge was near zero before then you will need to pull a vacumn.

The other thing is, did you charge with the can upside down or not?

Yes, the charge was very low causing the pressure switch to not operate.
I add 134a from cans and put it upside dow to flow as liquid.
I just add three cans and still not cold like any other car.
Any suggestion?
Thanks.
Nyko46

Graplr · #7 06-09-2008, 03:32 PM

Again, have you verified that your compressor is working?
Let's rule that out first.

nyko46 · #8 06-09-2008, 11:50 PM

Quote:

Originally Posted by Graplr

Again, have you verified that your compressor is working?
Let's rule that out first.

Yes, the compressor is working and I can feel the load on engine when the clutch engages. This load sound as an operating compresssor, correct?
By the way, how many PSI is the apropriated charge for a good unit with the system running in maximum cold?

Sir Sam · #9 06-10-2008, 12:37 AM

Quote:

Originally Posted by nyko46

Yes, the charge was very low causing the pressure switch to not operate.
I add 134a from cans and put it upside dow to flow as liquid.
I just add three cans and still not cold like any other car.
Any suggestion?
Thanks.
Nyko46

I have the gauge set from harbor freight:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92649

And the venturi vacuum pump:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92475

But I do alot of AC work for all my different vehicles, so I've paid back my investment.

Generally AC charge isn't done at pressures, but with lbs of refrigerant.

Generally though I like to see 30-40psi on the low side with the compressor running.