JOHNSON CONTROLS
140
Form 150.63-NM9
Issue date: 5/20/2021
SECTION 8 – UNIT OPERATION
Figure 40 -
Discharge Air Temperature Control
20 sec.
30 sec.
60 sec.
control range 60 sec.
unloading
unloading
unloading
(no compressor staging) loading
51.5°F
52.5°F
53.0°F
55.0°F
57.0°
(10.8°C)
(11.4°C)
(11.7°C)
(12.8°C)
(13.9°C)
Low Limit Setpoint High limit
Discharge Air Temperature Control – Compressor Staging
Setpoint = 55.0°F (12.8°C) Range = +/- 5°F (-12.2°C)
Table 17 -
Discharge Air Temperature Control for 5 and 6 Compressors (7 and 8 Steps)
LEAD SYSTEM
LAG SYSTEM
*STEP
COMP 1
COMP 2
COMP 3
COMP 1
COMP 2
COMP 3
0
OFF
OFF
OFF
OFF
OFF
OFF
1
ON+HG
OFF
OFF (
See Note 1)
OFF
OFF
OFF
2
ON
OFF
OFF
OFF
OFF
OFF
3
ON
OFF
OFF (
See Note 2)
ON
OFF
OFF
4
ON
ON
OFF (
See Note 3)
OFF
OFF
OFF
5
ON
ON
OFF
ON
OFF
OFF
6
ON
ON
OFF
ON
ON
OFF
7
ON
ON
ON
ON
ON
OFF
8
ON
ON
ON
ON
ON
ON
Notes:
1. Step 1 is Hot Gas Bypass and is skipped when loading occurs. Hot Gas Bypass operation is inhibited during Pumpdown. For Discharge Air
Temperature Control the Hot Gas Bypass solenoid is energized only when the lead compressor is running and the DAT is less than SP, the
Hot Gas Bypass solenoid is turned OFF when the DAT is more than SP + CR/2.
2. Step 3 is skipped when loading occurs.
3. Step 4 is skipped when unloading occurs.
* STEP can be viewed using the OBeforeDATA key and scrolling to COOLING DEMAND.
Table 18 -
Discharge Air Temperature Control for 4 Compressors (6 Steps)
* STEP can be viewed using the OBeforeDATA key and scrolling to COOLING DEMAND.
Notes:
1. Step 1 is Hot Gas Bypass and is skipped when loading occurs. Hot Gas Bypass operation is inhibited during Pumpdown. For Discharge Air
Temperature Control the Hot Gas Bypass solenoid is energized only when the lead compressor is running and the DAT is less than SP, the
Hot Gas Bypass solenoid is turned OFF when the DAT is more than SP + CR/2.
2. Step 3 is skipped when loading occurs.
3. Step 4 is skipped when unloading occurs.
* STEP can be viewed using the OBeforeDATA key and scrolling to COOLING DEMAND.
LEAD SYSTEM
LAG SYSTEM
*STEP
COMP 1
COMP 2
COMP 1
COMP 2
0
OFF
OFF
OFF
OFF
1
ON+HG
OFF (
See Note 1)
OFF
OFF
2
ON
OFF
OFF
OFF
3
ON
OFF (
See Note 2)
ON
OFF
4
ON
ON (
See Note 3)
OFF
OFF
5
ON
ON
ON
OFF
6
ON
ON
ON
ON
Summary of Contents for YCUL0020
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