Bosch ACS 653 Repair Instruction page 111

Plumbing and Mechanical
ACS 653, ACS 663 Service Manual
PRE-CHARGE PROCESS (for R1234yf only if enabled)
During the pre-charge process (before to perform the charge), the unit charges a small amount of refrigerant in the
A/C system and performs a pressure test to check any leaks.
Figure 4-19. Pre-Charge
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Robert Bosch GmbH SP00D00624 2021-04-08