Trane R Series Diagnostic Troubleshooting Repair page 59

Module Power and Miscellaneous I/O
A "FLAG" stop is located at either end of the threaded portion of the motor
shaft. The stops interfere with the milled flag on the drive coupling, restricting
rotation of the motor shaft and producing a clicking sound when the valve is
driven fully OPEN or CLOSED.
Figure 14 SEO 70, 100 Electronic Expansion Valve Cut Away View
SEHI-100 Valve
The valve is a stepper-motor type, direct acting valve. It uses a two-phase
motor, with each phase having 75 ohms of resistance.
The supply voltage (12 VDC) is switched on and off to each phase, to step the
valve open or closed. Each step is 0.00007" of stroke, with a full stroke of
6376 steps.
The step motor used in the SEHI valve is a permanent magnet rotor type.
Each step creates a 3.6° rotation of the rotor. This rotation is increased in
torque and reduced in speed by a 12.25:1 gear train. Final rotation is
converted to linear motion by the use of a lead screw and threaded drive
coupling. Forward motion of the motor extends the drive coupling and pin,
which moves the valve to the closed position. Backward rotation of the motor
retracts the drive coupling and pin modulating the valve in the opening
direction. Full forward or backward travel, while the valve is assembled, is
limited by the valve seat in the closed position or an upper stop in the open
direction. A slight clicking sound may be heard at either of these two
positions and does no harm to the valve or drive mechanism.
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