ASE S7 Air Conditioning Systems & Controls (School Bus) key terms

The process of removing refrigerant from a system and storing it in an external container without necessarily testing or processing it, so it can be reused or sent for reclamation.

Cleaning recovered refrigerant by removing oil, moisture, and particulates so it meets a specified purity standard and can be returned to the same vehicle or equipment.

A refillable, DOT-approved pressure vessel used to hold recovered refrigerant; it must never be filled beyond 80 percent of its capacity by liquid volume.

The EPA credential required for technicians who service or repair motor vehicle air conditioning systems; it covers refrigerant handling rules under the Clean Air Act.

The Clean Air Act rule that bans knowingly releasing refrigerant to the atmosphere during service, repair, or disposal of motor vehicle air conditioning systems.

A component in recovery or recycling equipment that removes water from refrigerant, since moisture forms corrosive acids and can freeze at the expansion device.

A canister on the high side of a system that stores liquid refrigerant and holds desiccant to absorb moisture and filter debris before the refrigerant reaches the expansion device.

A canister on the low side of an orifice-tube system that traps liquid refrigerant so only vapor returns to the compressor, and also holds desiccant to absorb moisture.

A thermostatic valve that meters refrigerant into the evaporator and regulates flow by sensing outlet temperature or pressure to maintain proper superheat.

A fixed-restriction metering device with a calibrated passage that controls refrigerant flow into the evaporator; system capacity is managed by cycling the compressor.

The number of degrees a refrigerant vapor is above its saturation temperature at a given pressure; used to judge whether an expansion valve is feeding the evaporator correctly.

The number of degrees a liquid refrigerant is below its saturation temperature at a given pressure; used to judge charge level and condenser performance on the high side.

An electromagnetic assembly that engages or disengages the compressor pulley from the drive belt in response to a control signal, allowing the system to cycle on demand.

The electromagnetic winding inside the compressor clutch that, when energized, creates a magnetic field pulling the armature plate against the pulley to drive the compressor.

A sensor that opens or closes an electrical circuit based on refrigerant pressure, used to protect the compressor or cycle it for temperature control.

A pressure switch with two functions, typically cutting the compressor clutch at dangerously low or high pressures to protect the system from damage.

A three-function pressure switch that protects against low and high pressure and also controls the condenser cooling fan at elevated discharge pressure.

The heat exchanger mounted at the front of the vehicle that releases heat from high-pressure refrigerant vapor, causing it to condense into a liquid.

An electric or belt-driven fan that pulls air through the condenser to remove heat, especially important at low vehicle speed or when the bus is stopped.

The heat exchanger inside the passenger compartment where low-pressure liquid refrigerant absorbs heat from the air and boils into vapor, cooling and dehumidifying the air.

An electric motor that drives the blower wheel to move air across the evaporator and through the ductwork; speed is set by resistors or a control module.

A set of resistive elements that reduces voltage to the blower motor to provide lower fan speeds; an open resistor commonly causes loss of some speeds.

A movable flap in the HVAC case that mixes or diverts air through the heater core to control outlet temperature.

An electric motor or vacuum motor that moves the blend door in response to a control head command or automatic temperature control signal.

A door in the air distribution case that directs conditioned air to the floor, panel, or defrost outlets according to the driver's selection.

A small radiator inside the HVAC case through which engine coolant flows; air passing over it is warmed for cabin heat and windshield defrosting.

The HVAC mode that directs dehumidified, warmed air onto the windshield to clear fog and frost; most systems run the compressor in this mode.

A system that uses sensors and a control module to automatically adjust blend door position, blower speed, and compressor operation to hold a set cabin temperature.

A sensor, often aspirated by a small fan, that measures cabin air temperature and feeds the reading to the automatic temperature control module.

A sensor that reports outside air temperature to the control module, used for A/C strategy decisions and driver display.

A tool with high-side and low-side gauges and service hoses used to read system pressures and connect recovery or charging equipment to the service ports.

A Schrader-valve fitting on the high or low side of the system where gauges, recovery equipment, or charging hoses are connected.

The process of finding refrigerant leaks using electronic detectors, UV dye, soap bubbles, or pressure testing, required before recharging a low system.

Lubricant such as PAG or POE that circulates with refrigerant to lubricate the compressor; the correct type and quantity must be maintained during service.

The belt that transfers engine power to the compressor pulley and other accessories; tension and alignment are critical to prevent slippage and clutch wear.

A device that analyzes refrigerant in a cylinder or system to confirm its type and purity, preventing cross-contamination during recovery or recharge.

Mixing different refrigerants or introducing air and moisture into a system, which degrades performance, damages equipment, and requires costly cleanup.