Table of Contents
Advertisement
Units with the factory installed low ambient option are
equipped with a solid-state head pressure control which regu-
lates fan speed. A temperature sensor, mounted on either cir-
cuit 1 (569J***A/B units) or both circuits 1 and 2
(569J***T/U 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. P-R). The control
maintains the appropriate head pressure at low ambient tem-
peratures down to –20°F (–28°C).
Wind baffles are required to prevent wind cross currents from
causing abnormally low condensing temperatures.
IMPORTANT: Wind baffles are field-fabricated; they are
not included with the factory-installed Motormaster control
option.
Use 20-gauge sheet metal to fabricate wind baffles (see Fig. S
and Table A). See Fig. T-V for finished installation.
OPERATION
Fan on/off control in cooling-only units (569J***A/B,
569J***T/U) is provided by an outdoor fan relay (OFR) or two
outdoor fan relays (OFR1 and OFR2) for 569J*28T/U. In cool-
ing 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 tem-
perature and 80°F (27°C) at lower ambient. Additionally, out-
door 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
55°F ± 2.16°F, close 60°F ± 2.16°F (open 12.8°C ± 1.2°C,
close 15.6°C ± 1.2°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.
APPENDIX C — LOW AMBIENT OPTION
56
Troubleshooting
OBSERVATION
Fans won't start.
Cooling — Center outdoor
fans (OFM2, OFM4) off
below approximately 55°F
(16°C) outdoor ambient.
Cooling — Center outdoor
fans (OFM2, OFM4) not on
above approximately 60°F
(12.8°C) outdoor ambient.
Cooling — Slow fan speed
for outer fans (OFM1,
OFM3) at start or during
low outdoor ambient
Cooling — Slow fan speed
for outer fans (OFM1,
OFM3) above 85°F (29°F)
outdoor ambient (should
be full speed)
Cooling — motor current
into speed control is
greater than motor
nameplate FLA
Speed Control Sensor Resistance
TEMPERATURE
°F ±2°F
–22
–4
14
32
50
68
77
86
104
122
140
158
POSSIBLE REMEDY
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)
Normal operation
Check low ambient switch (LAS)
Check low ambient relay (LAR)
Normal operation
Check speed control sensor location
Check speed control sensor resistance
Check fan motor capacitor
Normal operation
Up to 30% higher A at partial speed at
low ambient
RESISTANCE
°C ±1°C
Ohms, nominal
–30
88,350
–20
48,485
–10
27,650
0
16,325
12
9,950
20
6,245
25
5,000
30
4,028
40
2,663
50
1,801
60
1,244
70
876
Advertisement
Table of Contents
