Grand Cherokee 4WD L6-242 40L VIN S MFI (1993) - Vacuum Harness HVAC
**Locate the vacuum source line to the Heater A/C system in the engine compartment (Figure 1 Figure 2, and Figure 3).** Install the vacuum check
valve in the Heater A/C system vacuum line. Make sure that the check valve is installed to allow vacuum to pass into the Heater NO system, but block
any vacuum drop when **accelerating.**