Defrost Control (Only In Heating Operation) - Toshiba RAS-25U2FVG-ND Service Manual

Item
7. Defrost control (This function removes frost adhered to the outdoor
(Only in heating heat exchanger.)
operation)
The temperature sensor of the outdoor heat ex-
changer (Te sensor) judges the frosting status of the
outdoor heat exchanger and the defrost operation is
performed with 4-way valve reverse defrost system.
Start of heating operation
0 ' 10 ' 15 '
0°C
–3°C
–7°C
– 25°C
*
* The minimum value of Te sensor 10 to 15 minutes
after start of operation is stored in memory as Te0.
Table 1
When (TE0 - TE) - (TO0 - TO) ≥ 3°C and SH-SHO ≤ 2
A zone
in A zone, defrost operation starts.
When (TE0 - TE) - (TO0 - TO) ≥ 2°C and SH-SHO ≤ 2
B zone
in B zone, defrost operation starts.
When TE ≤ -25°C and SH-SHO ≤ 2 in C zone,
C zone
defrost operation starts.
More than 70 minutes accumulated heating
D zone
operation time condition TE < 0°C
Operation flow and applicable data, etc.
Operation time
(Minute)
29 ' 35 '
A zone
B zone
C zone
The necessity of defrost operation is
detected by the outdoor heat exchanger
temperature. The conditions to detect the
necessity of defrost operation differ in A,
B, or C zone each. (Table 1)
<Defrost operation>
• Defrost operation in A to C zones
1) Stop operation of the compressor for
20 seconds.
2) Invert (ON) 4-way valve 10 seconds
70'
after stop of the compressor.
3) The outdoor fan stops at the same time
when the compressor stops.
4) When temperature of the indoor heat
exchanger becomes 38°C or lower,
stop the indoor fan.
<Finish of defrost operation>
D zone
• Returning conditions from defrost
operation to heating operation
1) Temperature of outdoor heat exchanger
rises to +8°C or higher.
2)Temperature of outdoor heat exchanger is
kept at +5°C or higher for 80 seconds.
3) Defrost operation continues for
15 minutes.
<Returning from defrost operation>
1) Stop operation of the compressor for
approx. 50 seconds.
2) Invert (OFF) 4-way valve approx. 40
seconds after stop of the compressor.
3) The outdoor fan starts rotating at the
same time when the compressor starts.
- 38 -
Description