How much Refrigerant to use - PeachParts Mercedes-Benz Forum

bluebird · #1 10-06-2011, 02:01 PM

Can someone tell me how much refrigerant is needed in a 1984 300SD by weight? I have searched but could not find the info. Thank you.

leathermang · #2 10-06-2011, 02:06 PM

Are you going to be installing it yourself ?
If yes, what tools, gauges, etc do you have ?
Will this be a clean install .... meaning you have flushed your lines, condensor, and evaporator ?
This will become important with regards to the correct amount of oil for your system.
Are you working from a big tank or small cans ?
Do you have the proper type of weighing equipment ?

engatwork · #3 10-06-2011, 02:09 PM

If I remember correctly I believe it is 2.2# of r12.

leathermang · #4 10-06-2011, 02:12 PM

Jim, how do you know which refrigerant he is going to use ?
He needs to share more info with us...

engatwork · #5 10-06-2011, 02:27 PM

I don't know what refrigerant he is going to use. I posted what I remember MB specifying in 1984 using r12.

bluebird · #6 10-06-2011, 08:43 PM

I am not going to be doing the installation, a friend of mine who is certified and works for Penske as a diesel mechanic is going to do the work.

He has all the equiptment and then some to do the job, tool wise he is well equipt other than that you will have to ask him.

I hope it will be a clean install. I know nothing about the current system other than there is no refrigerant in the system now and the current R4 is seized. I have purchased a new R4 compressor, new dryer and expansion valve. I will purchase the flush and oil for R134, the evaporator will not be replaced unless necessary after pressure testing.

He will be working with a large tank of R134 and the proper scale (weighing equipmnet).

Is there a difference in the amount of refrigerant needed between R12 or R134?

engatwork · #7 10-06-2011, 08:52 PM

Quote:

Is there a difference in the amount of refrigerant needed between R12 or R134?

yes

Keep in mind that unless you update the condenser to a parallel flow unit it will never perform as well as it did using r12.

leathermang · #8 10-06-2011, 08:56 PM

Yes, the amount of R134a installed in a system is typically 80 percent of what the R12 amount would be.

The worst thing you can do with regards to amount of refrigerant is put ANY too much... it will work your system to death... the way an AC works is based on phase change....and if you have too much refrigerant or oil that works against the cause big time.

You should read the sticky on AC in my signature.

There is a way to make sure you do not have too much in the system.... for instance, if a different than stock component were installed like the condensor.... that is to get close to the amount you know you need and then add a couple of oz and make sure the system is stabilized while taking the vent temperatures and the pressure readings from the high and low side...
This method for safe determining of the amount is described in the archives..
The system will cool just fine with several oz less than the amount listed as ' full '..... so if you get to the proper vent temperatures and pressures but have added a little less than what you expected... hold there and see if that works well....