Hope this helps
BASIC HEATER SYSTEM TROUBLE SHOOTING CHART
CONDITIONPOSSIBLE CAUSE
Insufficient, Erratic, or No Heat
. Low Coolant Level
. Incorrect thermostat.
. Restricted coolant flow through core.
. Heater hoses plugged.
. Misadjusted control cable.
. Sticking heater control valve.
. Vacuum hose leaking.
. Vacuum hose blocked.
. Vacuum motors inoperative.
. Blocked air inlet.
. Inoperative heater blower motor.
. Oil residue on heater core fins.
. Dirt on heater core fins
Tuesday, July 14th, 2020 AT 11:18 AM
(Merged)