SAVE TIME BY EASILY DETERMINING IF THE A/C SYSTEM NEEDS TO BE FLUSHED The condition of the refrigerant in your A/C system is an important factor in the proper operation of all components and overall cooling efficiency. The only way to actually see the condition of the refrigerant in your vehicle�s A/C system is with the use of the Mastercool visual inspection sight glass. This unit can be used with a standard vacuum pump or with the vacuum function on your R/R/R machine. Easy to follow instructions will guide you through the use of either option.