3-second answer: Clicking behind the dash when you move the temp knob = the blend door actuator fighting a stuck door or a worn gear. Heat only on one side / no temp change = the blend door or its actuator. On 92-96 trucks the blend door is cable-actuated on some trims and vacuum/electric on others — know yours before ordering parts.
Diagnosis
- Clicking noise — the actuator gear stripped or the door binding. Cycle the temp knob and listen.
- No temp change — check the cable first (a broken clip at the actuator = free fix). Then the actuator motor, then the door.
- HVAC blows through defrost only — that's the vacuum system (see vacuum diagrams), not the blend door.
- Cold coolant smell + wet floor — that's the heater core, different problem.
The fix
- Cable/actuator issues: cheap, dash-side work only.
- Blend door failure: the door itself lives in the HVAC box — replacing it is dash-out on some years, or reachable through the glovebox on others. The common workaround: cut a small access panel in the plenum (like the heater-core shortcut) and replace the door, or install a manual cable override.
- The aftermarket "blend door repair kit" (reinforced door) fixes the famous broken-door problem permanently.
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Threads
- FTE search: blend door