Mitsubishi Electric CITY MULTI PUHY-P400YEM-A Service Handbook page 179

Event
The four-way solenoid of the con-
stant rate unit turns on during
cooling system operation.
The constant rate unit does not
operate after turning on the power.
Capacity control unit solenoids
21S4a and 21S4b turn on and off
in turn during defrosting.
The indoor unit LEV closes
completely during defrosting.
The indoor unit LEV closes
completely during operation.
Remote controller display
Normal display
Normal display
Normal display
Normal display
Normal display
-176-
Cause
In order to prevent intrusion of the refrigerant while the
constant rate unit is shut down, the four-way solenoid of
the constant rate unit is on during cooling, off during heat-
ing, and off during shut down.
In cases where preparation for constant rate unit startup is
not complete, the constant rate unit will not operate for a
maximum of 7 hours after turning on the power. (For
example, when the outside temperature is very low or
when the capacity of the indoor unit is very small.)
When defrosting operations are performed using only the
capacity control unit, the solenoids are turned on and off
alternately at fixed intervals.
When defrosting operations are performed using only the
capacity control unit, the indoor unit LEV close completely.
In the event that there is excessive refrigerant flow to the
constant rate unit, the LEV of all indoor units close com-
pletely, and liquid correction operation is performed in
order to prevent excessive refrigerant. (Liquid correction
control)