Bosch ACS 653 Repair Instruction page 110

Plumbing and Mechanical
ACS 653, ACS 663 Service Manual
UV DYE INJECT PROCESS
During the Charge process, the unit activates the dye inject solenoid to inject a preset amount of dye into the vehicle
A/C system to check for leaks. The system being serviced must have a vacuum to pull dye from the dye inject bottle.
Figure 4-18. UV Dye Inject
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SP00D00624 2021-04-08 Robert Bosch GmbH