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A/C SYSTEM GENERAL DIAGNOSTIC PROCEDURES
1993 Nissan Sentra
1993 AIR CONDITIONING & HEAT A/C General Diagnostic Procedures Diagnosis is an important first step in A/C system servicing. To save time and effort, systems should be carefully checked to identify the causes of poor performance. By using the following diagnostic charts, defective components or system problems can be quickly located. To identify problems that are specific to one system, refer to the repair section of this manual. The charts in this section apply to all systems. PREPARATION FOR TESTING 1) 2) 3) 4) 5) Attach Low and High pressure gauges. Start engine and allow to warm up. Set system to COOL and blower to HIGH. Open car doors and hood. Run engine at fast idle for 2-3 minutes.
AIR CONDITIONING SYSTEM PERFORMANCE CHECK
AIR CONDITIONING SYSTEM PERFORMANCE CHECK TABLE PERFORM TESTS:
Temperature Check
35-45
PERFORM TESTS: Visual Check
* Compressor
* Condenser
* Receiver-Drier
* Sight Glass
* High Side Lines
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SHOULD BE:
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Quiet with no leaks
Free of obstructions
Dry and warm to touch
Clear or few bubbles
Dry and warm to touch
¢
* Switch to LOW blower. * Close doors. * Check outlet temperature.
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SHOULD BE:
IF:
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F
Temperature Check Is:
Too warm - Check control lever operation, heater water valve, cooling system and gauge readings. IF:
Visual Check Shows:
Noisy - Check belts, oil level, seals, gaskets, reed valves. Blocked - Clean off. Plugged - Flush or replace. Frosty - Check for restriction, replace desiccant. Bubbly, foamy or streaks - Check gauge readings. Frosty or very hot - Check for restriction or overcharge.
* Low Side Lines
Dry and cool to touch
Frosty or warm - Check for restriction, low charge or bad valve. Frosty - Check for moisture or restriction. Check sensing bulb. Frosty or warm - Check gauge readings for valve malfunction. Freezing or warm - Check expansion valve, STV or thermoswitch. IF:
* Expansion Valve
Dry
* STV
Dry and cool to touch
* Evaporator
Dry and cold to touch
PERFORM TESTS: Gauge Readings
* High Side Gauge * Low Side Gauge
Fig. 1:
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SHOULD BE:
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See Pressure Chart See Pressure Chart
Gauge Readings are:
Above or below normal - See A/C Diagnosis. Above or below normal
AMBIENT TEMPERATURE/PRESSURE
Ambient Temperature/Pressure (R-12)
EVAPORATOR TEMPERATURE/PRESSURE
Fig. 2:
Evaporator Temperature/Pressure (R-12)
A/C DIAGNOSIS W/GAUGES FOR SYS. W/INSUFFICIENT OR NO COOLING
A/C DIAGNOSIS W/GAUGES FOR SYS. W/INSUFFICIENT OR NO COOLING TABLE
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Low Side High Side Gauge Gauge Other Symptoms (1) Diagnosis
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HIGH HIGH HIGH HIGH HIGH LOW LOW LOW LOW LOW NORMAL to HIGH NORMAL NORMAL NORMAL NORMAL NORMAL NORMAL NORMAL HIGH HIGH HIGH HIGH LOW LOW LOW LOW LOW LOW Outlet air slightly cool. High side line cool to touch. Sweating or frost on high side. Outlet air warm. Evaporator outlet sweating and frost. Outlet air slightly cool. Bubbles in sight glass. Outlet air warm. Liquid line very hot. Bubbles in sight glass. Noise from compressor. Outlet air slightly cool. Sweating or frost at expansion valve. Sight glass clear. Outlet air very warm. Bubbles in sight glass. Outlet air slightly cool. No or few bubbles in sight glass. High side gauge may go high. Low side gauge does not fluctuate with compressor on/off cycle. Evaporator outlet pipe warm. Outlet air warm. Evaporator outlet pipe cold. Low side goes into vacuum when blower is disconnected. Cycling clutch sys only compressor doesn't turn on soon enough. Discharge air becomes warm as low side pressure rises. Thermostatic sw. sys. onlycompressor cycles off & on too rapidly. Cools okay in morning but not during hot part of day. Bubbles in sight glass. Discharge air warm when low side gauge drops into vacuum. Large Amount of Air of Air & Moisture in System Expansion Valve Stuck Closed Screen Plugged or Sensing Bulb Malfunction Misadjusted Thermostatic Sw. or Defective Pressure Sensing Switch Some Air & Moisture in System Compressor Malfunction or R-12 Overcharge Compressor Malfunction STV Stuck Closed Restriction on High Side Excessively Low R-12 Charge Low R-12 Charge Defective Thermostatic Sw. Excessive Moisture in System STV Stuck Open Expansion Valve Stuck Open
AIR CONDITIONING GENERAL TROUBLE SHOOTING CONDITION & POSSIBLE CAUSE
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * Compressor Not Working Compressor clutch circuit open. Compressor clutch coil inoperative. Poor clutch ground connection. Fan belts loose. Thermostatic switch inoperative. Thermostatic switch not adjusted. Ambient temperature switch open. Superheat fuse blown. Excessive Noise or Vibration Missing or loose mounting bolts. Bad idler pulley bearings. Fan belts not tightened correctly. Compressor clutch contacting body. Excessive system pressure. Compressor oil level low. Damaged clutch bearings. Damaged reed valves. Damaged compressor. Insufficient or No Cooling; Compressor Working Expansion valve inoperative. Heater control valve stuck open. Low system pressure. Blocked condenser fins. Blocked evaporator fins. Vacuum system leak. Vacuum motors inoperative. Control cables improperly adjusted. Restricted air inlet. Mode doors binding. Blower motor inoperative. Temperature above system capacity.
HEATING GENERAL TROUBLE SHOOTING CONDITION & POSSIBLE CAUSE
* * * * * * * * * * * * * Insufficient, Erratic, or No Heat Low coolant level. Incorrect thermostat. Restricted coolant flow through heater core. Heater hoses plugged. Misadjusted control cable. Sticking heater control valve. Vacuum hose leaking. Vacuum hose blocked. Vacuum motors inoperative. Blocked air inlet. Inoperative heater blower motor. Oil residue on heater core fins. Dirt on heater core fins.
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(1) - If equipped with a low refrigerant charge compressor operation may have stopped.
protection system,
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* * * * * * * * * * * * * * * * * *
Too Much Heat Improperly adjusted cables. Sticking heater control valve. No vacuum to heater control valve. Temperature door stuck open. Airflow Changes During Acceleration Vacuum system leak. Bad check valve or reservoir. Air From Defroster At All Times Vacuum system leak. Improperly adjusted control cables. Inoperative vacuum motor. Blower Does Not Operate Correctly Blown fuse. Blower motor windings open. Resistors burned out. Motor ground connection loose. Wiring harness connections loose. Blower motor switch inoperative. Blower relay inoperative. Fan binding or foreign object in housing. Fan blades broken or bent.