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Unit Start Up
Low Ambient Dampers
Operation
Low Ambient Dampers are available as a factory installed option on 20 - 75 Ton units or can be field-
installed. Dampers are used to extend the operation of these units from the standard operational
temperatures to a minimum of 0° F without hot gas bypass or 10° F with hot gas bypass. (These
values apply when wind speed across the condenser coil is less than 5 m.p.h. If typical wind speeds
are higher than 5 m.p.h., a wind screen around the unit may be required.) By restricting the airflow
across the condenser coils, saturated condensing temperatures can be maintained as the ambient
temperatures change.
The low ambient modulating output(s) on the compressor module controls the low ambient
damper actuator for each refrigerant circuit in response to saturated condensing temperature.
When the head pressure control has staged up to fan stage 2 or 3, the modulating output (0 to 10
VDC) will be at 100% (10 VDC). When the head pressure control is at fan stage 1, the modulating
output will control the saturated condensing temperature to within the programmable
"condensing temperature low ambient control point" .
The following Table gives the minimum starting temperatures for both "Standard" & "Low"
Ambient units. Do not start the unit in the cooling mode if the ambient temperature is below the
recommended operating temperatures.
Table 51. Minimum starting temperatures for air-cooled units
(a) Minimum starting temperatures for Evaporative Condenser units is 40
(b) Min. starting ambients in
(c) With or Without HGBP
Damper Installation
When a unit is ordered with the low ambient option (i.e., Digit 19 is a "1" in the model number),
a damper is factory installed over the condenser fans 2B1 & 2B4 (depending on unit size). Refer to
the illustration in
For field installation, mount the dampers over the condenser fans at the locations shown in
Figure 48
with each kit.)
Damper Adjustment (Factory or Field Installed)
The UCM has a factory default setpoint of 90°F . This setpoint can be adjusted using the Human
Interface programming procedures.
Inspect the damper blades for proper alignment and operation. Dampers should be in the closed
position during the "Off" cycle. If adjustment is required;
1. Never depress the actuator clutch while the actuator is energized.
2. At the Human Interface, program the actuator for 0% on circuit #1 and/or circuit #2. (The output
3. Loosen the actuator clamp.
154
Minimum Starting Ambient
(c)
Unit Size
Standard
20 & 40
55°
25 & 30
50°
50, 55
35°
60
30°
70-130
45°
a sump heater and 10
°
F with a sump heater.
°
F and is based on unit operating at min. step of
unloading & 5 mph wind across condenser.
Figure 48
for the damper locations.
and connect the actuator for each circuit. (Refer to the Installation Instructions provided
signal will go to 0.0 VDC.)
(b)
Low Ambient
with HGBP
without HGBP
10°
0°
10°
0°
10°
0°
10°
0°
10°
0°
°
F without
(a)
RT-SVX36G-EN
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