40
APPENDIX C
Low Ambient Option — Factory Installed
Units with the factory installed low ambient option are
equipped with a Motormaster
R
solid--state head pressure
control which regulates fan speed. A temperature sensor,
mounted on circuit 1 of the outdoor coil (see Figs. 32 and
33) 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 --28
_
C (--20
_
F).
Wind baffles are required to prevent wind cross currents
from causing abnormally low condensing temperatures.
S
Use 20--gauge sheet metal to fabricate wind baffles (see
Fig. 34 and Table 13) and mounting brackets (see Fig.
35).
NOTE
: Mounting brackets are for use on the size 16
units only.
S
Install the wind baffles as show in Fig. 36, for the size
16 units and Fig. 37, for the size 25 units .
Operation —
Fan on/off control in cooling--only units 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 38
_
C (100
_
F)
at higher outdoor ambient temperature and 27
_
C (80
_
F) 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 5.5
_
C
+/-- 2.8
_
C, close 13.9
_
C +/-- 2.8
_
C (open 42
_
F +/-- 5
_
F,
close 57
_
F +/-- 5
_
F ).
To override the speed control for full fan speed operation
during service or maintenance, either:
a. remove sensor and place in hot water >49
_
C
(>120
_
F), or
b. rewire to bypass control by connecting speed
control input and output power wires.
Troubleshooting —
OBSERVATION
POSSIBLE REMEDY
Fans won’t start
All fans:
Check power & 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
16
_
C (60
_
F) outdoor am-
bient.
Normal operation
Cooling --- Center outdoor
fans (OFM2, OFM4) not on
above approximately 16
_
C
(60
_
F) 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 29
_
F (85
_
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 name-
plate FLA
Normal operation
Up to 30% higher A at partial speed
at low ambient
Speed Control Sensor Resistance —
TEMPERATURE
TEMPERATURE
RESISTANCE
_
C +/---1
_
C
_
F +/---2
_
F
Ohms, nominal
---30
---22
88350
---20
---4
48485
---10
14
27650
0
32
16325
10
50
9950
20
68
6245
25
77
5000
30
86
4028
40
104
2663
50
122
1801
60
140
1244
70
158
876
38A
U
D
Summary of Contents for 38AUD 16 Series
Page 21: ...21 CIRCUIT 1 CIRCUIT 2 C10946 Fig 16 38AUD 16 Charging Chart Novation 38AUD...
Page 22: ...22 C10949 Fig 17 38AUD 16 Charging Chart RTPF 38AUD...
Page 23: ...23 CIRCUIT 1 CIRCUIT 2 C10950 Fig 18 38AUD 25 Charging Chart RTPF 38AUD...
Page 24: ...24 C10084A Fig 19 Typical 38AUD 16 Wiring Diagram 38AUD...
Page 25: ...25 C10085A Fig 20 Typical 38AUD 25 Wiring Diagram 38AUD...