More than meets the eye
Collar dimensions are set by SAE Standards for low-side and high-side service ports. Note the knurled base on the low-side port (left).
Viewed from the bottom: the high flow-rate port (center) is installed as a complete assembly. Note the saddle mount on the M-10 port (left).
by Jacques Gordon
Refrigerant service port fittings perform the function of a simple check valve, but they must meet several different demands that make their design quite complex. First of all, they must conform to SAE Standards that define the fitting diameter, locking collar dimensions and distance from the opening to the tip of the valve stem on both the high- and low-side fittings. The goal is to make sure that only the correct service equipment coupling (R/R/R machines) can be connected to them.
Everything below the valve stem tip is designed primarily to satisfy different needs of the car manufacturer. For instance, on the GM assembly line, it takes less than one minute to evacuate the A/C system to 29.45 inHg, pause for a leak-check, then fill it with refrigerant and oil. Of course the vacuum pumps and filling equipment used on the production line are far more powerful than the equipment in a repair shop, but the design of the service port also influences the speed of the operation. Since port diameter is already set by the SAE specification, the valve core must be designed to provide a high flow rate on large systems that require more refrigerant. Schrader makes a service port fitting that flows particularly fast, but it must be installed on the vehicle as a complete assembly. Normally the metal body of a service port is brazed to the metal refrigerant line and then the valve core and rubber seals are installed after it cools. To install a fully-assembled service port, a female-threaded collar is brazed to the metal refrigerant line first, then the service port is screwed into place and sealed with an O-ring.
A less expensive high-flow port uses a ‘saddle’ mount to locate the body on the metal refrigerant line. After it’s brazed into place, the body is used as a pilot to locate the hole that is drilled into the line, and finally the valve core is installed. On a standard service port, the body has a knurled collar at the base that fits directly into a hole in the metal refrigerant line, and the valve core is installed after brazing.
To make it easier to design a quick-disconnect fitting, the threads for the cap are inside the service port body. This also minimizes the possibility of damage that would prevent the cap from screwing on tight enough to make a positive seal. The cap really isn’t designed to hold system pressure, but it must protect the valve from contamination. Tighter regulations on system leakage make the service port cap a more critical part than ever.
Our thanks to Schrader International for contributing parts and information for this article.
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When having your mobile A/C system professionally serviced, insist on proper repair procedures and quality replacement parts. Insist on recovery and recycling so that refrigerant can be reused and not released into the atmosphere.
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