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2008 - MX-5 - HVAC

NO.2 AMOUNT OF AIR BLOWN FROM VENTS DOES NOT CHANGE



2

Amount of air blown from vents does not change.

DESCRIPTION

  • Malfunction in blower system.

POSSIBLE CAUSE

  • Malfunction in A/C unit

  • Malfunction in blower motor

  • Malfunction in power MOS FET system

  • Malfunction in climate control unit


Diagnostic procedure

STEP

INSPECTION

ACTION

1

INSPECT HEATER 40 A FUSE

  • Inspect HEATER 40 A fuse.

  • Is it okay?

Yes

Go to the next step.

No

Replace fuse, then go to Step 15. If fuse burns out immediately, go to the next step.

2

INSPECT TO SEE WHETHER MALFUNCTION IS IN A/C UNIT OR ELSEWHERE

  • Turn ignition switch to ON position.

  • Turn the fan switch to ON position.

  • Recirculate air inside vehicle.

  • Does blower fan rotate smoothly?

Yes

Go to Step 4.

No

Go to the next step.

3

INSPECT AIR DIST UNIT INTAKE VENT

  • Is intake vent of air dist unit clogged?

Yes

Remove obstruction, then go to Step 15.

No

Inspect if there are any obstruction in passage between air dist unit to A/C unit, then go to Step 15.

4*

INSPECT TO SEE WHETHER MALFUNCTION IS IN BLOWER RELAY SYSTEM OR POWER MOS FET SYSTEM

  • Turn ignition switch to ON position.

  • Turn the fan switch to OFF position.

  • Test voltage at the following terminal of blower motor.

    • Terminal B (blower motor operation signal)

  • Is voltage approx. 12 V?

Yes

Go to Step 8.

No

Go to the next step.

5*

INSPECT TO SEE WHETHER MALFUNCTION IS IN WIRING HARNESS (LACK OF CONTINUITY BETWEEN FUSE BLOCK AND BLOWER RELAY) OR ELSEWHERE

  • Test voltage at the following terminal of blower relay.

    • Terminal A (IG2 signal)

    • Terminal C (B+ signal)

  • Is voltage approx. 12 V?

Yes

Go to the next step.

No

Repair wiring harness between blower relay and HEATER 40 A fuse, then go to Step 15.

6*

INSPECT TO SEE WHETHER MALFUNCTION IS IN WIRING HARNESS (LACK OF CONTINUITY BETWEEN BLOWER RELAY AND GROUND) OR ELSEWHERE

  • Test voltage at the following terminal of blower relay.

    • Terminal E (GND signal)

  • Is voltage approx. 0 V?

Yes

Go to the next step.

No

Repair wiring harness between blower relay and ground, then go to Step 15.

7*

INSPECT TO SEE WHETHER MALFUNCTION IS IN WIRING HARNESS (LACK OF CONTINUITY BETWEEN BLOWER RELAY AND BLOWER MOTOR) OR BLOWER RELAY

  • Test voltage at the following terminal of blower relay.

    • Terminal D (blower motor operation signal)

  • Is voltage approx. 12 V?

Yes

Repair wiring harness between blower relay and blower motor, then go to Step 15.

No

Replace blower relay, then go to Step 15.

8*

INSPECT TO SEE WHETHER MALFUNCTION IS IN BLOWER MOTOR OR ELSEWHERE

  • Test voltage at the following terminal of blower motor.

    • Terminal B (blower motor operation signal)

  • Is voltage approx. 12 V?

Yes

Go to the next step.

No

Inspect blower motor, then go to Step 15.

9*

INSPECT TO SEE WHETHER MALFUNCTION IS IN WIRING HARNESS (LACK OF CONTINUITY BETWEEN BLOWER MOTOR AND POWER MOS FET) OR ELSEWHERE

  • Test voltage at the following terminal of power MOS FET.

    • Terminal A (blower motor operation signal)

  • Is voltage approx. 12 V?

Yes

Go to the next step.

No

Repair wiring harness between blower motor and power MOS FET, then go to Step 15.

10*

INSPECT TO SEE WHETHER MALFUNCTION IS IN WIRING HARNESS (LACK OF CONTINUITY BETWEEN POWER MOS FET AND GROUND) OR ELSEWHERE

  • Test voltage at the following terminal of power MOS FET.

    • Terminal D (blower motor operation signal)

  • Is voltage approx. 0 V?

Yes

Go to the next step.

No

Repair wiring harness between power MOS FET and ground, then go to Step 15.

11

INSPECT A/C UNIT

  • Inspect fan in A/C unit.

    • Is fan free of interference with A/C unit case?

    • Is fan free of foreign material and obstruction?

  • Is fan okay?

Yes

Go to the next step.

No

Remove obstruction, repair or replace fan and A/C unit case, then go to Step 15.

12*

INSPECT TO SEE WHETHER MALFUNCTION IS IN POWER MOS FET OR ELSEWHERE

  • Disconnect power MOS FET connector.

  • Turn the fan switch to 1st position from off.

  • Test voltage at the following terminal of power MOS FET.

    • Terminal B (blower motor control signal)

  • Is voltage approx. 10 V?

Yes

Replace power MOS FET, then go to Step 15. (See POWER METAL OXIDE SEMICONDUCTOR FIELD EFFECT TRANSISTOR (POWER MOS FET) REMOVAL/INSTALLATION.)

No

Go to the next step.

13*

INSPECT TO SEE WHETHER MALFUNCTION IS IN WIRING HARNESS (LACK OF CONTINUITY BETWEEN POWER MOS FET AND CLIMATE CONTROL UNIT) OR ELSEWHERE

  • Turn ignition switch to LOCK position.

  • Disconnect climate control unit connector.

  • Inspect for continuity at the following terminals between power MOS FET and climate control unit.

    • Terminal B—E (20-pin, blower motor control signal)

    • Terminal A—C (20-pin, blower motor feedback signal)

  • Is there continuity?

Yes

Go to the next step.

No

Repair wiring harness between power MOS FET and climate control unit, then go to Step 15.

14*

INSPECT TO SEE WHETHER MALFUNCTION IS IN CLIMATE CONTROL UNIT OR WIRING HARNESS (SHORT TO GROUND BETWEEN POWER MOS FET AND CLIMATE CONTROL UNIT)

  • Inspect for continuity at the following terminal between power MOS FET and ground.

    • Terminal B (blower motor control signal)—ground

  • Is there continuity?

Yes

Repair wiring harness between power MOS FET and ground, then go to the next step.

No

Replace climate control unit, then go to the next step. (See CLIMATE CONTROL UNIT REMOVAL/INSTALLATION.)

15

CONFIRM THAT MALFUNCTION SYMPTOMS DO NOT RECUR AFTER REPAIR

  • Is air discharged from vent?

Yes

Troubleshooting completed.

Explain repairs to customer.

No

Recheck malfunction symptoms, then repeat from Step 1 if malfunction recurs.




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