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if the blower motor resistor goes out usually you are stuck with one or 2 speeds.  It may need to be replaced.


the selector switch for the vents is vacuum operated, there may be a vacuum leak somewhere, the selector may have gone bad, or the vacuum motors may have stopped working.


In my Comanche when i have low vacuum it defaults to the defrost vents.

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From Trouble Shooting in 88 Service manual

Air Flow Changes During Acceleration

  • Vacuum system leak.
  • Bad check valve or reservoir.
Air From Defroster At All Times
  • Vacuum system leak.
  • Improperly adjusted control cables.
  • Inoperative vacuum motor.
Blower Does Not Operate Correctly
  • Blown fuse.
  • Blower motor windings open.
  • Resistors burned out.
  • Motor ground connection loose.
  • Wiring harness connections loose.
  • Blower motor switch inoperative.
  • Blower relay inoperative.
  • Fan binding or foreign object in housing.
  • Fan blades broken or bent.
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alright so there r two hoses going to the reservoir in the front bumper. one is the big hose which comes from the intake to supply the vacuum, the other is small and run into the pass. side firewall next to the purple line that runs the coolant regulator for the heater core, i assume that the one that controls where the air blows in my truck, cause its broken.


this is not mine this is a ref. pic from the web. but this is the line that is broke its just further down the line next to my battery, the brighter colored line is the one that goes to the coolant regulator valve for the heater core. so is the broken line the one that controls where my heat blows?

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Any vacuum leak between the reservoir "ball" and the dash will cause it to only blow on defrost. You just need a small piece of hose to repair the crack and you can also try a piece of tape for a temporary fix. The blower resistor is mounted on the passenger side under the dash. There is usually a plastic cover over it. I would start here if you only have high speed for the fan.

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vac line is like a low pressure air line......you do not need the original line to test it......electrical or duct tape will give you enough of an answer to send you down the right path.....patch it up and see if it gets better...if so .....now fix it

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