Could be the heater bypass valve is stuck or the heater core
I'd check the heater core
first.You may have trapped air in the cooling system or the heater core may
be partially plugged up. Engine coolant is delivered to the heater core
through two heater hoses. With the engine idling at normal operating
temperature, set the temperature control knob in the full hot position,
the mode control switch knob in the floor heat position, and the blower
motor switch knob in the highest speed position. Using a test
thermometer, check the temperature of the air being discharged at the
HVAC housing floor outlets.
Ambient Air Temperature 15.5° C (60° F) 21.1° C (70° F) 26.6° C (80° F) 32.2° C (90° F)
Minimum Air Temperature at Floor Outlet 52.2° C (126° F) 56.1° C (133° F) 59.4° C (139° F) 62.2° C (144° F)
If the floor outlet air temperature is too low, Both of the heater
hoses should be hot to the touch. The coolant return heater hose should
be slightly cooler than the coolant supply heater hose. If the return
hose is much cooler than the supply hose, locate and repair the engine
coolant flow obstruction in the cooling system.
OBSTRUCTED COOLANT FLOW
Possible locations or causes of obstructed coolant flow: Pinched or
kinked heater hoses. Improper heater hose routing. Plugged heater hoses
or supply and return ports at the cooling system connections. A plugged
heater core. If proper coolant flow through the cooling system is
verified, and heater outlet air temperature is still low, a mechanical
problem may exist.
Possible locations or causes of insufficient heat: An obstructed
cowl air intake. Obstructed heater system outlets. A blend door not
If the heater outlet air temperature cannot be adjusted with the
temperature control knob on the A/C Heater control panel, the following
could require service: The A/C Heater control. The blend door actuator.
The blend door. Improper engine coolant temperature