The above from Sporlan 10-11.On suction lines 7/8 OD and larger, the
surface temperature may vary slightly
around the circumference of the line. On
these lines, it is generally recommended that
the bulb be installed at 4 or 8 oclock on the
side of the horizontal line, and parallel with
respect to the direction of flow. On smaller
lines the bulb may be mounted at any point
around the circumference, however locating
the bulb on the bottom of the line is not
recommended as an oil-refrigerant mixture
is generally present at that point.
Field experience says that the 'clock' position doesn't matter a whole lot. A good insulation wrap means more than quibbling over 2 o'clock vs 3 o'clock and gets you to beer o'clock a whole lot faster.