• Tiny
  • foggyriverboy
  • 1999 Dodge Truck
  • 6 CYL
  • 2WD
  • automatic
  • 90,000 miles

Why does the heater in my 1999 dodge 1500 go from floor to dash when I accelerate? It sounds like the fresh air door opens and then shuts when I let off the gas? I also noticed that my transmission doesn't shift up as fast since this started? I don't know where to start looking for a vacuum leak?

Do you
have the same problem?
Monday, December 13th, 2010 AT 2:17 AM

1 Reply

  • Tiny
  • caradiodoc
  • Expert
  • 25,783 posts

After you check for vacuum leaks, locate the vacuum check valve along the firewall under the hood. It's black, and about the size of a stack of three nickels. Replace it with one that has a storage canister built in. If you check enough vehicles in the salvage yards, you'll find a few in various vehicle models. This one is about 2" long and 1 1/4" in diameter.

The system is spring-loaded to go to the defrost position if there's a vacuum failure. Your feet might freeze but the windshield will be clear. It's a safety thing. Vacuum goes low during accelerating. That's why the system switches.


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Monday, December 13th, 2010 AT 2:23 AM

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