�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) Attach Low and High pressure gauges. 2) Start engine and allow to warm up. 3) Set system to COOL and blower to HIGH. 4) Open car doors and hood. 5) Run engine at fast idle for 2-3 minutes.

AIR CONDITIONING SYSTEM PERFORMANCE CHECK

AIR CONDITIONING SYSTEM PERFORMANCE CHECK TABLE

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PERFORM TESTS: SHOULD BE: IF:

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Temperature Check			Temperature Check Is:
* Switch to LOW blower. * Close doors. * Check outlet temperature.	35-45 �	F	Too warm - Check control lever
			operation, heater water valve, cooling

system and gauge readings.

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PERFORM TESTS: SHOULD BE: IF:

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Visual Check Visual Check Shows:

*: Sight Glass Clear or few bubbles Bubbly, foamy or streaks - Check gauge readings.
*: High Side Lines Dry and warm to touch 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.
* Expansion Valve	Dry	Frosty - Check for
		moisture or
		restriction. Check
		sensing bulb.
* STV	Dry and cool to touch	Frosty or warm
		- Check gauge
		readings for valve
		malfunction.
* Evaporator	Dry and cold to touch	Freezing or warm
		- Check expansion
		valve, STV or

thermoswitch.

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PERFORM TESTS: SHOULD BE: IF:

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Gauge Readings Gauge Readings are:

*: Low Side Gauge See Pressure Chart Above or below normal

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AMBIENT TEMPERATURE/PRESSURE

Fig. 1: 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

�� _�Low Side _�High Side _�Other Symptoms (1) _�Diagnosis _�Gauge Gauge

�

��_�NORMAL _�NORMAL _�No or few bubbles in sight _�Some Air & Moisture _��glass. High side gauge may _�in System _��go high. Low side gauge _{��}does not fluctuate with _��

_� compressor on/off cycle.

��_�NORMAL _�NORMAL _�Cools okay in morning but _�Excessive Moisture _�

_{_��_�}not during hot part of day. _�in System _��Bubbles in sight glass. _{��}Discharge air warm when low _{��}side gauge drops into _��

_� vacuum.

��_�NORMAL _�NORMAL _�Thermostatic sw. sys. only-_�Defective _�

_{_��_�}compressor cycles off & on _�Thermostatic Sw. _�

_� too rapidly.

��_�NORMAL _�NORMAL _�Cycling clutch sys only -_�Misadjusted _�

_�to _��compressor doesn’t turn on _�Thermostatic Sw. or _��HIGH _��soon enough. _�Defective Pressure _��Discharge air becomes warm _�Sensing Switch _�

_� as low side pressure rises.

��_�LOW _�LOW _�Bubbles in sight glass. _�Low R-12 Charge _�

_� Outlet air slightly cool.

��_�LOW _�LOW _�Sight glass clear. _�Excessively Low _�

_� Outlet air very warm. R-12 Charge

��_�LOW _�LOW _�Outlet air slightly cool. _�Expansion Valve _�

_{_��_�}Sweating or frost at _�Stuck Closed Screen _��expansion valve. _�Plugged or Sensing _�

_� Bulb Malfunction

��_�LOW _�LOW _�Outlet air slightly cool. _�Restriction on _�

_{_��_�}High side line cool to touch. _�High Side _��Sweating or frost on _��

_� high side.

��_�LOW _�HIGH _�Evaporator outlet pipe cold. _�STV Stuck Open _�

_{_��_�}Low side goes into vacuum _� �

_� when blower is disconnected.

��_�HIGH _�LOW _�Evaporator outlet pipe warm. _�STV Stuck Closed _�

_� Outlet air warm.

��_�HIGH _�LOW _�Noise from compressor. _�Compressor _�

_� Malfunction

��_�HIGH _�HIGH _�Outlet air warm. _�Compressor _�

_{_��_�}Liquid line very hot. _�Malfunction _��Bubbles in sight glass. _�or _�

_� R-12 Overcharge

��_�HIGH _�HIGH _�Outlet air slightly cool. _�Large Amount of Air _�

_{_��_�}Bubbles in sight glass. _�of Air & Moisture _�

_� in System

��_�HIGH _�HIGH _�Outlet air warm. _�Expansion Valve _�

_{_��_�}Evaporator outlet sweating _�Stuck Open _�

_� and frost.��

��_�(1) - If equipped with a low refrigerant charge protection system, _�

_� compressor operation may have stopped.��

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.
*: 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.
*: 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.
*: Improperly adjusted cables.
*: Sticking heater control valve.
*: No vacuum to heater control valve.
*: Vacuum system leak.
*: Vacuum system leak.
*: Improperly adjusted control cables.
*: 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.