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**hatzie** · 08-06-2016, 05:20 PM

You can do it automatically when the AC is on or with a switch or even both.

Four Seasons 74858 5/8" inline vacuum heater valve.https://www.amazon.com/Four-Seasons-.../dp/B000C2Q8OS
2 port 12v Normally Closed Vacuum Solenoid https://www.amazon.com/Universal-Con.../dp/B003R43J2C

The Vacuum valve in the heater hose is the part that will look most out of place. The Vacuum Solenoid looks similar to GM emissions parts.
Tee into AC Clutch + wire or use a switch inside the cab or both.
Tee into AC Vacuum between the accumulator can and the dash control head. The rest of the vacuum routing is self explanatory.

08-06-2016, 05:20 PM	#4
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 5,022	Re: Heater control valve You can do it automatically when the AC is on or with a switch or even both. Four Seasons 74858 5/8" inline vacuum heater valve.https://www.amazon.com/Four-Seasons-.../dp/B000C2Q8OS 2 port 12v Normally Closed Vacuum Solenoid https://www.amazon.com/Universal-Con.../dp/B003R43J2C The Vacuum valve in the heater hose is the part that will look most out of place. The Vacuum Solenoid looks similar to GM emissions parts. Tee into AC Clutch + wire or use a switch inside the cab or both. Tee into AC Vacuum between the accumulator can and the dash control head. The rest of the vacuum routing is self explanatory. __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.