The following are the major components of the air conditioning refrigerant system:
The basic operation of the variable displacement orifice tube (VDOT) refrigeration system is the same as for conventional A/C systems. The VDOT refrigeration system utilizes a variable displacement compressor which contains seven cylinders; a V7 compressor that can maintain the automotive air conditioning demand under all conditions without cycling the compressor.
The basic compressor mechanism is a variable angle wobble-plate with axially oriented cylinders. The control of the compressor displacement is a bellows actuated control valve located in the rear head of the compressor which senses suction pressure. The wobble-plate angle and compressor displacement are controlled by the crankcase-suction pressure differential. When the A/C capacity demand is high, the suction pressure will be above the control point; the control valve will maintain a bleed from the crankcase to suction; no crankcase-suction pressure differential; and the compressor will have maximum displacement. When the A/C capacity demand is lower and the suction pressure reaches the control point, the control valve will bleed discharge gas into the crankcase and close off a passage from the crankcase to the suction plenum. The angle of the wobble-plate is controlled by a force balance on the seven pistons. A slight elevation of the crankcase-suction pressure differential creates a total force on the pistons resulting in a movement about the wobble-plate pivot pin that reduces the plate angle.
The compressor has a unique lubrication system. The crankcase-suction bleed is routed through the rotating wobble-plate for lubrication of the wobble-plate bearing. The rotation acts as an oil separator, which removes some of the oil from the crankcase-suction bleed, rerouting it to the crankcase where it can lubricate the compressor mechanism.
The compressor, depending upon engine usage, is cut-off under certain conditions, such as wide-open throttle, low idle speed, low ambient air temperature, high power steering loads and high engine oil or engine coolant temperatures. The V7 compressor has a mechanical destroker that will destroke during engine speeds of 3000-3800 RPM.
When the air conditioning system is turned OFF, the refrigerant in the system will flow from the high pressure side of the evaporator tube orifice to the low pressure side until the pressure is equalized. When the engine is turned to OFF without first turning OFF the A/C system, this may be detected as a sound of liquid flowing (a hissing sound) for 30-60 seconds and is a normal condition.
The accumulator is downstream of the evaporator core. Refrigerant vapor and refrigerant oil are received by the accumulator from the evaporator. The accumulator separates moisture from refrigerant vapor -- a desiccant located inside the bottom of the accumulator is used to dry the refrigerant -- and stores the air conditioning refrigerant as both a vapor and a liquid, along with refrigerant oil. An internal oil bleed hole at the outlet of the accumulator internal tube provides the oil return path to the compressor. The accumulator is sealed and non-serviceable. Replace the accumulator only when leaking due to any of the following conditions:
The air conditioning 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 to energize the clutch coil, the clutch plate and hub is drawn rearward toward the pulley. The magnetic force locks the clutch plate and pulley together as one unit in order to drive the compressor shaft.
The condenser is located in front of the radiator. The condenser is made up of coils, which carry the refrigerant and cooling fins used to provide rapid transfer of heat. The air passing through the condenser cools the high pressure refrigerant vapor, causing it to condense into a high pressure liquid.
Engine cooling fan operation is crucial to the proper operation of the air conditioning system. The cooling fans ensure the proper amount of air flow across the condenser throughout the vehicle operating range.
Fan operation should be checked during any air conditioning diagnosis procedure. Special attention should be given to the fan whenever excessive high side pressures are encountered.
The plastic expansion (orifice) tube, with its mesh screen and orifice is located in the forward end of the evaporator tube -- rear. The expansion (orifice) tube provides a restriction to the high pressure liquid refrigerant in the liquid line, metering the flow of refrigerant to the evaporator as a low pressure liquid. The expansion tube orifice is protected from contamination by filter screens on both the inlet and outlet sides.
The evaporator core is used to cool and dehumidify the air before the air enters the passenger compartment.
High pressure liquid refrigerant flows through the expansion (orifice) tube and becomes low pressure refrigerant liquid before entering the evaporator. The heat in the air passing through the evaporator core is lost to the cooler surface of the core, thereby cooling the air. As a process of heat loss from the air to the evaporator core surface is taking place, any moisture (humidity) in the air condenses on the outside of the evaporator core and is drained off as water. As the air passes through the core, the cooler surfaces absorb the heat, cooling the air. As the air is being cooled, any humidity in the air condenses on the outside of the evaporator core and is drained off as water.
