HVAC System Symptom Diagnosis: Notes

HVAC SYSTEM SYMPTOM DIAGNOSIS CHART

Condition	Possible Cause	Action
Blower motor does not operate	Blown fuse	Check related fuses, and then check for short circuit to ground .
	Faulty blower motor relay	Check blower motor relay. See CONTROL RELAY INSPECTION
	Faulty blower motor controller	Check blower motor controller. See BLOWER MOTOR CONTROLLER INSPECTION
	Faulty blower motor	Check blower motor. See BLOWER MOTOR INSPECTION
	Faulty wiring or grounding	Repair wiring .
	Faulty HVAC control module	Check HVAC control module. See INSPECTION OF HVAC CONTROL MODULE AND ITS CIRCUIT
	Foreign material is present	Remove foreign material .
No cool air comes out (A/C system does not operate)	No refrigerant	Perform RECOVERY , EVACUATION and CHARGE .
	Blown fuse	Check related fuses, and then check for short circuit to ground .
	Faulty evaporator temperature sensor	Check evaporator temperature sensor. See EVAPORATOR TEMPERATURE SENSOR INSPECTION
	Faulty A/C refrigerant pressure sensor	Check A/C refrigerant pressure sensor. See A/C REFRIGERANT PRESSURE SENSOR AND ITS CIRCUIT INSPECTION
	Faulty wiring or grounding	Repair wiring .
	Faulty ECT sensor	Check ECT sensor. See ECT SENSOR INSPECTION
	Faulty ECM	Check ECM. See A/C SYSTEM INSPECTION AT ECM
	Faulty HVAC control module	Check HVAC control module. See INSPECTION OF HVAC CONTROL MODULE AND ITS CIRCUIT
	Faulty magnet clutch	Check magnet clutch. See A/C COMPRESSOR INSPECTION
	Loosened or broken accessory (A/C compressor) drive belt	Replace drive belt and/or belt tensioner if necessary .
	Faulty A/C compressor	Check A/C compressor .
	Faulty A/C compressor relay	Check A/C compressor relay. See HVAC SYSTEM RELAY INSPECTION
	Faulty auto A/C panel	Replace auto A/C panel .
	Faulty BCM	Check BCM. Refer to INSPECTION OF BCM AND ITS CIRCUITS
No cool air comes out (blower motor does not operate)	Blown fuse	Check related fuses, and then check for short circuit to ground .
	Faulty blower motor controller	Check blower motor controller. See BLOWER MOTOR CONTROLLER INSPECTION
	Faulty HVAC control module	Check HVAC control module. See INSPECTION OF HVAC CONTROL MODULE AND ITS CIRCUIT
	Faulty wiring or grounding	Repair wiring .
	Faulty blower motor	Check blower motor. See BLOWER MOTOR INSPECTION
	Faulty blower motor relay	Check blower motor relay. See HVAC SYSTEM RELAY INSPECTION
Cool air does not come out or insufficient cooling	Insufficient or excessive charge of refrigerant	Check the amount of refrigerant and system for leaks .
	Clogged condenser	Check condenser. See CONDENSER ASSEMBLY ON-VEHICLE INSPECTION
	Clogged or frosted evaporator	Check evaporator and evaporator temperature sensor . Evaporator. See EVAPORATOR INSPECTION Evaporator temperature sensor. See EVAPORATOR TEMPERATURE SENSOR INSPECTION .
	Faulty evaporator temperature sensor	Check evaporator temperature sensor. See EVAPORATOR TEMPERATURE SENSOR INSPECTION
	Faulty A/C refrigerant pressure sensor	Check A/C refrigerant pressure sensor. See A/C REFRIGERANT PRESSURE SENSOR AND ITS CIRCUIT INSPECTION
	Faulty ECM	Check ECM. See A/C SYSTEM INSPECTION AT ECM
	Faulty BCM	Check BCM. See INSPECTION OF BCM AND ITS CIRCUITS
	Faulty expansion valve	Check expansion valve. See EXPANSION VALVE INSPECTION
	Clogged desiccant	Check desiccant .
	Accessory (A/C compressor) drive belt loosened or broken	Replace drive belt and/or belt tensioner if necessary .
	Faulty magnet clutch	Check magnet clutch. See A/C COMPRESSOR INSPECTION
	Faulty A/C compressor	Check A/C compressor .
	Air in A/C system	Replace desiccant, and then perform EVACUATION and CHARGE .
	Air leaking from HVAC unit or air duct	Repair if necessary .
	Faulty heater and ventilation system	Check HVAC unit .
	Faulty auto A/C panel	Replace auto A/C panel .
	Faulty HVAC control module	Check HVAC control module. Refer to INSPECTION OF HVAC CONTROL MODULE AND ITS CIRCUIT
	Faulty temperature control actuator	Check temperature control actuator. See TEMPERATURE CONTROL ACTUATOR INSPECTION
	Faulty wiring or grounding	Repair if necessary .