Suspect blend door actuator
also check heater hoses if both hot if not u may need to have it flushed

Engine cool
lower the coolant level
Locate the two hoses running to the heater core
disconnect them at the engine side leaving hoses connected to heater core throw the firewall
use garden water hose and compressed air if possible
run the water and follow by air throw one side and out the other and vice versa
do that two to three times watching what leaving the heater core you are looking for the good flow and clear water to run throw
check thermostat and replace too
good luck

need manual CHECK IT @
http://www.2carpros.com/kpages/auto_repair_manuals.htm

Answered by BMRFIXIT (expert)
19,736 answers provided