(VDOT) Refrigeration System
The Variable Displacement Orifice Tube (VDOT) refrigeration system has a V5 compressor. The V5 compressor used on the 3400 engine can match the automotive air conditioning demand under any conditions without cycling.The basic compressor mechanism is a variable angle wobble-plate with five axially oriented cylinders.
A bellows actuated control valve determines the compressor displacement. This control valve is located in the rear head of the compressor, and senses the suction pressure of the compressor.
The crankcase suction pressure differential controls the following:
^ The wobble-plate angle
^ The compressor displacement
The following actions occur when the A/C capacity demand is high:
^ The suction pressure is above the control point.
^ The valve maintains a bleed from the crankcase to suction.
^ No crankcase-suction pressure differential exists.
^ The compressor has maximum displacement. The following actions occur when the A/C capacity demand is lower and the suction pressure reaches the control point:
^ The valve bleeds discharge gas into the crankcase.
^ The valve closes off a passage from the crankcase to the suction plenum.
A force balance on the five pistons controls the angle of the wobble plate. A slight increase of the crankcase-suction pressure differential changes the total force on the pistons. This change affects the movement around the wobble-plate pivot pin and reduces the angle of the wobble plate.
The compressor has a unique lubrication system. The crankcase-suction bleed is routed through the rotating wobble-plate. This routing permits lubrication of the wobble-plate bearing. The rotation acts as an oil separator. Some of the oil is removed from the crankcase-suction bleed and rerouted to the crankcase. The rerouted oil can lubricate the compressor mechanism.
The compressor is cut off when the following conditions exist:
^ Wide-open throttle
^ Low idle speed
^ Low air temperature
^ High power steering loads
The refrigerant in the system flows from the high pressure side to the low pressure side of the expansion (orifice) tube when the following conditions exist:
^ The engine is turned off.
^ The A/C system is operating.
The refrigerant continues to flow until the pressure is equalized. This action may cause a faint sound of liquid flowing (hissing) for 30 to 60 seconds. The sound is a normal condition.
Refrigerant-134a
Caution: Avoid breathing the A/C Refrigerant 134a (R-134a) and the lubricant vapor or the mist. Exposure may irritate the eyes, nose, and throat. Work in a well ventilated area. In order to remove R-134a from the A/C system, use service equipment that is certified to meet the requirements of SAE J 2210 (R-134a recycling equipment). If an accidental system discharge occurs, ventilate the work area before continuing service. Additional health and safety information may be obtained from the refrigerant and lubricant manufacturers.
The refrigerant performs a function which is similar to the engine coolant. The refrigerant is the medium within the A/C system that performs the following functions:
^ Absorbs heat
^ Carries heat
^ Releases heat
Although various substances are used as refrigerants in other types of refrigeration systems, past automotive air conditioning systems used a type of fluid called Refrigerant-12 (R-12). This vehicle uses a new type of refrigerant which is called Refrigerant-134a (R-134a). R-134 is a liquefied gas which has the following properties:
^ Non-toxic
^ Non-flammable
^ Clear
^ Colorless
The R-134a A/C system is very similar to an R-12 A/C system. However, the differences in the following components are important:
^ The refrigerant
^ The lubricants
^ The service equipment
Notice: R-12 refrigerant and R-134a refrigerant must never be mixed, even in the smallest of amounts, as they are incompatible with each other. If the refrigerants are mixed, compressor failure is likely to occur. Refer to the manufacturer instructions included with the service equipment before servicing.
Notice: Use only Polyalkylene Glycol Synthetic Refrigerant Oil (PAG) for internal circulation through the R-134a A/C system and only 525 viscosity mineral oil on fitting threads and O-rings. If lubricants other than those specified are used, compressor failure and/or fitting seizure may result.
Muffler
A muffler is used on some refrigerant systems in order to reduce the following conditions:
^ Compressor noises
^ High-pressure-line vibrations
Thermal Expansion Valve Description
The thermostatic expansion valve regulates the flow of refrigerant through the evaporator in order to optimize the evaporator's cooling performance. This assures that all of the liquid is evaporated before the refrigerant is returned to the compressor. The thermostatic expansion valve accomplishes this by performing the following functions:
1. Monitoring the refrigerant conditions at the evaporator outlet
2. Adjusting the inlet flow accordingly
The movement of the shaft pushes a ball. The ball controls the refrigerant flow. As the ball is unseated, more flow is allowed through the evaporator. The power dome controls the shaft movement. The power dome has two separate sides (1,2). The thermal side of the power dome is sealed and charged with refrigerant. The system side of the power dome is exposed to the pressure of the evaporator outlet or lower side. The sealed refrigerant in the thermal side responds to the temperature changes of the refrigerant that is flowing out of the evaporator. As the refrigerant temperature rises, the pressure of the thermal side increases.
If the pressure on the thermal side of the power dome is greater than the pressure on the system side (the evaporator outlet or low-side pressure), the shaft moves down. The shaft then pushes the ball off of the seat. This allows more refrigerant flow through the evaporator. A spring at the bottom of the thermostatic expansion valve is not adjustable. Although the thermostatic expansion valve controls the evaporator refrigerant flow, the PCM controls compressor cycling which manages the air conditioning capacity control. This prevents ice build-up.
Expansion (Orifice) Tube Description
The plastic expansion (orifice) tube is located between the following areas:
^ Condenser outlet
^ The evaporator inlet
The plastic expansion (orifice) tube has a mesh screen (3) and orifice. The plastic expansion (orifice) tube provides a restriction to the high-pressure liquid refrigerant in the liquid line. In this way, the plastic expansion (orifice) tube meters the flow of refrigerant to the evaporator as a low-pressure liquid. The expansion (orifice) tube and orifice are protected from contamination by filter screens on both the inlet and outlet sides. When system diagnostics indicate a restricted expansion (orifice) tube, you may need to replace the plastic expansion (orifice) tube. If you find any of the following items on the screen remove them with compressed air:
^ Metal chips
^ Flakes
^ Slivers
Reuse the expansion (orifice) tube if the following conditions exist:
^ The plastic frame is not broken.
^ The brass expansion (orifice) tube is not damaged or plugged.
^ The screen material is not torn.
^ The screen is not plugged with a fine gritty material.
Evaporator Description
The evaporator cools and dehumidifies air before the air enters the passenger compartment. The following events occur in the evaporator:
1. Low-pressure, low temperature liquid/vapor refrigerant enters the evaporator.
2. The refrigerant flows through the evaporator's tubing.
3. The refrigerant evaporates.
4. The refrigerant exits the evaporator as low-pressure, low temperature, mostly vapor refrigerant.
5. As the refrigerant evaporates, the refrigerant absorbs heat from the air flowing over the evaporator.
As the process of heat loss from the air to the evaporator core is taking place, any moisture (humidity) in the air condenses on the outside surface of the evaporator core and the moisture drains off as water.
Condenser Description
The condenser receives high pressure, high temperature refrigerant vapor from the A/C compressor. The condenser is made up of aluminum tubing and cooling fins which allow rapid heat transfer away from the high-pressure, high temperature refrigerant vapor. The cooling fins cause the high pressure, high temperature refrigerant vapor to condense into a high-pressure, medium temperature liquid.
Accumulator Description
The sealed accumulator is connected to the evaporator outlet pipe. The accumulator stores the refrigerant (vapor and liquid) and the oil from the evaporator. A desiccant at the accumulator bottom dries any moisture in the system. An oil bleed hole at the accumulator outlet pipe end provides the oil return path to the compressor. The accumulator is not serviceable and should only be replaced when leaking due to the following conditions:
^ Perforation
^ A damaged sealing area
^ Damaged fastener threads
^ Outside air has entered the system for extended periods of time
Heater Core Description
The heater core is the main component of the heater system. The heater core is located inside of the heater and evaporator module. Engine coolant is pumped into the heater core from the engine whenever the engine is operating. The heater core fins transfers the heat from the engine coolant to the air passing over the heater core. The heater core has specific inlet and outlet tubes. The placement of the heater hoses should be noted prior to servicing the heater core or the heater hoses.
The temperature control is linked to the temperature valve by a flexible control cable. When you rotate temperature control counterclockwise to the full COLD position, the temperature valve is held snugly against the air entrance to the heater core. The following actions occur:
^ All of the airflow from the evaporator bypasses the heater core.
^ No heat transfer occurs.
When you turn the temperature control away from the full COLD position, the temperature valve begins to direct air to the heater core. This action allows air to flow through the heater core. The farther the temperature control is rotated clockwise, the more the temperature valve directs air through the heater core. The air discharge is warmer when most of the airflow is heated in this manner. The air discharge is warmer because the heated and unheated air flows join and mix together thoroughly beyond the heater core.
When you rotate the temperature lever clockwise to the full HOT position, the temperature valve blocks off the passage that allows air to bypass the heater core. This action causes passage of the airflow through the heater core.
Compressor Description
The A/C compressor is driven by a belt from the engine crankshaft through the compressor clutch pulley. The compressor pulley rotates freely, without turning the compressor shaft, until an electromagnetic clutch coil is energized. When voltage is applied in order to energize the clutch coil, a clutch plate and hub is drawn toward the pulley. The magnetic force locks the clutch plate and pulley together as one unit in order to drive the compressor shaft.
High Pressure Relief Valve Description
The compressor is equipped with a pressure relief valve. The pressure relief valve is placed in the system as a safety factor. Under certain conditions, the refrigerant on the discharge side may exceed the designed operating pressure. The valve is designed to open automatically at approximately 3036 kPa (455-525 psi) in order to prevent system damage. Correct any condition that causes this valve to open. Replace any expelled refrigerant oil. Inspect the air conditioning refrigerant pressure sensor for the proper calibration.
Vacuum Hose Harness Description
Vacuum Logic Table:
Vacuum is supplied to the control head through one input port and sourced to 4 output ports. The ports are referred to according to their corresponding functions within the HVAC module.
These ports in turn interface with a 6 port/6 conductor vacuum harness. It connects the control head to the vacuum source and the HVAC module. The vacuum is switched according to the logic table.