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DIAGNOSIS & TESTING Mechanical Problems Possible locations or causes of insufficient heat: • An obstructed cowl air intake. • Obstructed heater system outlets. • A blend door not functioning properly. • Trapped air in system. Temperature Control If the heater outlet air temperature cannot be adjusted with the temperature control knob(s) on the A/C heater control • The A/C heater control. • The blend door actuator(s). • The wire harness circuits for the A/C heater control or the blend door actuator(s). • The blend door(s). • Improper engine coolant temperature. A/C Compressor Noise Testing When investigating an A/C system related noise, you must first know the conditions under which the noise occurs. NOTE : NOTE : 1. Select a quiet area for testing. 2. Duplicate the complaint conditions as much as possible. 3. Turn the A/C system On and Off several times to clearly identify any compressor noise. 4. Listen to the A/C compressor while it is operating at maximum and minimum displacement. 5. Probe the A/C compressor with an engine stethoscope or a long screwdriver with the handle held to your ear to better localize the source of the noise. 6. To duplicate high-ambient temperature conditions (high head pressure), restrict the air flow through the A/C con- denser. Install a manifold gauge set or a scan tool to ensure that the discharge pressure does not exceed 2600 7. Check the condition of the accessory drive belt. NOTE: The A/C compressor must be replaced if the drive hub is broken or if the compressor shaft does not 8. Check the compressor hub and pulley and bearing assembly. Ensure that the hub and pulley are properly aligned and that the pulley bearing is mounted securely to the A/C compressor. 9. Check the refrigerant system plumbing for incorrect routing, rubbing or interference, which can cause unusual noises. Also check the refrigerant lines and hoses for kinks or sharp bends that will restrict refrigerant flow, which 10. Loosen all of the compressor mounting hardware and retighten. CAUTION: Do not run the engine with a vacuum pump in operation or with a vacuum present within the 11. If the noise is from opening and closing the high pressure relief valve, recover, evacuate and recharge the refrig- erant system. If the high pressure relief valve still does not seat properly, replace the A/C compressor. 13
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