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When you can't get any heat from your vents.

The most common reason for your vehicle to not have heat is caused by being low on coolant in the radiator, this is assuming the blower motor is blowing air out the dash and that is is just not hot.

Heating System

You may have heard the advice that if you car is overheating, open all the windows and run the heater with the fan going at full blast. This is because the heating system is actually a secondary cooling system that mirrors the main cooling system on your car.
heater hoses

A heater core looks like a small radiator.

The heater core draws its hot coolant from the cylinder head and returns it to the pump -- so the heater works regardless of whether the thermostat is open or closed.

Heater Core

Poor Heater System Performance

CAUTION
Check all fluid levels and adjust as needed, before operating vehicle for extended periods at idle.

  1. Start the engine.
  2. Idle the engine until the thermostat opens (upper radiator hose will be hot) Is the engine at normal operating temperature (approx. 200� F)? If yes, go to the next step. If no, go to step 16.
  3. Set the mode selector to FLOOR mode.
  4. Set the heater control selector to the warmest temperature setting.
  5. Set the blower speed the lowest setting.
  6. Carefully feel the inlet and outlet heater hoses at the heater core. Is the inlet heater hose significantly hotter than the outlet heater hose? If yes, go to step 14. If no, go to the next step.
  7. Set the mode selector to PANEL mode.
  8. Select the maximum blower speed.
  9. Select the warmest temperature setting.
  10. Place a thermometer into the center I/P PANEL air outlet and affix a second thermometer to the heater core outlet heater hose.
  11. Record the temperature at the center I/P PANEL air outlet and at the heater core outlet heater hose. Are the two temperature readings about equal? If yes, go to the next step. If no, go to step 13.
  12. Inspect and repair the cowl, cowl area, recirculation door, and the HVAC evaporator/heater core case for cold air leaks. Repair any problems found, go to step 17.
  13. Inspect the temperature door operation. Repair any problems found, go to step 17.
  14. Turn OFF the engine. Back-flush the heater core. Start the engine. Select the FLOOR mode and the lowest blower speed. Select the warmest temperature setting. Feel the temperature of the inlet and outlet heater hoses at the heater core. Is the inlet heater hose feel significantly hotter than the outlet heater hose? If yes, go to the next step. If no, go to step 17.
  15. Replace the heater core. When the repair is completed, go to step 17.
  16. Check for low engine temperature problems, Repair or replace as needed, go to step 17.
  17. Operate the system in order to verify the repair. If the system operates properly, the repair is complete. If the heater still does not work properly, repeat the entire procedure.
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