I bought a cheap one from Harbor Freight here in Florida as a last minute deal. It was the venturi type. Pulled between 28 & 29" & got about 35 degress F out of the center vent. Don't pay more than 10-$15 for one. Just a cheap venturi setup. Murder on your compressor though-runs constantly.

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1984 300CD red/blk 290,000 partial resto
1980 240D 4 sp Brn/palomino gone
1997 Mazda Miata STO edition wife's baby
1988 Lincoln Mark VII LSC next resto
1986 Subaru GL wagon daily
1993 Isuzu pickup field beater
2008 Honda Civic EX-L 5sp wife's new car
1978 Honda XL350
1974 Honda XL70 my Calif. ride in HS