HEAT, VENTILATION & A/C 1986 Manual A/C-Heater Systems (2024)

A/C SYSTEM SPECIFICATIONS

A/C SYSTEM SPECIFICATIONS

DESCRIPTION

System combines air conditioning and heating unit. The A/C system consists of evaporator assembly, compressor, condenser, receiver-drier and electrical components in addition to the standard heating unit. Air door operation is controlled through cable connections, while compressor operation and associated A/C modes are electrically controlled. A thermistor is used to sense evaporator temperature, and an idle stabilizer amplifier controls compressor on and off function.

OPERATION

SYSTEM CONTROL PANELS

Pickup

Pickup uses 3 sliding levers to control mode selection, air temperature and air supply selection (fresh or recirculating air). A combination blower switch knob and A/C thermostat control are used. Turning A/C switch varies resistance signal to amplifier, which changes necessary operation of compressor clutch.

SYSTEM COMPONENTS

A/C Thermo Control Switch (Pickup)

Rotating the switch changes resistance value sent to amplifier. Amplifier then changes on-off cycling pattern of compressor clutch to accommodate change in setting (temperature). When rotated all the way to the right, the switch provides maximum cooling.

Pressure Switch

A low pressure protection switch is used to stop compressor clutch operation in the event of loss of R-12 pressure charge. Switch is installed in the high side line inside evaporator housing. Switch diaphragm holds contact points in the switch closed above 30 psi, completing the circuit to compressor. At pressures below 30 psi, the contacts open and the circuit to compressor is interrupted.

Thermistor

The thermistor is a thermocouple mounted in front of the evaporator (air outlet side) to sense the temperature of air flow. The value of thermistor is sent to amplifier. The amplifier then sends appropriate electrical signal to compressor clutch for proper on-off cycling.

Idle Stabilizing Amplifier

This unit receives electrical values from the thermistor and distributor (engine speed). When these values are compared, a signal is sent to compressor clutch to control on and off operation. By using both engine speed and A/C temperature as its values, amplifier can attain suitable compressor operation.

Engine speed sensing allows compressor operation only after a certain engine RPM has been reached. This prevents rough idle and engine overheat which may occur with compressor running at idle. Amplifier also prevents evaporator freeze-up by cutting off compressor operation when low temperature signal is sent from thermistor. Amplifier is mounted on lower half of evaporator housing.

Vacuum Switching Valve

An electro-vacuum (solenoid) valve is used to assist in smooth engine operation during compressor on cycle. See Fig.1 and Fig.2. The vacuum switching valve (VSV) holds the throttle at slightly above idle (spring-loaded to this position) when A/C system is operating. When system is off, vacuum is directed to VSV diaphragm to allow throttle to return to normal idle position.

Fig. 1: Schematic of Vacuum Switching Valve (A/C Off)

Fig. 2: Schematic of Vacuum Switching Valve (A/C On)

ADJUSTMENTS

IDLE STABILIZING AMPLIFIER

Amplifier has 2 adjusting screws. See Fig.3. This permits adjustment of the engine RPM cut-out points for compressor operation, and permits adjustment of temperature resistor on vehicles equipped with a thermostat. Adjust RPM to 600-700 RPM

Adjustment

1. To adjust engine RPM cut-out points, turn knob on side of amplifier clockwise to reduce RPM point, or counterclockwise to increase RPM point.
2. To adjust temperature, turn adjusting screw clockwise to reduce temperature or counterclockwise to raise temperature. Clutch engagement and disengagement should also correspond to the settings listed.

TEMPERATURE CIRCUIT RESISTANCE SPECIFICATIONS

Fig. 3: Idle Stabilizing Amplifier Adjusting Screw Locations
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

TESTING

A/C SWITCH

Disconnect battery. Remove left side air duct and ashtray. Disconnect A/C switch connector. Test for continuity at terminals.

A/C SWITCH CONTINUITY

Fig. 4: Testing for Continuity of A/C Switch
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

CONDENSER FAN & IDLE UP RELAYS

Fig. 5: Condenser Fan Relays Location

Fan Relay No. 1

Using ohmmeter, check for continuity between terminals No. 3 and No. 4. If there is no continuity, replace relay. Apply battery voltage between terminals No. 1 and No. 2. Check for continuity between terminals No. 3 and No. 4. If there is no continuity, relay is okay. If there is continuity, replace relay.

Fig. 6: Checking Condenser Fan Relay No. 1

Fan Relay No. 2

Using ohmmeter, check for continuity between terminals No. 1 and No. 4. If there is continuity, replace relay. If there is no continuity, relay is okay. Apply battery voltage between terminals No. 6 and No. 2. Check for continuity between terminals No. 1 and No. 4. If there is continuity, relay is okay. If there is no continuity, replace relay.

Fig. 7: Checking Condenser Fan Relay No. 2

Idle Up & Fan Relay No. 3

Using ohmmeter, check for continuity between terminals No. 2 and No. 4. If there is no continuity, relay is okay. If there is continuity, replace relay. Apply battery voltage between terminals No. 1 and No. 3. Check for continuity between terminals No. 2 and No. 4. If there is continuity, relay is okay. If there is no continuity, replace relay.

Fig. 8: Checking Condenser Fan Relay No. 3

A/C CUT RELAY

Using an ohmmeter, check for continuity between terminals No. 3 and No. 4. If there is no continuity, replace relay. Apply battery voltage between terminals No. 1 and No. 2. Check for continuity between terminals No. 3 and No. 4. If there is continuity, replace relay. If there is no continuity, relay is okay.

Fig. 9: Checking A/C Cut Relay

THERMISTOR

1. Disconnect battery. Remove instrument panel lower trim and glove box. Separate thermistor from evaporator core. Dip thermistor into container of ice water.
2. Connect ohmmeter leads to thermistor connector. See Fig.10. While measuring the ambient temperature, measure resistance of the thermistor as shown. Vary surrounding temperature and take another reading. See Fig.11. If not within given range, replace thermistor.

Fig. 10: Testing Resistance of Thermistor

Fig. 11: Thermistor Resistance Graph

IDLE STABILIZING AMPLIFIER

Operate system, measuring cut-off points of compressor and clutch according to engine speed and temperature of outlet air. See SPECIFICATIONS under ADJUSTMENTS in this article. If system not operating as noted, adjust amplifier. If proper adjustments cannot be made, replace amplifier.

VACUUM SWITCHING VALVE

1. With valve on car, remove vacuum connections from both fittings on VSV. See Fig.12. Connect VSV terminal connector to battery. Blow air through fitting "A". Air should pass from "A" and out through "B". It should not be felt at atmospheric port.
2. Disconnect battery from VSV terminal connector. Blow air through fitting "A". It should pass from "A" and come out atmospheric port. It should not come out fitting "B".
3. Use an ohmmeter to check for short between each terminal and VSV body. Also check resistance between the 2 terminals. Reading should be 38-43 ohms at 68°F (20°C).

Fig. 12: Testing Vacuum Switching Valve

PRESSURE SWITCH

1. Use manifold gauge set to check R-12 pressures. If high side is above 30 psi, pressure switch should keep electrical circuit to compressor completed. If not, test as described.
2. Remove glove box and lower trim. Disconnect leads from pressure switch. Using an ohmmeter, check continuity between terminals. Reading should be zero. If not, replace pressure switch.

TROUBLE SHOOTING

Failure of thermistor or of idle stabilizing amplifier will cause failure of system to operate at all, or to produce little or no cooling in the system. Check other basic system components first before determining these electrical items to be defective.

REMOVAL & INSTALLATION

COMPRESSOR

Removal

1. If possible, run system for more than 10 minutes before beginning removal. Disconnect battery. Detach magnetic clutch wire from A/C harness. Discharge A/C system using approved refrigerant recovery/recycling equipment.
2. Detach A/C hoses from service valves. Plug all openings. Loosen and remove compressor belt from pulley. Remove compressor mounting bolts and remove compressor.

Installation

To install, reverse removal procedure. Evacuate, recharge and leak test system.

EVAPORATOR ASSEMBLY

Removal

1. Disconnect battery. Discharge A/C system using approved refrigerant recovery/recycling equipment. Detach inlet and outlet lines and grommets from evaporator. Plug openings.
2. Disconnect electrical leads from evaporator. Remove glove box and lower trim panel. Remove side air duct. Remove nuts and bolts and remove evaporator assembly.

Disassembly

1. Remove thermistor. Release spring clips holding covers together. Remove any screws at case joints. Separate upper and lower cases from evaporator core. Remove idle stabilizing amplifier from lower case.
2. Remove heat insulator from outlet tube. Remove high side (inlet) line from expansion valve and remove expansion valve. Remove pressure switch.

Reassembly & Installation

Reverse disassembly and removal procedure. If installing new evaporator core, add 1.4-1.7 oz. of refrigerant oil to core prior to installation. Evacuate, recharge and leak test system.

Fig. 13: Exploded View of Camry EVAP Assembly (P/U & 4Runner Sim.
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

CONDENSER

Removal

1. Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove grille and hood lock brace. Remove lower engine cover, if equipped. Detach A/C lines from condenser. Plug all openings. Remove tube clip.
2. Detach condenser fan motor connector. Remove mounting bolts and take out condenser.

Installation

Reverse removal procedure to complete installation. If installing new condenser, add 1.4-1.7 oz. of refrigeration oil before installation. Evacuate, recharge and leak test system. Repeat if necessary.

RECEIVER-DRIER

Removal

Discharge A/C system using approved refrigerant recovery/recycling equipment. Remove A/C lines from receiver-drier. Plug all openings. Remove mounting bolts and take out receiver-drier.

Installation

To complete installation, reverse removal procedure. Add 0.7 oz. of refrigerant oil. Evacuate, recharge and leak test system.

EXPANSION VALVE

Evaporator must be removed to remove expansion valve. See REMOVAL & INSTALLATION - EVAPORATOR ASSEMBLY procedure in this article.

PRESSURE SWITCH

Evaporator assembly must be removed to remove pressure switch. See REMOVAL & INSTALLATION - EVAPORATOR ASSEMBLY procedure in this article.

WIRING DIAGRAMS

Fig. 14: Manual A/C-Heater Systems Wiring Diagram (Exc. Turbo)

Fig. 15: Manual A/C-Heater Systems Wiring Diagram (Turbo)