I may be wrong, but I thought they all have rear heat comming out from floor vents under the driver and passenger seats. The rear cener vent is for fresh air and you can chose to close it or adjust how much fresh air comming in.

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1991 420SEL Project Car (Completed and rides beautifully) http://www.peachparts.com/shopforum/showthread.php?t=112321
2000 BMW 740IL
2000 Integra Type R - Track Car - SOLD
2005 S2000 - Track Car
06 C230 Sport
89 560SL