Toshiba HFC R407C, Service Manual

Page: 63 / 80

63
Control features
Outdoor unit
No. Control Description Diagram
1 Defrost • During heating operation, defrost is
(Heating mode) controlled by the outdoor unit heat
exchanger temperature sensor (TE).
• When the cumulative operating time with
TE in zone [A] has amounted to 25 minutes,
defrost operation starts. Subsequent
defrosts occur after a cumulative time of 55
minutes. When heating operation resumes
after defrost, the timer is reset.
• The maximum defrost period after TE
returns to zone [B] is 1 minute.
• Heating operation resumes immediately
after TE returns to zone [C].
2 Oil retrieval • During cooling operation, oil retrieval is
(Cooling mode) performed if one or more Indoor units are
OFF.
• If this condition is satisfied, when cooling
operation commences, oil retrieval takes
place for 1 minute.
If cooling operation continues, oil retrieval is
repeated for 1 minute every 60 minutes.
• During oil retrieval the following occurs:
a. All Multi Controller PMVs are opened.
The degree of opening is dependant
on the capacity of the Indoor unit .
b. If the D.O.L. compressor is OFF the
inverter compressor speed increases
to SD.
• When cooling operation ends the timer is
reset.
3 Superheat control • Superheat is controlled by the Multi
(Cooling mode) Controller for cooling operation.
The level of superheat is determined by the
difference between the evaporator outlet
temperature for each indoor unit (ThA, B,
C, D) and the saturation temperature (ThX).
• If the superheat of an indoor unit enters
zone [Y], the relevant M/C PMV opens
further to compensate for this increase. The
degree of additional opening is dependant
on the capacity of the indoor unit.
• When zone [Z] is reached the PMV opening
is held at the level set in zone [Y].
• When the level of superheat returns to zone
[X] the control is cancelled.
Temp.
(°C)
Superheat
(°C)
12
8
-3
A
C
B
Cooling mode
Oil
retrieval
Oil
retrieval
Compr.
off
Timer
reset
1 min.
1 min.
60 min.
< 60 min.
13
9
Y
Z
X