Author Topic: How to: Adjusting the 1977-1987 (91) A/C Mode Door - Blend Door Link  (Read 16643 times)

Offline bd

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Mode Door/Blend Door (Bi-Level Baffle) Timing Adjustment:

Referring to the diagram, the bi-level baffle slave link (#153) is an adjustable rod that connects and times the motion of the bi-level baffle (aka, blend door - #163) to the position of the vacuum actuated mode door (#171).  That is, the position of the mode door (the master) directly determines the position of the bi-level baffle (the slave) in a specific way that must be properly timed.  Adjustment of the baffle link significantly impacts air distribution through the respective dash, defrost and floor outlets.

Adjusting the Mode Door/Bi-Level Baffle relationship entails a relatively simple procedure...
  • Remove the glove box door assembly.

  • Remove the two screws that retain the dash outlet duct plenum to the face of the heater case and the single screw that retains the plenum to the dash duct, then remove the plenum.

  • Separate the bi-level baffle slave link (#153) from the nylon split connector (#154) that protrudes from the top of the bi-level baffle shaft (#160) by lifting upward on the link.


  • Physically rotate the mode door shaft (#157) all the way CCW by pushing the mode door (#171) inward against spring tension to its stop and hold it in that position.

  • Rotate the bi-level baffle shaft (#160) all the way CW to its stop and snap the threaded slave link (#153) downward to engage the nylon split connector (#154) locking the baffle to the door.

  • Reinstall the plenum and glove box door assembly.

The adjustable neutral position bracket (#156) and neutral position spring (#159) simply index the mode door and bi-level baffle to their respective neutral or park positions.

For adjustment of the temperature control cable on A/C equipped C/K trucks, see the supplemental technical article: How to: Adjusting the A/C-Heater Temperature Control Cable (All Years).

« Last Edit: May 12, 2020, 08:58:16 PM by bd »
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87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)