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Heater-Evaporator Box

Symptom
The vent selector knob turns freely without resistance and with no change in airflow direction. Conversely, the vent selector knob can be excessively stiff.

Cause
Inside the cabin HVAC assembly (aka “heater/evaporator box”), a rotating drum redirects air flow to the desired vents. When new, the drum is lubricated with grease and turns with ease. However, over time the grease hardens and the drum binds up. In a vehicle with manual vent selection, this can be felt through an overly stiff knob. Invariably, the control rod breaks leaving the vent selection stuck in one position.

Cure
Saab recommends a repair that relieves pressure applied to the vent selection drums. If the repair is unsuccessful, replacement of the heater/evaporator box becomes necessary (an extensive procedure as depicted in the picture below). Unfortunately, the drums cannot be accessed or lubricated without complete disassembly of the dash area.

evapbox01 evapbox02

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