Heating Performance Diagnostics (Auxiliary System)
WARNING: This page is about a different car, the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, and 2002 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
For diagnosis see HEATER PERFORMANCE TEST (AUXILIARY SYSTEM)
under PERFORMANCE TESTS in EXPRESS & SAVANA article in HEATER SYSTEMS.