Question about 1999 Chevrolet Silverado 1500

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My heater wont switch from vent to defrost or any other position were and what do i need to check or replace

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6ya6ya
  • 2 Answers

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Posted on Jan 02, 2017

  • 37 Answers

SOURCE: Heat wont blow through heater or defroster vents

The door in the heater box is most likely stuck. It is located under the dash on the passenger side

Posted on Dec 06, 2008

  • 124 Answers

SOURCE: heater control 98 chevy s10 blazer

These trucks have a problem where moisture builds up in the heater box then freezes. When this freezes and you change your heater settings it breaks the shaft for the blend door. If this is what happened you should be able to look under the dash above and to the right of the gas pedal and you will see two vaccuum accuators one of them you should be able to wiggle around the linkage if it is broke. To fix this you need to remove the entire dash to get the heater box out which involves discharging the AC and draining the coolant because the heater core and evaporator come out. Please rate.

Posted on Dec 13, 2008

  • 20 Answers

SOURCE: Heat wont blow through heater or defroster vents

common problem, check under dash by the gas pedal if control arms are muving went selecting from ac to heat cuz this it is the control for the vents to go from ac to heat and to defrost.

Posted on Feb 23, 2009

chuck943
  • 783 Answers

SOURCE: Vent control

You have a vacuum leak.Defrost is the default postion(no vacuum).
See if you can locate the small black vacuum line that goes inside the vehicle on the passenger side near the heater core. The trace it back,should see it going to a canister then to the intake manifold.Make sure it is not disconnected or broken somewhere.

Posted on Mar 02, 2009

  • 16 Answers

SOURCE: No air blowing from the dash vents

sounds like you have a vacuum problem

Posted on May 04, 2009

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1 Answer

Why wont my 2001 ford windstar blow out of vents ? only on defrost?


Air Flow Control
Air flow control is accomplished in the following manner:
  • Primary control is through the function selector knob , mounted on the heater function selector switch, which is part of the heater control .
  • The function selector knob has the following positions: OFF, PANEL, PANEL/FLOOR, FLOOR, FLOOR/DEFROST and DEFROST.
  • The heater function selector switch combines a vacuum selector valve with an internal electrical switch.
  • The vacuum selector valve directs source vacuum to various vacuum control motors (18A318) . Refer to the System Airflow Schematic and Vacuum Control Charts.
  • An internal single-pole electrical switch is also controlled by the selector. The switch controls the electrical supply to the heater blower motor switch (18578) .
  • The position of the function selector knob determines the manner in which the system will operate.
  • Each position of the function selector knob is detented for positive engagement.
  • You probably have a vacuum leak , Pull heater control panel an check for vacuum . A broke vacuum hose or The vacuum selector valve is bad ! Or check for a vacuum hose in the engine compartment being off somewhere !

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2 Answers

1998 chevy blazer heater problems. wont switch from defrost to floor. stuck on vents right now. how do I fix this problem.


Most likely either the vent switching mechanism is dirty and won't switch the flaps -or- most likely the vacuum that is used to turn the vent flaps is either leaking and not pulling enough vacuum. You will have to get underneath the dash near the center, to check and see if you can manually move the vent flaps. If so, then most likely it is a vacuum leak in a vacuum line to the flap mechanism.

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1 Answer

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Check all vacuum lines that goto the heater control under the right side of the dash.....also check for any connector that are disconnected. Good Luck

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1 Answer

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It sounds like the mode actuator is defective. It is what changes the different modes, floof,vent,defroster.

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1 Answer

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Check the vacuum hose going to the heater control valve,it may have popped off. If that is on. check the vacuum hose going to your recirculation door under the right side of your dash. I hope this helps.

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1 Answer

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check for a vacuum line that has fallen off the diaphram vacuum "switch can" near the vent shift lever at the heater box under the dash passenger side

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1 Answer

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