how much r134a has to be charged

[Peter]

I’m repairing/upgrading  my aircon, which is a Frigiking with pre-cooler behind the bumper. The York will be changed for the (successor of the) Sanden 508 and i.s.o  r12, r134a will be used.

Does someone know how much a134 has to be charged to this system with cooler, pre-cooler and Sanden 508?

Thanks for help

[Benz Dr.]

I think it should be 1 kg.

[Shvegel]

I believe there is a sight glass on the top of the drier unit at the firewall?  If so if it were an R-12 system you would charge it until the sight glass showed no bubbles but R-134a requires 85-90 percent of an R-12 charge.  R-134 systems run at higher pressures so the reduced charge helps to limit that.  My general unscientific method is to charge it until the sight glass shows some bubbles.  R-134a requires a sybthetic oil which is not compatible with the mineral oil normally found in R-22 systems.  You should replace the filter drier unit at the firewall to remove and mineral oil that may have accumulated in the drier unit.  These systems are designed to be fairly robust with relatively large filter driers that also act as a suction side accumulators or reservoirs for any excess refrigerant in the system.  Think of it like the AC systems' expansion tank.  With proper oil (Ester oil is preferred over PAG oil) and a new compressor designed to handle the higher pressures I wouldn't worry too much about overcharging it.  Even if you filled it until the bubbbles just disapeared you would probably still be OK.