GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 1998 🢒 DeVille 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 Blower Motor Always On

Circuit Description

The airflow is controlled by modulating the commanded blower voltage. The blower voltage varies the blower speed. The blower is a function of the program number when the blower is under automatic control. Adjustments are made based upon the following factors:

    • The vehicle speed
    • The coolant temperature
    • The sun load sensor

The following special cases may override the normal operation of the blower:

    • Limit snow ingestion
    • Purge the air ducts
    • Cool the instrument panel cluster
    • Enhance the heater warm-up performance

Test Description

If the blower is inoperative in the normal operating procedure, but operates properly in override, the IPC or data line between the IPC and the heater and A/C programmer is suspect.

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check

2
  1. Turn the ignition to the OFF position.
  2. Inspect connector B of the blower motor.

Is battery voltage measured?

B+

Go to Step 3

Go to Step 4

3
  1. Disconnect the blower.
  2. Measure the resistance between connector C and battery voltage. Refer to Testing for Continuity in Wiring Systems.
  3. Measure the resistance between connector A and ground. Refer to Testing for Continuity in Wiring Systems.

Is the resistance greater than the specified value?

1.0 ohms

Go to Step 6

Go to Step 5

4
  1. Inspect CKT 754.
  2. If CKT 754 is OK, replace the heater and A/C programmer. Refer to Programmer Replacement .

Did you complete the repair?

--

Go to Step 8

--

5
  1. Inspect the fuse.
  2. Repair CKT 50 or CKT 542 as required. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 8

--

6
  1. Turn the key to the OFF position.
  2. Measure the resistance between connector B and ground. Refer to Testing for Continuity in Wiring Systems.

Is the resistance less than the specified value?

250K ohms

Go to Step 7

Go to Step 4

7

Replace the blower motor. Refer to Blower Motor and Fan Replacement .

Did you complete the repair?

--

Go to Step 8

--

8
  1. Use the Scan Tool in order to clear the DTCs.
  2. Verify proper operation of the system.

Did you clear the DTCs and verify the operation?

--

Go to Diagnostic System Check

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