TEST B: INSUFFICIENT, ERRATIC OR NO HEAT
Check For Proper Coolant Level
Check coolant level. If coolant level is low, go to next step. If coolant level is okay, go to step 3).
Check Cooling System For Leaks
Fill reservoir to COLD FILL level. Pressure check cooling system. If radiator and radiator cap hold pressure, go to next step. If radiator and radiator cap do not hold pressure, pressure check heater core. See HEATER CORE under TESTING.
Check For Hot Water To Heater Control Valve Inlet Hose
Allow engine to reach normal operating temperature. Feel heater control valve inlet hose. If hose is too hot to handle, go to next step. If hose is not hot, test cooling system, including water pump, coolant by-pass and thermostat.
Check Heater Core Inlet Hose For Hot Water
Feel inlet hose to heater core. If heater core inlet hose is hot, go to next step. If heater core inlet hose is not hot, go to step 6).
Check Heater Core Outlet Hose
Feel heater core outlet hose. If heater core outlet hose is hot, go to TEST F. If heater core outlet hose is cold, test heater core for plugged condition.
Check Vacuum Supply To Heater Control Valve
Disconnect vacuum supply hose to heater control valve. Select any mode of function selector switch, except OFF or MAX A/C. Check for vacuum at heater control valve vacuum supply hose. If vacuum is present, replace heater control valve. Retest system. If vacuum is not present, go to next step.
Leak Test Vacuum Supply Hose
Disconnect vacuum harness connector at function selector switch. Plug vacuum supply hose at heater control valve. Using a vacuum tester on function selector switch vacuum harness connector, apply vacuum to hose that leads to heater control valve. If vacuum is obtained and does not drop, go to next step. If vacuum is not obtained, repair or replace vacuum supply hose from function selector switch to heater control valve.
Check For Plugged Vacuum Supply Hose
Remove plug from vacuum supply hose and apply vacuum to hose from function selector switch vacuum harness connector. If any vacuum is obtained, replace vacuum supply hose. If no vacuum can be obtained, go to TEST A.