Page 40
VII-FACTORY-INSTALLED Hot Gas Re-Heat
General
Hot gas reheat units provide a dehumidifying mode of op
eration. These units contain a reheat coil adjacent to and
downstream of the evaporator coil. Reheat coil solenoid
valves, L14 and L30, route hot discharge gas from the
compressor to the reheat coil. Return air pulled across the
evaporator coil is cooled and dehumidified; the reheat coil
adds heat to supply air.
See figure 21 for 156 and 180 reheat refrigerant routing, fig
ure 22 for 156 and 180 normal cooling refrigerant routing,
figure 23 for 210, 240, and 300 reheat refrigerant routing
and figure 24 for 210, 240, and 300 normal cooling refriger
ant routing.
L14 and L30 Reheat Coil Solenoid Valves
When Unit Controller (P298-5 or J299-8) indicates room
conditions require dehumidification, reheat valves L14 and
L30 are energized (Unit Controller J394-1 or J394-3) and
refrigerant is routed to the reheat coil.
Reheat Setpoint
Reheat is factory-set to energize when indoor relative hu
midity rises above 60% (default). The reheat setpoint can
be adjusted by changing mobile service app Settings - Con
trol menu. A setting of 100% will operate reheat from an en
ergy management system digital output. The reheat set
point can also be adjusted using an optional Network
Control Panel (NCP).
Reheat will terminate when the indoor relative humidity falls
3% (57% default) or the digital output de-energizes. The re
heat deadband can be adjusted at Settings - Control menu.
A91 Humidity Sensor
Relative humidity should correspond to the sensor (A91)
output voltage listed in table 18. For example: if indoor air
relative humidity is 80% +
3%, the humidity sensor output
should read 8.00VDC.
Check the sensor output annually for accuracy. Keep the air
intake openings on the sensor clean and free of obstruc
tions and debris.
TABLE 18
Relative Humidity (%RH + 3%) Sensor Output (VDC)
20 2.00
30 3.00
40 4.00
50 5.00
60 6.00
70 7.00
80 8.00
90 9.00
Check-Out
Test hot gas reheat operation using the following proce
dure.
1. Make sure reheat is wired as shown in wiring section.
2. Make sure unit is in local thermostat mode.
3. Use mobile service app (the QR is located in the control
area) menu path to select:
SERVICE > TEST > DEHUMIDIFIER
The blower, compressor 1 and compressor 2 (reheat)
should be operating. Reheat mode will appear on the mo
bile service app display.
4. Deselect:
SERVICE > TEST > DEHUMIDIFIER
Compressor 1 and 2 (reheat) should de-energize, blower
should still be energized.
Default Reheat Operation
Reheat will operate as shown in table 19 once this condition
is met:
1. System must NOT be operating in heating mode.
IMPORTANT - Free cooling does not operate during re
heat.
For other reheat control options, refer to the Unit Controller
manual.
Additional Cooling Stages
Units are shipped from the factory to provide two stages of
cooling.
Compressors are not de-energized when unit operation
changes from cooling to reheat or from reheat to cooling.
Instead, L14 and L30 reheat valves are energized (reheat)
or de-energized (cooling).
NOTE - Another thermostat staging option is available
which allows both compressors to be energized during free
cooling. See Unit Controller manual for details.
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