Automotive Heating Air Conditioning 2 Fixed Orifice Tube

Automotive – Heating & Air Conditioning 2. Fixed Orifice Tube Cycling Clutch System (FOTCC) Topics covered in this presentation: n Basic FOTCC System Components n Basic FOTCC System Operation Class. Act SRS enabled.

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Introduction Air conditioning systems (A/C) used to be only found on high powered luxury vehicles. Today, they are common place, because of engine management systems and advances in A/C control. Two main types: n Thermal Expansion Valve (TXV) System (complex, expensive). Fixed orifice tube n Fixed Orifice Tube Cycling Clutch (FOTCC) System (economical). The TXV system monitors temperature to control the amount of refrigerant sprayed into the evaporator. The FOTCC system monitors pressure to control the amount of refrigerant sprayed into the evaporator. This is performed by switching the compressor on and off (cycling the clutch). Next >

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Question 1 The TXV control of an air conditioning system is not as popular now as the FOTCC method. Why is this? A) TXV is more expensive to produce B) TXV does not offer as good control C) TXV has to be switched on and off frequently D) TXV only works on high powered luxury vehicles

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Basic FOTCC System Components Component and layout used with a FOTCC system: Condenser Evaporator Clutch cycling pressure switch Fixed orifice tube Compressor Suction accumulator Next >

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Question 2 Where is the fixed orifice tube fitted in an air conditioning system? A) Between the clutch pressure switch and the evaporator B) Between the compressor and the condenser C) Between the condenser and the evaporator D) Between the clutch pressure switch and the compressor

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Basic FOTCC System Operation Compressor pumps vapour, creating high and low pressure sides. Air flow through heat exchanger (condenser) Air flow through condenser changes high pressure vapour to liquid. FOTCC valve restricts liquid flow into evaporator. High pressure side Air flow through heat exchanger (evaporator) The low pressure evaporator liquid absorbs heat from vehicle interior and changes back to vapour. Vapour is sucked into accumulator where moisture is removed. Cycle repeats. FOTCC valve Low pressure side Compressor Accumulator Next >

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Question 3 Which of the following sections of an a/c system will be at low pressure? A) Between the compressor and the condenser B) Between the condenser and the fixed orifice tube C) Between the compressor and the fixed orifice tube D) Between the evaporator and the accumulator

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Fixed Orifice Tube Construction Evaporator core Fixed orifice tube High pressure refrigerant liquid Internal diameter of fixed orifice Output filter Input filter Low pressure refrigerant spray O rings Next >

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Fixed Orifice Tube Operation The fixed orifice tube restricts the refrigerant flow. This builds pressure in the condenser and lowers pressure in the evaporator. The fixed orifice tube meters refrigerant flow into evaporator. Fixed Orifice Tube - Incorrect Metering Problems Starved Evaporator Refrigerant flow is too low. It has vapourised before it reaches the evaporator outlet. Cooling is insufficient. Flooded Evaporator Refrigerant flow is too high. There is less vapourisation. Cooling is insufficient. Next >

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Question 4 Which of the following is NOT a function of the fixed orifice tube? A) To restrict the refrigerant flow B) To produce insufficient cooling C) To raise the pressure in the condenser D) To lower the pressure in the evaporator

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Cycling Clutch Pressure Switch Construction Pressure switch controls the system by switching the compressor on and off. Cycling clutch pressure switch Suction accumulator/drier Supply from function selector switch Feed to compressor magnetic clutch field coil Next >

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Question 5 Which property causes the cycling clutch pressure switch to turn on and off? A) Temperature B) Humidity C) Pressure D) Flow rate

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Cycling Clutch Pressure Switch Operation If the A/C system runs continuously, evaporator temperature will drop below freezing and ice will form on the fins, blocking airflow. The switch opens and closes (switches the compressor on and off) in response to refrigerant pressure changes. Typically, it opens at suction pressures below 1. 5 to 1. 7 bar. Typically, it closes at pressures above 3 bar. Next >

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Question 6 Above what pressure, in bar, will a typical cycling clutch pressure switch close? Enter your answer and press SEND.

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Suction Accumulator/Drier Construction Cross section view of a typical accumulator/drier. From evaporator Pressure switch fitting To compressor Plastic cap Vapour return tube Desiccant bag Refrigerant oil Oil filter Next >

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Question 7 What is normally found in the very bottom of a suction accumulator/drier? A) Desiccant B) Vapour C) Water D) Refrigerant oil

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Suction Accumulator/Drier Operation Inlet from Refrigerant from evaporator is mostly vapour, it enters the evaporator drier from the top. Outlet to compressor Plastic cap Vapour swirls round the plastic cap and exits via the vapour return tube. Liquid refrigerant drops to the bottom. Oil mixes with vapour to lubricate system. Vapour return tube Desiccant bag Oil filter Refrigerant oil Next >

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Question 8 Which is the longer tube inside a suction accumulator drier? A) Inlet from evaporator B) Vacuum return tube

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Compressor Clutch Components Compressor Circlip Pulley Lock nut Nut Clutch field coil Bearing Shims Exploded view of the compressor clutch components. Hub Next >

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Compressor Clutch Assembly & Operation Pulley Pin Circlip Coil supply Nut Shims Compressor Coil Lock nut Hub Bearing The clutch field coil locks onto the compressor with a circlip. The clutch pulley is fitted to a bearing on the compressor shaft. Hub is locked onto the compressor shaft with a nut. When engine is started, the pulley rotates. When the field coil is energized, the hub is pulled toward the pulley. They then lock together and the compressor rotates. Next >

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Question 9 What causes the compressor to engage with the hub, when the engine is rotating? A) Energizing the field coil B) Rotating the pulley C) Fitting the clutch pulley D) Locking the hub onto the compressor shaft

2. Fixed Orifice Tube Cycling Clutch System Automotive – Heating & Air Conditioning Summary You should now be aware of: n Basic FOTCC System Components n Basic FOTCC System Operation End >