Lennox MS8 SERIES Installation And Service Procedures page 84

8. COMPONENT: ELECTRONIC EXPANSION VALVE
DESCRIPTION:
Electronic expansion valve is used in Inverter air
conditioning system
automatically. Thus the air conditioner can always stay at
the optimized working conditions with quick cooling, precise
temperature control, low energy consumption, etc. This
valve is reversible and can control the flow under either
cooling or heating condition.
Electronic Expansion Valve (EXV) is mainly composed of
valve body and 12 VDC, rectangular wave coil. The
controller in the air conditioning system can control the step
motor of EXV to synchronize the turning of gear train which
converts the rotation of gears to a pull/push force and moves
the valve pin axially which can change the flow area and flow
of refrigerant accordingly.
The outdoor control sends pulse signal to the coil which
controls the rotor synchronizing the turning of feed screw
and nut, converting the rotation to movement of valve pin.
Thus the flow area and flow of refrigerant will be changed
accordingly.
The EXV is driven by permanent-magnet (PM) type step
motor (claw pole field motor) which consists of two relative
separate parts: 1) step motor coil; 2) multi-pole rotor valve
body. The coil is fixed onto the body through a clipper.
TROUBLESHOOTING:
Check opening and closing operation of valve. Check
operation of valve by measuring temperature differences
between the inlet and outlet pipes of the EXV.
MS8C / MS8H (208-230V)
to adjust flow of refrigerant
Check resistance between blue-
black, blue-yellow, blue-red and
blue-orange. All resistance read­
ings should be within +5 of each
other.
Page 84