Low Ambient Fan Cycling - Lennox Prodigy M2 Application Manual

5. Low Ambient Fan Control
5.1. High Efficiency A Box Fan Operation
The outdoor fan in a high efficiency A Box unit operates at three distinct speeds; High, Low and Extra−low. At higher outdoor
temperatures, (above 65F), the fan operates at high speed for a high cooling demand and at low speed for a low cooling or
de−humidification demand. At low outdoor temperatures the fan is off until the liquid pressure switch, S11 closes. Then the
fan runs at extra−low speed.
5.2. Low Ambient Fan Cycling − Other Units
During low ambient conditions, various outdoor fans are cycled by liquid line pressure switches; S11, S84, S85 and S94. The
M2 unit controller will also de−energize fans due to low outdoor temperature. See Figure 4, for fan layouts and tables 9
through 14 for low ambient fan operations.
BOX
Size
A
BOX BOX
B
BOX
C1
BOX
C2
BOX
C3 C3
BOX
E
BOX
Fan Layout
Figure 4. Number of Compressors/Fans and Fan Layout
Models
LCH, LGH 36H,48H,60H
LCH, LGH 36S,48S,60S,72H
LCH, LGH 090,102,120,150
LCH, LGH 156
LCH, LGH 180
LCH, LGH 210
LCH, LGH 240/300S
LCH, LGH 420,480,540,600
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5. Low Ambient Fan Control
Compr. Fans
1 (vari-
1 (2 step)
able)
1
2
3 (2 out-
3
puts)
3
3
4
4
PRODIGYT M2 UNIT CONTROLLER
1
2
4
6
6
6