148 Auto Heating and Air Conditioning Copyright by Goodheart-Willcox Co., Inc. to those on the engine radiator. Th e majority of condensers have high pressure compression fi ttings using an O-ring. A few condensers use spring lock fi ttings. Th e sides of the condenser are usually equipped with seals to keep air from bypassing the condenser. One or more electric fans or an engine-driven fan ensures airfl ow at low speeds. Accumulators Accumulators are always located between the evapo- rator and the compressor inlet, Figure 9-9. Accumulators store vaporized refrigerant from the evaporator. Th e accu- mulator absorbs some of the pressure and fl ow fl uctuations that occur as the compressor cycles on and off . It also holds enough extra refrigerant to allow for slight variations in the system charge. Th e accumulator is a large container, usually made of aluminum. If underhood space permits, the accumulator is located close to the evaporator outlet. Note: Some vehicles with two evaporators will have more than one inlet to the accumulator. Operation is the same as with an accumulator with one inlet. Accumulator Operation During cool weather operation, or on startup, some liquid refrigerant may exit the evaporator. To keep liquid refrigerant from getting to the compressor where it could cause damage, the accumulator separates liquid and vapor- ized refrigerant. Th e inlet pipe opens directly into the large chamber of the accumulator. Th e refrigerant slows down as it enters the chamber. When the refrigerant slows down, any liquid refrigerant or oil will go to the bottom of the accumulator. Dirt or debris will also go to the bottom of the accumulator. An internal pipe is connected to the accumulator outlet. Th is internal pipe runs to the top of the accumulator. Since the liquid is at the bottom, only vapor can enter the pipe. Th e pipe is made in a loop that takes it almost to the bottom of the accumulator. At the lowest point of the pipe, a small oil return hole is open to the bottom of the accumulator. Th is hole allows any refrigeration oil at the bottom of the accumulator to be returned to the compressor. Th e hole is small enough so the compressor does not receive too much liquid oil or refriger- ant. A screen surrounds the oil return hole. Th e screen keeps any system debris from clogging the hole or entering the compressor. See Figure 9-10. On many vehicles, a pressure switch is installed on the accumulator. See Figure 9-11. Th is switch may be used to operate the cycling clutch or may send a signal to an on- board computer. Receiver-Driers Th e receiver-drier is a tank that stores condensed refrigerant and a small amount of vaporized refrigerant. Th e receiver-drier is always located at the condenser out- let. Connections are made using compression fi ttings and O-rings. Receiver-driers are manufactured in many sizes and shapes. However, they all perform the same function. Th e main purposes of the receiver-drier are to store refrigerant to make up for slight losses and to remove dirt and moisture. Th e pickup tube leading to the expan- sion valve is at the bottom of the receiver-drier. Since any Figure 9-9. The accumulator is always placed between the evaporator and the compressor inlet. Figure 9-10. The accumulator screen catches debris that would clog the oil return hole. The screen and oil return hole are always placed at the bottom of the internal separator tube.