658 Modern Refrigeration and Air Conditioning Copyright Goodheart-Willcox Co., Inc. Process Tube and Adapters Many manufacturers install a small length of tubing through a compressor’s housing so they can evacuate, test, and charge the appliance’s refrigeration system during the assembly process. Such a tube is known as a process tube. When the assembly process is complete, the process tube is sealed up, but left in the system so it can be used by a service technician. Access to a hermetic system is possible by first installing a piercing valve to a process tube, brazing on an extension and fitting, or by installing an adapter on the tube. Gauges and other service equipment can then be attached to the process tube. Review Chapter 10, Equipment and Instruments for Refrigerant Handling and Service, for more information about piercing valves. A process tube adapter allows a technician to use the process tube without soldering or brazing on an extension or flaring the tubing. It is installed by cutting off the sealed end of the process tube, sliding the pro- cess tube adapter over the process tube, and tightening it. A gauge hose can then be attached to the fitting at the end of the adapter. The adapter provides a positive seal. See Figure 25-21. When service is completed, a pinch-off tool is used to seal off the process tube just behind the adapter, the adapter is removed, and the end of the process tube is then brazed shut. Pro Tip Installing a Schrader Valve When the refrigerant has been recovered from a system, it is always a good practice to install a Schrader valve fitting in the system if it does not already have one. Installing a permanent fitting will make future service work safer and Safety Note Phosgene Gass When brazing a pinched-off process tube on a charged system, make sure that the high-side and low--l side pressures are equalized and that you are working a well-ventilated area. If there is a leak from an improper pinch off, heating leaking refrigerant could create harm-- ful phosgene gas..g Pinch-Off Tool A pinch-off tool can apply a great deal of pressure to a small area of soft copper tubing (up to 3/8″ OD) to seal it off. This tool can be used to isolate parts or sections of tubing when an emergency such as a bad leak arises. Lines should be pinched only when absolutely necessary. There are several different types of pinch-off tools. Two common types are shown in Figure 25-22. Installin g a Schrader Valv e When the refrigerant has been recovered f rom a system, it is always a good practice to install a Schrader valve fittin g in the system if it does not already have one. Installing a permanent fitting will make future service work safer and easeasier..rei Phosgene Ga When brazin g a pinched-off process tube on a charged system, ma ke sure that t h e high-side an d ow side pressures are equalized an d that you are working iin n a well-ventilated area. If there is a leak from an improper pinch off, heatin g leakin g refrigerant could create harm ful phosgene as Another type of pinch-off tool has a screw shaft with a ball bearing on the end that presses against the tube. The tool is placed over the copper tubing in the same manner as a tubing cutter. The tubing is slowly compressed by turning the pinch-off tool handle clock- wise. See Figure 25-23. As the handle is turned, the ball bearing presses into the tubing and compresses it against the die on the bottom of the tool. A permanently pinched line is produced. Care must be taken to avoid over tightening the pinch-off tool. The tool should be left in place until the tubing end is sealed by brazing, Figure 25-24. Process tube Flanges Clamp and seal Service connection Ritchie Engineering Co., Inc. – YELLOW JACKET Products Division Figure 25-22. Two styles of pinch-off tools. A—This type of pinch-off tool resembles and operates like locking pliers. B— On this type of pinch-off tool, the wing nuts are loosened. The tubing is inserted through the rectangular jaws in the center of the tool. The wing nuts are then tightened to deform and seal the tubing. Goodheart-Willcox Publisher Figure 25-21. Cutaway of a process tube adapter installed on a process tube. As the two flanges are tightened together, the seal is compressed, causing it to expand in the center. This creates a tight seal between the process tube and the flange.