GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1998 🢒 Prizm 🢒 HVAC 🢒 Heating, Ventilation and Air Conditioning 🢒 Heat Excessive

Heat Excessive Heat Mode

Step

Action

Yes

No

1

With the ignition switch in the ON position , turn the blower speed switch from OFF to each of the following positions:

  1. LOW
  2. MEDIUM 1
  3. MEDIUM 2
  4. HIGH
  5. OFF

Does the blower motor speed increase at each speed level when blower speed selector switch is turned towards HIGH and then decrease when the switch is turned towards LOW?

Go to Step 2

Go to HVAC System Check

2
  1. Set the mode control to the to HEAT position.
  2. Set the blower speed to HIGH.
  3. Set the temperature control to the hottest position.
  4. Turn the ignition switch to the ON position.
  5. Inspect for airflow out of the heater outlet.

Is there high airflow from the heater outlet?

Go to Step 3

Go to Step 4

3
  1. Inspect the temperature control cable and linkage operation.
  2. Repair or replace as necessary. Refer to Temperature Control Cable Replacement .

Is the repair complete?

Go to Step 5

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4
  1. Inspect the mode control cable and linkage operation.
  2. Repair or replace as necessary. Refer to Mode Control Cable Replacement .

Is the repair complete?

Go to Step 5

--

5

Perform the function test. Refer to Function Test .

Is the repair complete?

System OK

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Heat Excessive Vent Mode

Step

Action

Yes

No

1
  1. Turn the ignition switch to the LOCK position.
  2. Move the temperature control from the coldest position to the hottest position and back to the coldest position.

Do you hear the temperature door slam at each end of the door's travel?

Go to Step 2

Go to Step 3

2
  1. Set the mode control to the VENT position.
  2. Set the temperature control to the coldest position.
  3. Start and warm-up the engine.
  4. Record the air temperature at the blower inlet with a thermometer.
  5. Record the air temperature at the vent outlet with a thermometer.

Is the temperature difference 5°C (9°F) or greater?

Go to Step 4

Go to Step 5

3
  1. Inspect the temperature control cable and linkage operation.
  2. Adjust the temperature control cable as necessary. Refer to Temperature Control Cable Replacement .

Is the repair complete?

Go to Step 5

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4
    • Inspect for hot air leaks from the engine compartment to blower air inlet.
    • Inspect the heater case for leaks. Refer to HVAC Module Assembly Replacement .
    • Repair as necessary.

Is the repair complete?

Go to Step 5

--

5

Perform the functional test. Refer to Function Test .

Is the repair complete?

System OK

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