A/c-Heater System - Automatic: Other Nissan Altima U13

AIR MIX DOOR MOTOR

Air mix door motor is attached to heater unit. Auto amplifier commands air mix door motor to rotate a shaft to move air mix door to a set position/angle. Air mix door position/angle is monitored by Potentiometer Balance Resistor (PBR), located inside air mix door motor. Door position/angle is continuously being fed back to auto amplifier by PBR to allow auto amplifier to move door position/angle for desired temperature.

AMBIENT TEMPERATURE SENSOR

Ambient temperature sensor, located below grille, detects ambient (outside) temperature and converts this reading into a resistance value read by the auto amplifier. (Scheme 25)

If auto amplifier detects an abrupt change, it gradually adjusts interior temperature until desired setting is reached. If vehicle stops in traffic after highway speeds, ambient temperature sensor detects high temperature from heat off radiator. To counteract this sudden temperature change, ambient temperature input process (inside auto amplifier) gradually adjusts interior temperature to prevent unpleasant temperature changes.

ASPIRATOR

Aspirator, located on lower, front of heater unit, produces a vacuum from outlet air discharged from heater unit. This aspirator vacuum pulls air from driver's side area, through in-vehicle temperature sensor.

AUTO AMPLIFIER

The auto amplifier, is a microcomputer that monitors and processes information from various sensors. see scheme 1 Auto amplifier controls air mix door motor, mode door motor, intake door motor, fan motor and compressor clutch operation. Self-diagnostic functions are built into auto amplifier to check A/C-heater system malfunctions.

Auto amplifier detects sensor voltage differences by monitoring an internal, fixed resistor for each sensor. Each sensor is fed 5 volts through the fixed resistor by a constant voltage circuit within auto amplifier. Voltage is then applied to ground through sensor resistance. This signal is the input read by auto amplifier.

BLOWER MOTOR START-UP (COLD SOAK)

If engine coolant temperature is less than 122°F (50°C), the blower motor will not operate for a period of up to 180 seconds. Time delay will vary according to coolant and ambient air temperatures. Under conditions of very low coolant and ambient temperatures, blower motor will begin operating after full delay cycle and operate at low speed. After coolant temperature reaches 122°F (50°C), blower motor speed will increase to objective speed.

BLOWER MOTOR START-UP (HOT SOAK)

If engine coolant temperature is greater than 122°F (50°C), the blower motor will begin operation momentarily after AUTO button is pressed. Blower motor will gradually increase to objective speed over a period of 5 seconds. Time lapse for blower speed increase depends on objective speed.

FAN CONTROL AMPLIFIER

Fan control amplifier, located on evaporator housing, amplifies base current flowing from auto amplifier to fan blower motor. These changes in base current are what changes blower speed. Operating voltage range is from 5-10.5 volts. If auto amplifier senses the need for more than 10.5 volts, high speed relay then applies a direct ground to blower motor for full 12 volts. (Scheme 25)

HIGH SPEED RELAY

High speed relay, located on intake unit, receives its signal from auto amplifier to enable blower motor to operate at high speed. (Scheme 25)

Note. High speed relay may also be referred to as HI relay in TROUBLE SHOOTING charts.

INTAKE DOOR MOTOR

Intake door motor, attached to blower motor unit, is controlled by auto amplifier. (Scheme 25) Motor rotation is transferred by a rod and lever to position intake door for correct air intake.

IN-VEHICLE TEMPERATURE SENSOR

In-vehicle temperature sensor is attached to instrument cluster trim panel. see scheme 1 Driver's area air is drawn through sensor by the aspirator. In-vehicle temperature sensor converts temperature variations to a resistance value, monitored by auto amplifier.

MODE DOOR MOTOR

Mode door motor, attached to heater unit, rotates so air is discharged from outlet(s) controlled by auto amplifier. Motor rotation is transferred by a rod and link to position mode door.

POTENTIOMETER BALANCE RESISTOR (PBR)

This variable resistor is built into air mix door motor and converts air mix door position into a resistance value, monitored by auto amplifier.

Scheme 25

POTENTIOMETER TEMPERATURE CONTROL

Potentiometer Temperature Control (PTC) circuit is built into auto amplifier and is adjustable by temperature control switch. see scheme 1 Temperature can be set in one degree Fahrenheit increments between 65°F (18°C) and 90°F (32°C). Ambient and set temperatures are digitally displayed on auto amplifier.

SUNLOAD SENSOR

Sunload sensor is a photo diode and is located on right defroster grille. Sunlight is converted into a current (voltage) value processed through sunload input process system inside auto amplifier. If sunload input process system detects an abrupt change in sunload sensor input (for example, when vehicle is entering a tunnel), sunload input to auto amplifier will vary for approximately 38 seconds to prevent an unpleasant, quick temperature change by automatic A/C-heater system operation.

AIR MIX DOOR

1. Install air mix door motor onto heater unit and connect wiring harness. (Scheme 25) Enter self-diagnosis step 4 and access Code 41. See «SELF-DIAGNOSIS STEP 4»(ref-35368-S25681604032001010900000) under SELF-DIAGNOSTICS. Move air mix door lever by hand and hold door in full cold setting.
2. Attach air mix door lever to rod holder. Ensure air mix door moves to correct positions when accessing Codes 41-46 by pushing defrost switch. See «SELF-DIAGNOSIS STEP 4»(ref-35368-S25681604032001010900000) under SELF-DIAGNOSTICS.

FRESH VENT DOOR

1. Install fresh vent door motor on intake unit and connect wiring harness. (Scheme 25) Enter self-diagnosis step 4 and access Code 46. See «SELF-DIAGNOSIS STEP 4»(ref-35368-S25681604032001010900000) under SELF-DIAGNOSTICS. Move fresh vent door link by hand and hold fresh vent door in closed setting.
2. Attach fresh vent door lever to rod holder. Ensure fresh vent door moves to correct positions when accessing Codes 41-46 by pushing defrost switch. See «SELF-DIAGNOSIS STEP 4»(ref-35368-S25681604032001010900000) under SELF-DIAGNOSTICS.

INTAKE DOOR

1. Install intake door motor on intake unit and connect wiring harness. (Scheme 25) Enter self-diagnosis step 4 and access Code 41. See «SELF-DIAGNOSIS STEP 4»(ref-35368-S25681604032001010900000) under SELF-DIAGNOSTICS. Move intake door link by hand and hold intake door in recirculate setting.
2. Attach intake door motor rod to intake door link rod holder. Ensure intake door moves to correct positions when accessing Codes 41-46 by pushing defrost switch. See «SELF-DIAGNOSIS STEP 4»(ref-35368-S25681604032001010900000) under SELF-DIAGNOSTICS.

MODE DOOR

1. Install mode door motor onto heater unit and connect wiring harness. (Scheme 25) Enter self-diagnosis step 4 and access Code 46. See «SELF-DIAGNOSIS STEP 4»(ref-35368-S25681604032001010900000) under SELF-DIAGNOSTICS. Move side link by hand and hold mode door in defrost setting.
2. Attach mode door motor rod to side link rod holder. Ensure mode door moves to correct positions when accessing Codes 41-46 by pushing defrost switch. See «SELF-DIAGNOSIS STEP 4»(ref-35368-S25681604032001010900000) under SELF-DIAGNOSTICS.

Air Outlet Does Not Change

1. Set up self-diagnosis step 2. See «SELF-DIAGNOSIS STEP 2»(ref-35368-S18344836212001010900000) under SELF-DIAGNOSTICS. If Code 20 is set, sensor circuits are normal. Go to next step. If any other code(s) is set, check appropriate sensor circuit. See «PRELIMINARY CHECK CODE EXPLANATIONS»(ref-35368-S31324569572001010900000) table. PRELIMINARY CHECK CODE EXPLANATIONS Code (1) Go To 21 Diagnostic Procedure 1 22 Diagnostic Procedure 2 25 Diagnostic Procedure 3 26 Diagnostic Procedure 4 ECON 21 Diagnostic Procedure 1 ECON 22 Diagnostic Procedure 2 ECON 25 Diagnostic Procedure 3 ECON 26 Diagnostic Procedure 4 (1) Before performing DIAGNOSTIC PROCEDURES, ensure temperature detected by each sensor is within normal range. See «SELF-DIAGNOSIS STEP 5»(ref-35368-S34562030202001010900000) under SELF-DIAGNOSTICS.
2. To check mode door motor operation, set up self-diagnosis step 3. See «SELF-DIAGNOSIS STEP 3»(ref-35368-S14070215992001010900000) under SELF-DIAGNOSTICS. If Code 30 is displayed after about 16 seconds, motor is operating correctly. Go to the next step. If Code 30 is not displayed, proceed to «DIAGNOSTIC PROCEDURE 5»(ref-35368-S40357039902001010900000) in TROUBLE SHOOTING section.
3. To check mode door operation, set up self-diagnosis step 4. See SELF-DIAGNOSIS STEP 4 under SELF-DIAGNOSTICS. Check mode door operation under each code. See «MODE DOOR CHECK CODE EXPLANATIONS»(ref-35368-S16939013442001010900000) table. MODE DOOR CHECK CODE EXPLANATIONS Code Door Position 41 Vent 42 (1) B/L (Bi-Level) 43 (2) B/L (Bi-Level) 44 Foot 45 F/D (Foot/Defrost) 46 Defrost (1) 100% recirculated air. (2) 80% recirculated air and 20% fresh air.
4. If mode door operates as specified, air outlet system is okay. If mode door does not function as specified, check side link mechanism. Repair or adjust as necessary. If side link mechanism is okay, go to «DIAGNOSTIC PROCEDURE 5»(ref-35368-S40357039902001010900000) in TROUBLE SHOOTING section.

PRELIMINARY CHECK 2

Note. Perform PRELIMINARY CHECK 1 before proceeding with PRELIMINARY CHECK 2.

Intake Air Does Not Change

1. To check sensor circuit, set up self-diagnosis step 2. See «SELF-DIAGNOSIS STEP 2»(ref-35368-S18344836212001010900000) under SELF-DIAGNOSTICS. If Code 20 is set after about 4 seconds, sensor circuits are normal. Go to next step. If any other code(s) is set, check appropriate sensor circuit. See «PRELIMINARY CHECK CODE EXPLANATIONS»(ref-35368-S31324569572001010900000) table under PRELIMINARY CHECK 1.
2. To check intake door operation, set up self-diagnosis step 4. See «SELF-DIAGNOSIS STEP 4»(ref-35368-S25681604032001010900000) under SELF-DIAGNOSTICS. Check intake door operation under each code. See «INTAKE DOOR CHECK CODE EXPLANATIONS»(ref-35368-S25153249122001010900000) table. INTAKE DOOR CHECK CODE EXPLANATIONS Code Door Position 41 Recirculate 42 Recirculate 43 20% Fresh 44 Fresh 45 Fresh 46 Fresh
3. If intake door operates as specified, air outlet system is okay. If intake door does not function as specified, check intake door rod or lever mechanism. Repair or adjust as necessary. If side rod or lever mechanism is okay, go to «DIAGNOSTIC PROCEDURE 6»(ref-35368-S00263355902001010900000) in TROUBLE SHOOTING section.

Insufficient Cooling

Check operation of components or systems in the order listed. If problem is found, perform checks or repairs as needed before going to next component or system. See INSUFFICIENT COOLING CHECKS table.

INSUFFICIENT COOLING CHECKS

Insufficient Heating

Check operation of components or systems in the order listed. If problem is found, perform checks or repairs as needed before going to next component or system. See INSUFFICIENT HEATING CHECKS table.

INSUFFICIENT HEATING CHECKS

Blower Motor Is Malfunctioning

1. Set up self-diagnosis step 2. See «SELF-DIAGNOSIS STEP 2»(ref-35368-S18344836212001010900000) under SELF-DIAGNOSTICS. If Code 20 is set, sensor circuits are normal. Go to next step. If any other code(s) is set, check appropriate sensor circuit. See «PRELIMINARY CHECK CODE EXPLANATIONS»(ref-35368-S31324569572001010900000) table under PRELIMINARY CHECK 1.
2. To check blower motor operation, set up self-diagnosis step 4. See «SELF-DIAGNOSIS STEP 4»(ref-35368-S25681604032001010900000) under SELF-DIAGNOSTICS. Check for blower motor speed change under each code. See «BLOWER MOTOR CHECK CODE EXPLANATIONS»(ref-35368-S17025814602001010900000) table. BLOWER MOTOR CHECK CODE EXPLANATIONS Code Blower Speed 41 Low 42 Medium High 43, 44 & 45 Medium Low 46 High
3. If blower motor does not test as specified, go to «DIAGNOSTIC PROCEDURE 9»(ref-35368-S02987996532001010900000) in TROUBLE SHOOTING section. If blower motor tests as specified, check coolant and ambient air temperature. If coolant temperature is less than 122°F (50°C) and ambient air temperature is less than 59°F (15°C), go to next step. If temperatures are not as specified, blower motor is operating properly.
4. Check for blower operation under cold soak condition. See «BLOWER MOTOR START-UP (COLD SOAK)»(ref-35368-S13516064792001010900000) under OPERATION. If blower motor does not operate as described, repair thermal transmitter control circuit. If blower motor operates as described, system is okay.

Compressor Clutch Does Not Engage

1. Set up self-diagnosis step 2. See «SELF-DIAGNOSIS STEP 2»(ref-35368-S18344836212001010900000) under SELF-DIAGNOSTICS. If Code 20 is set, sensor circuits are normal. Go to next step. If any other code(s) is set, check appropriate sensor circuit. See «PRELIMINARY CHECK CODE EXPLANATIONS»(ref-35368-S31324569572001010900000) table under PRELIMINARY CHECK 1.
2. To check compressor clutch operation, set up self-diagnosis step 4. See «SELF-DIAGNOSIS STEP 4»(ref-35368-S25681604032001010900000) under SELF-DIAGNOSTICS. Check compressor clutch function under each code. See «COMPRESSOR CLUTCH OPERATION CODE EXPLANATION»(ref-35368-S40994459242001010900000) table. COMPRESSOR CLUTCH OPERATION CODE EXPLANATION Code Clutch Operation 41 On 42 On 43 On 44 Off 45 Off 46 On
3. If compressor clutch engages as specified, system is operating properly. If compressor clutch does not engage as specified, check refrigerant level using gauge manifold. If refrigerant level is low, add refrigerant as necessary. If refrigerant level is okay, go to «DIAGNOSTIC PROCEDURE 10»(ref-35368-S21629876052001010900000) in TROUBLE SHOOTING section.

PRELIMINARY CHECK 7

Note. Perform PRELIMINARY CHECK 1 before proceeding with PRELIMINARY CHECK 7.

Discharged Air Temperature Does Not Change

1. To check sensor circuit, set up self-diagnosis step 2. See «SELF-DIAGNOSIS STEP 2»(ref-35368-S18344836212001010900000) under SELF-DIAGNOSTICS. If Code 20 is set after about 4 seconds, sensor circuits are normal. Go to next step. If any other code(s) is set, check appropriate sensor circuit. See «PRELIMINARY CHECK CODE EXPLANATIONS»(ref-35368-S31324569572001010900000) table under PRELIMINARY CHECK 1.
2. To check air mix door operation, set up self-diagnosis step 4. See «SELF-DIAGNOSIS STEP 4»(ref-35368-S25681604032001010900000) under SELF-DIAGNOSTICS. Check air mix door operation under each code. See «AIR MIX DOOR CHECK CODE EXPLANATIONS»(ref-35368-S17702993192001010900000) table. AIR MIX DOOR CHECK CODE EXPLANATIONS Code Door Position 41 & 42 Full Cold 43-46 Full Hot
3. If air mix door operates as specified, air outlet system is okay. If intake door does not function as specified, check air mix door mechanism. Repair or adjust as necessary. If mechanism is okay, go to «DIAGNOSTIC PROCEDURE 7»(ref-35368-S42609892172001010900000) in TROUBLE SHOOTING section.

Preliminary Information

During all self-diagnostic functions, ensure fresh vent switch on auto amplifier is in off position, unless otherwise indicated. see scheme 1 To properly diagnose this system, self-diagnostics should be performed in the following order

1. Read «ENTERING/EXITING SELF-DIAGNOSTICS»(ref-35368-S12912589502001010900000) .
2. Perform SELF-DIAGNOSIS STEPS 1-5.
3. Refer to appropriate PRELIMINARY CHECK in TROUBLE SHOOTING for symptom diagnosis. Preliminary checks refer technician to proper DIAGNOSTIC PROCEDURE charts in TROUBLE SHOOTING section.

Checks Light Emitting Diodes (LEDs) & Segments

Step 1 starts automatically when self-diagnostics are entered. All LEDs and fluorescent display tubes should illuminate. see scheme 1 If all LEDs and fluorescent display tubes DO NOT illuminate, OFF switch is malfunctioning or LED or fluorescent tube is defective. Repair or replace as necessary. If OFF switch, LEDs and fluorescent display tubes test okay, replace auto amplifier.

Checks Sensor Circuits For Open/Short Circuits

1. Position vehicle to enable sunlight to shine on sunload sensor. Enter self-diagnosis step 2 by pressing temperature switch up arrow on auto amplifier. see scheme 1
2. Display will illuminate a 2. If all sensor circuits are okay and no trouble codes are present, display will change to Code 20. It takes auto amplifier about 4 seconds to check all sensor circuits.
3. If a sensor circuit is faulty, circuit code number will flash on display. If circuit is shorted, ECON LED, located next to displayed code will blink. If circuit is open, ECON LED will not blink. If, for example, 21 is displayed on auto amplifier by an illuminated 21 and a flashing ECON LED, a short circuit is indicated.
4. If two sensor circuits are faulty, each circuit code number will blink twice. See «SELF-DIAGNOSIS STEP 2 CODE EXPLANATIONS»(ref-35368-S42689309042001010900000) table to determine what a code number means.

SELF-DIAGNOSIS STEP 2 CODE EXPLANATIONS

Checks Mode Door Position

1. To enter self-diagnosis step 3, press temperature switch up arrow on auto amplifier. see scheme 1 Display will illuminate a 3. If all doors are operational, display will change to 30. It takes about 16 seconds to check all mode doors.
2. If a door is faulty, code number will flash. If two doors are faulty, each code number will blink twice. To determine what a code number means, see «SELF-DIAGNOSIS STEP 3 CODE EXPLANATIONS»(ref-35368-S03876277062001010900000) table.

Note. If any mode door motor position switch is malfunctioning, mode door motor will also malfunction.

SELF-DIAGNOSIS STEP 3 CODE EXPLANATIONS

Checks Temperature Detected By Sensors

1. To enter self-diagnosis step 5, press temperature switch up arrow on auto amplifier. Display will illuminate a 5. When defrost switch is pressed once, display will show temperature detected by ambient temperature sensor.
2. Press defrost switch again (2nd time), display will show temperature detected by in-vehicle sensor.
3. Press defrost switch again (3rd time), display will return to 5. If temperature shown on display is greatly different from actual temperature, inspect sensor circuit. If sensor circuit is okay, check sensor. See appropriate sensor under «TESTING»(ref-35368-S25487133412001010900000) .

Temperature Setting Trimmer

1. Temperature setting trimmer compensates for small differences between temperature setting on display and actual temperature within a range of 0-12°F (0-6°C).
2. With system in «SELF-DIAGNOSIS STEP 5»(ref-35368-S34562030202001010900000) , press fan switch. System is now in auxiliary mode to set trimmer. Each time temperature switch up or down arrow is pressed, temperature display changes in one degree Fahrenheit increments.

Note. If battery is disconnected, temperature trimmer setting goes to 0° on both Fahrenheit and Celsius scale and will have to be reset.

A/C SYSTEM PERFORMANCE

1. Park vehicle out of direct sunlight. Close all doors and open engine hood and windows. Connect A/C pressure gauges to the high and low side pressure ports of system. Disconnect ambient temperature sensor connector.
2. Ambient temperature sensor is located below hood latch. Connect a jumper wire between sensor connector terminals. Determine relative humidity and ambient air temperature.
3. Set temperature control to maximum cold, mode control to vent (face), and recirculation switch to recirculated air position. Turn blower fan switch to highest speed setting. Start and run engine at 1500 RPM.
4. After running A/C for 10 minutes, check high and low side system pressures. Refer to «A/C SYSTEM PERFORMANCE TEST»(ref-35368-S12358683202001010900000) table to determine if system is operating within range.

A/C SYSTEM PERFORMANCE TEST

Turn ignition off. Disconnect underhood ambient temperature sensor connector, in front of condenser, near hood latch. (Scheme 25) Using an ohmmeter, measure resistance between sensor terminals. See AMBIENT & IN-VEHICLE TEMPERATURE SENSORS SPECIFICATIONS table.

Turn ignition off. Disconnect in-vehicle temperature sensor connector. (Scheme 25) Using an ohmmeter, measure resistance between sensor terminals. Refer to the AMBIENT & IN-VEHICLE TEMPERATURE SENSORS SPECIFICATIONS table.

AMBIENT & IN-VEHICLE TEMPERATURE SENSORS SPECIFICATIONS

1. Turn ignition on. Backprobe air mix door motor connector with voltmeter and measure voltage between terminals No. 27 (Pink/Blue wire) and No. 33 (Pink wire). see scheme 3 Set temperature switch to coldest setting. With air mix door in full cold position, voltmeter should indicate zero volts.
2. Slowly adjust temperature switch to hottest setting. As air mix door motor moves from full cold to full hot position, voltage should slowly rise to 5 volts. If voltage is not as described, replace air mix door motor.

Scheme 26

1. Turn ignition off. Backprobe auto amplifier connector with voltmeter and measure output voltage between terminals No. 26 (Orange wire) and 38 (Black/Yellow wire). To vary voltage reading for testing, apply direct sunlight to sensor, then slowly cover sensor.
2. To measure sunload sensor input to auto amplifier, disconnect sensor from vehicle harness above intake unit. Connect an ammeter between sensor connector terminals. To vary current reading, apply direct sunlight to sensor, then slowly cover the sensor. See «SUNLOAD SENSOR SPECIFICATIONS»(ref-35368-S32911756642001010900000) table.

SUNLOAD SENSOR SPECIFICATIONS