50
APPENDIX C — LOW AMBIENT OPTION
Units with the factory installed low ambient option are
equipped with a Motormaster
®
solid-state head pressure con-
trol which regulates fan speed. A temperature sensor, mounted
on either circuit 1 (569J***A/B/G/H units) or circuit 2
(569J***D/E/F units) of the outdoor coil controls the speed of
approved outdoor fan motors in order to maintain a constant
head pressure in the outdoor coil (see Fig. L and Fig. M). The
control maintains the appropriate head pressure at low ambient
temperatures down to –20°F (–28°C).
Wind baffles are required to prevent wind cross currents from
causing abnormally low condensing temperatures.
Use 20-gauge sheet metal to fabricate wind baffles (see Fig. N
and Table A).
OPERATION
Fan on/off control in cooling-only units (569J***A/B/G/H,
569J***D/E/F) is provided by an outdoor fan relay (OFR). In
cooling mode, fan motor speed of outdoor motors OFM1 and
OFM3 is regulated by the speed control temperature sensor on
outdoor coil 1 for a minimum coil condensing temperature of
approximately 100°F (38°C) at higher outdoor ambient tempera-
ture and 80°F (27°C) at lower ambient. Additionally, outdoor fan
motor OFM2 and OFM4 are turned on/off by the low ambient
temperature switch (LAS), operating the low ambient relay
(LAR). The LAS control temperatures are open 42°F
5°F,
close 57°F
5°F (open 5.5°C 2.8°C, close 13.9°C 2.8°C).
To override the speed control for full fan speed operation
during service or maintenance, either:
a. remove sensor and place in hot water >120°F (>49°C).
or
b. rewire to bypass control by connecting speed control
input and output power wires.
Troubleshooting
Speed Control Sensor Resistance
IMPORTANT: Wind baffles are field-fabricated; they are not
included with the factory-installed Motormaster control
option.
OBSERVATION POSSIBLE REMEDY
Fans won’t start.
All fans:
Check power and wiring
Check outdoor fan relay (OFR)
OFM1, OFM3 only:
Check speed control sensor location
Check speed sensor resistance
OFM2, OFM4 only:
Check low ambient switch (LAS)
Check low ambient relay (LAR)
Cooling — Center outdoor
fans (OFM2, OFM4) off
below approximately 60°F
(16°C) outdoor ambient.
Normal operation
Cooling — Center outdoor
fans (OFM2, OFM4) not on
above approximately 60°F
(16°C) outdoor ambient.
Check low ambient switch (LAS)
Check low ambient relay (LAR)
Cooling — Slow fan speed
for outer fans (OFM1,
OFM3) at start or during low
outdoor ambient
Normal operation
Cooling — Slow fan speed
for outer fans (OFM1,
OFM3) above 85°F (29°F)
outdoor ambient (should be
full speed)
Check speed control sensor location
Check speed control sensor resistance
Check fan motor capacitor
Cooling — motor current into
speed control is greater than
motor nameplate FLA
Normal operation
Up to 30% higher A at partial speed at
low ambient
TEMPERATURE RESISTANCE
°F ± –2°F °C ± –1°C Ohms, nominal
–22 –30 88,350
–4 –20 48,485
14 –10 27,650
32 0 16,325
50 12 9,950
68 20 6,245
77 25 5,000
86 30 4,028
104 40 2,663
122 50 1,801
140 60 1,244
158 70 876
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