Subaru Air Conditioning Systems

Bypass Adjusting Screw (ECVT)

TBI (IAC)

MFI/TBI FICD Operation

Fast Idle Control Device (A/C Idle Air Control)

On manual transaxle equipped Justy vehicles, the FICD is incorporated in the idle-up system. Proper adjustment and operation is outlined in Service Bulletins 02-70-89 and 02-72-89.

On ECVT equipped carbureted vehicles an air/fuel bypass control system performs the FICD function. The ECVT air bypass control system consists of an air bypass valve, an adjusting screw, and an air bypass solenoid. The system is designed to increase idle speed whenever the A/C relay is activated by supplying additional air/fuel into the intake manifold.

Bypass air enters through the air horn on the secondary side.

The airflow is regulated by an adjusting screw. When the bypass valve opens, bypass air/fuel enters the manifold below the secondary throttle plate.

When the adjusting screw is turned clockwise, bypass air/fuel is reduced and the idle speed is lowered. When the adjusting screw is turned counter clockwise, bypass air/fuel is increased and the idle speed is increased.

Note: Always refer to the appropriate Justy model year Subaru Service Manual sections 2-2 and 2-6 for the proper ECVT FICD adjustment procedures and specifications.

TBI system equipped Loyale vehicles control the FICD function through the ECM, the idle air control valve (IAC), and the A/C switch. The air conditioning ON/OFF switch is an input to the ECM. The ECM operates the idle air control valve (IAC) to adjust the idle speed to compensate for the increased compressor load. No adjustment is required.

On all model year Loyale and XT MFI vehicles, an FICD solenoid incorporated in the throttle body provides the increase in idle speed. The throttle body includes an adjustment screw for adjusting the FICD specification.

All Legacy, SVX and XT6 vehicles use an idle air control valve to provide the FICD function. The valve opens a port during A/C operation which admits additional air into the induction system.

Impreza vehicles use a solenoid which initially compensates for the increased compressor load when the air conditioning system is switched ON. The A/C IAC then compensates to maintain engine speed at target RPM.

Note: The Impreza FICD solenoid is set at the factory and should not require adjustment. Any changes to the adjustment can affect driveability and vehicle emissions during cold engine operation.

Justy MFI vehicles increase idle speed by admitting additional air into the air collector assembly through the FICD solenoid which is opened by a signal from the MFI control unit.

End Wrench

The

A/C Idle Air Systems

Impreza FICD

R-12, R-134A specifications

Subaru, a renowned automotive manufacturer, has made significant advancements in its air conditioning refrigerant technologies, particularly in its use of R-12 and R-134A. Understanding these refrigerants is crucial for enthusiasts and technicians alike, as they are integral to Subaru's climate control systems.

R-12, also known as dichlorodifluoromethane, was commonly used in automotive air conditioning systems until the late 20th century. It is a chlorofluorocarbon (CFC) that proved to be highly efficient in cooling systems, offering optimal performance in various conditions. However, environmental concerns over ozone depletion led to a phasedown of its use. Subaru vehicles produced before the early 1990s often utilized R-12, characterized by its stable properties and excellent thermodynamic performance. Despite its effectiveness, the negative environmental impact of R-12 has rendered it obsolete in modern automotive applications.

Adapting to these challenges, Subaru transitioned to R-134A, or tetrafluoroethane, in the 1990s. R-134A is a hydrofluorocarbon (HFC) that does not deplete the ozone layer, making it a more environmentally friendly alternative to R-12. This transition coincided with Subaru's commitment to sustainability and compliance with international regulations. R-134A boasts several advantages, including lower global warming potential and improved efficiency in cooling performance. Its thermodynamic properties provide effective heat absorption, ensuring that Subaru drivers can rely on consistent climate control, regardless of external temperatures.

Subaru has integrated R-134A into its vehicle technology without compromising performance. Newer models utilize advanced HVAC systems that maximize refrigerant efficiency while maintaining comfort. Features such as variable compressor speed control enhance overall system performance, allowing for quicker cooling response and reduced energy consumption. Additionally, Subaru employs meticulous system designs to minimize refrigerant leakage, further supporting environmental initiatives.

The transition from R-12 to R-134A exemplifies Subaru's responsiveness to both performance and environmental concerns. As regulations continue to evolve, it's expected that Subaru will continue to innovate in refrigerant technology, prioritizing sustainability while delivering reliable and efficient climate control for its drivers. As vehicle technology advances, it's clear that Subaru remains committed to adapting its systems for a cleaner, more efficient future.