Refrigeration System

VDOT Refrigeration System:

Accumulator:

Muffler:

Expansion (Orifice) Tube:

The variable displacement orifice tube (VDOT) is a variable displacement compressor. This compressor can match the air conditioning demands under all conditions without cycling. The basic compressor mechanism is a variable angle wobble-plate with five axially oriented cylinders. The center of control of the compressor displacement is a bellows actuated control valve located in the rear head of the compressor that senses compressor suction pressure. The wobble-plate angle and compressor displacement are controlled by the crankcase-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 valve will maintain a 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 five 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.

Accumulator

Refrigerant leaving the evaporator flows into the accumulator, which acts as a holding tank and separates any remaining liquid refrigerant from the vapor. Refrigerant oil also collects in the accumulator. At the bottom of the accumulator is a packet of desiccant, which absorbs and holds any moisture that may have entered the refrigeration system. This desiccant is specifically designed for R-134a.

Refrigerant exits from the top of the accumulator to insure that no liquid refrigerant enters the compressor. An oil bleed hole in the outlet pipe provides a path for lubricating oil to reach the compressor.

The accumulator is serviced as an assembly by replacement, but should ONLY be replaced when the shell is perforated and a refrigerant leak is found, or if the system has been open for a prolonged period of time (greater than 24 hours).

A/C Compressor (V5)

The A/C compressor is belt driven from the engine crankshaft through the compressor clutch pulley. The compressor pulley rotates without driving the compressor shaft until an electromagnetic clutch coil is energized. When voltage is applied to energize the clutch coil, the clutch plate and hub assembly is drawn toward the pulley. Magnetic force locks the clutch plate and pulley together as one unit to drive the compressor shaft

When the compressor shaft is driven, the compressor pulls low-pressure, low temperature vapor from the accumulator; compresses it into high-pressure, high temperature vapor; and pumps it into the condenser. Carried with the refrigerant is the refrigerant oil which is used to lubricate the compressor.

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 on oil separator, which removes some of the oil from the crankcase where it can lubricate the compressor mechanism.

When the engine is turned off with the A/C system operating, the refrigerant in the system will flow from the high pressure side of the expansion (orifice) tube to the low pressure side until the pressure is equalized. This may be detected as a faint sound of liquid flowing (hissing) for 30 to 60 seconds and is a normal condition.

Unit Repair Information

For bench repair of the air conditioning compressor, refer to compressor repair.

Muffler

A muffler is placed in the compressor high-side (discharge) line to reduce compressor noises and line vibrations. The muffler is an integral part of the suction/discharge refrigerant hose assembly which must be replaced in order to replace the muffler. The muffler should only be replaced if an internal blockage is detected.

Condenser

The condenser assembly, mounted in front of the radiator, 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 and causes it to condense into a high-pressure, medium temperature liquid.

Cooling Fans

The Cooling Fans provide air flow through the condenser and radiator in order to continue heat dissipation during slow or idle vehicle operation.
The fans are controlled by the PCM which turns them on and off as needed depending on coolant temperature and A/C status.

Expansion (Orifice) Tube

The expansion tube restricts the flow of high-pressure, medium temperature liquid refrigerant from the condenser. As the high-pressure, medium temperature liquid refrigerant passes through the expansion tube, it expands to become a low-pressure, low temperature liquid/vapor mixture.

The expansion tube consists of a small brass tube (the orifice) molded into a plastic holder, with fine mesh screening protecting both ends of the tube. The expansion tube is installed inside the evaporator inlet refrigerant line where it connects to the condenser outlet. The expansion tube is serviced as an assembly by replacement only.

When the engine is turned off during A/C system operation, refrigerant in the system flows from the high side of the system to the low side through the expansion tube until pressures equalize. This may be detected as a hissing sound for 30 to 60 seconds after shut down, and is normal.

Evaporator

The evaporator cools and dehumidifies air before it enters the passenger compartment. Low-pressure, low temperature liquid/vapor refrigerant enters the evaporator; flows through its tubing; evaporates; and exits the evaporator as low-pressure, low temperature, mostly vapor refrigerant. As the refrigerant evaporates, it 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 is drained off as water.