49
APPENDIX C

Low Ambient Option — Factory Installed

Units with the factory installed low ambient option are
equipped with a MotormasterRsolid--state head pressure
control which regulates fan speed. A temperaturesensor,
mounted on circuit 1 of the outdoor coil (see Figs. 44
through 47) controls the speed of approved outdoor fan
motors in order to maintain a constant head pressure in the
outdoor coil. 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. 48 and Table 15).
Operation—
Fan on/off control in cooling--onlyunits (569J) i s 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 temperature 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
duringservice 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 —
OBSERVATION POSSIBLE REMEDY
Fanswon’t start Allfans:
Checkpower & wiring
Checkoutdoor f an relay (OFR)
OFM1,OFM3 only:
Check speed control sensor location
Check speed sensor resistance
OFM2,OFM4 only:
Checklow ambient switch (LAS)
Checklow ambient relay (LAR)
Cooling ---Center outdoor
fans(OFM2, OFM4) off
belowapproximately 60_F
(16_C)outd oor ambient.
Normaloperation
Cooling ---C enter outdoor
fans (OFM2, OFM4) not on
above approximately 60_F
(16_C) outdoor ambient
Checklow ambient switch (LAS)
Checklow ambient relay (LAR)
Cooling ---Slow fan speed
forouter fans (OFM1,
OFM3)at start or during
lowoutdoor ambient
Normaloperation
Cooling ---Slow fan speed
forouter fans (OFM1,
OFM3)above 85_F(29_F)
outdooramb ient (should
befull speed)
Check speed control sensor location
Check speed control sensor
resistance
Checkfan motorcapacitor
Cooling ---motor current
intospeed control is
greaterth an motor name-
plateFLA
Normaloperation
Upto 30% higher Aat partial speed
atlow ambient
SpeedControl Sensor Resistance —
TEMPERATURE RESISTANCE
_F + / ---2_F__C +/--- 1C Ohms,nominal
---2 2 ---3 0 88350
---4 --- 2 0 48485
14 ---1 0 27650
32 016325
50 10 9950
68 20 6245
77 25 5000
86 30 4028
104 40 2663
122 50 1801
140 60 1244
158 70 876
569J