Rebuilt GM R-4 compressors are not recommended. However, it would be a better choice than its bigger brother, the A-6. The R-4 is larger in capacity than we like in an average classic car installation. It has basically the same characteristics as the A-6 compressor, except it seems to fit in smaller spaces and is much lighter due to its mostly aluminum construction. It has just under 10 cubic inches of displacement per revolution, with four cylinders radiating from its crankshaft. The GM/Frigidaire R-4 is the short (7 1/2-inch) and fat (7-inch dia.) compressor found on later GM vehicles. Using the GM/A-6 compressor has been a painful and costly experience for many restorers and rodders. We mention this compressor only lightly because the only place we would recommend using it would be in a high-value pure restoration project or in an extremely large vehicle with a high-capacity evaporator, or even two evaporators. It is about 12.5 inches long and 5 inches in diameter, with over 12 cubic inches of displacement per revolution. It has the same characteristics, except that it is very large, both in capacity and external dimensions. The GM/Frigidaire A-6 (long type) compressor shares the same basic design as the Sanden, with one additional cylinder. The York also has higher torque requirements for peak pumping, and they don’t like higher RPM operating speeds. The reciprocating motion causes it to vibrate more than modern Sanden compressors. The York compressor is much like a lawn mower engine, being a two cylinder, reciprocating pump. The York is a rarity these days, but can be identified by its large square shape. The York compressor was OEM equipment on most American cars in the fifties, sixties, and early seventies. The numbering system is interpreted as follows: SD 508 = 5 cylinder/8.4 cubic inch, SD 7 = 7 cylinder/ 6.1 cubic inch. These characteristics make the Sanden an almost ideal performance compressor.ĭisplacement sizes for Sanden units are identified by the numbers on the label on the case. It can be operated at continuous crank speeds of 6000 RPM. Above 1200 RPM, efficiency rapidly increases at operating speeds of 1800 to 2400 RPM it is about the most efficient pump on the market. On the average classic car requiring a smaller sized condenser, that is a blessing. This puts less heat load on the condenser and consequently on the radiator at idle speeds. The Sanden compressor has another characteristic which we like, especially for street rods: its short stroke, low-displacement-per-cylinder configuration tends to make it less efficient at low RPM ranges (1200 and below), the same speed at which our engine-driven radiator fans are least efficient. The Sandens are so popular because they operate smoothly, with a minimum amount of torque required to operate, because the load is distributed over multiple short-stroke cylinders. Even though it is commonly refered to as a rotary, it is not. It has five or seven cylinders running lengthwise, thus the name axial compressor. It is easy to spot with its barrel shape, aluminum color and small overall size. The Sanden compressor is a compact cylindrical unit about 8-1/2 inches long and about 5 inches in diameter. And yes, a very few York/Tecumsehs are still on some restored classics. We do see a few engine swaps that retain the original General Motors/Frigidaire (DAG and R4), or the Ford Nippondenso compressors. The type of compressor most commonly used now in aftermarket systems is the axial type by Sanden (See our line of SANDEN COMPRESSORS). The next most critical part of an air conditioning system in terms of providing optimum performance and trouble-free service is matching the compressor to the other system components. Basic Auto Air Conditioning Compressor Facts
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