Using a special tool, install to the heater core one side and the other side is clogged.
Place the heater core in water, then apply 200kPa (29psi) pressure.
Holding for two minutes, while checking for leakage from the heater core. If there is leakage, repair or replace the heater core.
VACUUM MOTOR
Connect vacuum tester to the each vacuum connectors and apply-510mmHg pressure.
Check vacuum hiss from the diaphragm of the vacuum motor and that the shaft returns smoothly to initial position. If not okay, replace the vacuum motor.
NOTE
Never manually operate any vacuum motor or vacuum motor controlled door. This may cause internal damage to the motor diaphragm.