Heating Output Too Low

SYMPTOM DESCRIPTION:

Air outlet temperature is too low when maximum heating capacity is required.

CAUSE/REMEDY:

^ COOLANT CIRCULATING (AUXILIARY) PUMP INOP.
^ HEATER VALVE NOT FULLY OPEN.
^ ENGINE COOLANT THERMOSTAT DEFECTIVE.
^ HEAT EXCHANGER RESTRICTED OR DAMAGED.
^ BLEND AIR FLAPS NOT FULLY OPEN. If OK, check blend air flaps for free movement.