This is for a 98, probably the same for the 99.
What it doesn’t show is the hard line from the PCV fitting to a solenoid on the firewall by the a/c accumulator. This solenoid has a second hose that goes to the water valve on the heater hoses. When the a/c panel temperature dial is set to the “max†detent, the solenoid is energized, applying vacuum to the water valve and closing it. This shuts off coolant flow to the heater core, supposedly maximizing a/c performance.
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