Carrier 50LC 07, Инструкции по обслуживанию и техническому обслуживанию, Страница: 86 / 100

86
Low Ambient Cooling Operation down to 40
_
F (4
_
C)
In Low Ambient RTU conditions when the temperature is between 55
_
F (13
_
C) and 40
_
F (4
_
C), the Low Ambient Switch
(LAS) will be active and the outdoor-fans will run to the pre-set factory outdoor-fan speed. When the temperature is
greater than 65
_
F (18
_
C), the Low Ambient Switch will deactivate and the outdoor-fans will run in the standard cooling
mode. If the Outdoor Fan Select Switch (see Fig. 71) is in the up position, the outdoor fans will run in the Fan Cycle
Speed Mode (FCS) set to 250 rpm. If the Outdoor Fan Select Switch is in the down position, the outdoor fans will run in
the Minimum Fan Speed Mode (MIN) set to 160 rpm regardless of the cooling demand.
OF SPEED
SELECT
UP
FCS
MIN
DOWN
C13327
Fig. 71 -- Outdoor Fan Speed Select Switch
LC size 007 units have a SPST normally open Low Ambient Switch wired across the TS and OF terminal and a jumper
placed across the PS terminal (See Fig. 72). When the LAS is active, the switch will close making contact to the OF
terminal. This is done for units that require all outdoor fans to run at the same pre-set factory Low Ambient Speed.
LC Size 008 through 012 Units have a SPDT Low Ambient Switch wired to the OF terminal and the Outdoor Fan Relay
(See Fig. 73). The jumper across the PS terminal will be removed. When the LAS is active, the switch will close making
contact to the OF terminal and will drop connection to the ODF Relay. When electrical connection is removed from the
ODF Relay, the PS connection will be opened. This will place the third outdoor-fan electrically isolated from receiving
any speed command, which will then turn the motor off. This is done for units that only require two outdoor fans to run
at the same pre-set factory Low Ambient Speed.
JUMPER ON
LAS
SPST
PS PS
TS OF
C13328
Fig. 72 -- Schematic of SPST Low Ambient Switch
LAS
SPST
PS PS OF
REMOVE JUMPER
ODF RELAY
24VAC
TB-4
C13329
Fig. 73 -- Schematic SPDT Low Ambient Switch
The Low Ambient Outdoor Fan Control chart (listed below) shows the operation of the outdoor fans for each unit
Low Ambient Temperature Outdoor Fan Control
LC
Size
No. of Fans On No. of Fans Off Switch
LAS
FIG. No.
OF Select Switch RPM
007 2 0 (1) SPST 72 Up 250
008 2 1 (1) SPDT 73 Down 160
009 2 1 (1) SPDT 73 Down 160
012 2 1 (1) SPDT 73 Down 160
Heating
In the Heating Mode (W1 on the thermostat), power is applied to the G and W1 terminal at the ISC board and energizes the
first state of electric heat. Upon more call for heat (W2 at the thermostat), power is applied to the G and W2 terminal at
the ISC board and energizes the second state of electric heat. The VFD controlled indoor fan will operate at high speed
regardless of the heating demand.