2
GENERAL
2-Speed Indoor Fan Motor Indoor Fan Speed System
The 2-Speed Indoor Fan Motor system utilizes a Fan Speed con-
trol board and Variable Frequency Drive (VFD) to automatically
adjust the indoor fan motor speed in sequence with the unit’s ven-
tilation, cooling and heating operation. Per ASHRAE 90.1-2016
and IECC
1
-2015 standards, during the first stage of cooling opera-
tion the 2-Speed Indoor Fan Motor system will adjust the fan mo-
tor to provide 66% of the design airflow rate for the unit. When
the call for the second stage of cooling is required, the 2-Speed In-
door Fan Motor system will allow the design airflow rate for the
unit established (100%). During the heating mode, the 2-Speed In-
door Fan Motor system will allow total design airflow rate (100%)
operation. During ventilation mode, the 2-Speed Indoor Fan Mo-
tor system will operate the fan motor at 66% of full speed.
Figures 1, 2 and 3 show the VFDs used for the 2-Speed Indoor
Fan Motor indoor fan speed system.
Fig. 1 — ACH550 Variable Frequency Drive (VFD)
Fig. 2 — ACS320 Variable Frequency Drive (VFD)
Fig. 3 — ACH580 Variable Frequency Drive (VFD)
Identifying Factory Option
This supplement only applies to units that meet the criteria de-
tailed in Table 1. If the unit does not meet that criteria, discard this
document.
NOTE: See Fig. 4 and 5 for examples of typical Model Number
Nomenclature.
Unit Installation with 2-Speed Indoor Fan Motor Option
581J/551J, 548J/549J AND 580J/558J ROOFTOP
Refer to the base unit installation instructions for standard required
operating and service clearances.
1. Third-party trademarks and logos are the property of their respective
owners.
Table 1 — Model Size/VFD Option Indicator
MODEL/SIZES
POSITION IN
MODEL NUMBER
VFD FIOP
INDICATOR
580J/558J / 07-30 17 D-E
548J / 07-24 17 D-E
581J/551J / 07-28 17 D-E
549J / 07-12 17 D-E
524J*07-30A 92
524J*07-25H 92
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