Nissan 240SX 1990 A/C Heater System PDF Manual Installation Instructions

Desired air control mode is achieved by push buttons, turn- dial or lever-type controls on A/C-heater control panel. Air intake control can be set for RECIR (recirculated) or OUTSIDE air entry. A/C switch and fan controls are independent of mode controls. See Fig. 1. System operation for lever-type control panel are as follows: VENT/RECIR Mode; A/C OFF, Fan ON; COLD Temp. Setting Recirculated air discharged through dashboard outlets. No outside air entry. No temperature variation. Heater control valve closed. VENT/RECIR Mode; A/C ON; Fan ON; COLD Temp. Setting Air discharged (recirculated) at cold temperature.

Heater control valve closed. Fast idle actuator on. Air discharged through dashboard outlets. VENT/OUTSIDE Mode; A/C OFF; Fan ON Outside air drawn in. Heater control valve closed. Fast idle actuator off. Discharged air temperature same as outside air. Air discharged through dashboard outlets. BI-LEVEL/OUTSIDE Mode; A/C OFF; Fan ON Outside air drawn in. Floor and dashboard outlet air is warm- to-cool, depending on temperature lever setting. Heater control valve open-to-closed, depending on temperature lever setting. HEAT/OUTSIDE Mode; A/C OFF; Fan ON; HEAT Temp. Setting Outside air drawn in. Floor outlet air warm-to-cool, depending on temperature lever setting. Heater control valve open, depending on temperature lever setting. If equipped, a fresh air ventilation lever may be pushed to allow outside cool air to face-vent outlets while still allowing heated air to floor outlets. DEF/OUTSIDE Mode; A/C OFF; Fan ON; HEAT Temp. Setting Outside air drawn in. Defroster outlet air cool-to-warm, depending on temperature lever setting. Heater control valve open, depending on temperature lever setting. A/C compressor operates intermittently to stabilize interior windshield air temperature and reduce fogging of windshield.

CONDENSER & COOLING FAN RELAYS Condenser and radiator cooling fan relays have Blue outer case and are located within engine compartment relay boxes. Condenser fan is controlled through A/C relay. Typical system consists of condenser and radiator cooling fans controlled by 3 relays. Relay No. 1 is used low-speed operation, while relay No. 2 and relay No. 3 are for high-speed operation. Relay grounds are controlled by Engine Concentrated Control System (ECCS). HIGH & LOW PRESSURE CUT-OFF SWITCH The high and low (dual) pressure cut-off switch, normally mounted on receiver-drier, protects A/C system from high pressure build-up (due to restriction, overcharge or compressor malfunction). If excessively low or high system pressure is sensed, the switch electrically stops compressor clutch operation.

A high pressure/temperature relief valve is mounted on receiver-drier. When high pressure of 540 psi (38 kg/cm ) or temperature of 210 F (105 C) is sensed, relief valve opens, venting refrigerant to atmosphere. THERMO CONTROL UNIT An electrical thermo control unit is mounted on evaporator housing. A temperature sensor (thermistor), inside evaporator housing, senses air temperature and sends signal to thermo control unit. Thermo control unit then cycles compressor clutch on and off, according to temperature lever setting on control panel. ACCELERATION CUT SYSTEM This system monitors vacuum pressure in intake manifold. When engine is under heavy loaded (low vacuum condition), A/C compressor is turned off for 5 seconds to reduce engine load. FAST IDLE CONTROL DEVICE (FICD) When A/C system is energized, the engine control module signals FICD to adjust Auxiliary Air Control (AAC) valve to bypass additional air and increase idle speed. This higher idle speed allows engine to idle smoothly during compressor operation. THERMAL PROTECTOR SWITCH The thermal protector switch, installed in A/C compressor at evaporator refrigerant line inlet, incorporates a pressure diaphragm switch and temperature sensor. When refrigerant temperature increases, temperature sensitive gas inside temperature sensor expands, causing diaphragm switch to open electrical circuit to A/C compressor. SERVO MOTORS Electric servo motors control intake air, air mode and air mix doors to distribute conditioned air to passenger compartment. ADJUSTMENTS NOTE: For control cable and door rod adjustments, see HEATER SYSTEMS article. TROUBLE SHOOTING NOTE: See MANUAL A/C-HEAT TROUBLE SHOOTING article in this section. TESTING FAN SWITCH To check fan switch for proper operation, check for continuity between switch terminals. See Fig. 2.

Download Nissan 240SX 1990 A/C Heater System PDF Manual Installation Instructions