Question about 1998 GMC Safari

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I cant switch the heat from the various vents

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  • zookcg Mar 07, 2009

    Can't switch the heat or a/c to any vents other than defrost

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99% sure that this is your problem. It's not a linkage issue, but a vaccum control problem. There is a thin (1/8") plastic vaccum line that traverses over the top of your engine. The high heat generated by cramming a 4.3 ltr. engine into the tight quarters of a Sarfari or Astro van causes the plastic tubing to breakdown, crumble and leak. The vaccum line needs to be replaced from the vaccum manifold at the rear of the engine to the heater control access on the firewall (about 3-1/2 ft. of tubing). Unfortunately, you'll have to remover the interior "doghouse" to access the vaccum manifold at the rear of the engine. The line is worth a couple of bucks, should take a mechanic less than an hour to complete the repair. You can then redirect heat or A/C from the defrosters, to dash vents, to your feet...etc.
Good Luck
Wray Breen

Posted on Jan 25, 2009

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Popped open the hood...
Found a vacuum hose with a small plastic tubing broken off at the end of the vacuum hose.
Pulled out the broken plastic tubing and attached vacuum hose to the original plastic tubing that connected to broken piece.
Instantly fixed vent problem without doing anything other than opening hood. Thank poster mwbreen for giving me information to try the fix myself.

Posted on May 11, 2009

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That is a linkage issue.  If you are mechanically incline check into what type of system is used for that linkage.  some vehicles use mechanical, some use cables, and some use vacuum lines.  if not just take to a shop.  best of luck!

Posted on Jan 22, 2009

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