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LGM/LCM036, 048, 060, 074
Hot Gas Reheat Start-Up And Operation
General
Hot gas reheat units provide a dehumidifying mode of
operation. These units contain a reheat coil adjacent
to and downstream of the evaporator coil. Reheat coil
solenoid valve, L14, routes 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 25 for
reheat refrigerant routing and figure 26 for standard
cooling refrigerant routing.
L14 Reheat Coil Solenoid Valve
When Unit Controller input (Unit Controller J298-5 or
J299-8) indicates room conditions require
dehumidification, L14 reheat valve is energized (Unit
Controller P269-3) and refrigerant is routed to the
reheat coil.
Reheat Setpoint
Reheat is factory-set to energize when indoor relative
humidity rises above 60% (default). The reheat setpoint
can be adjusted by changing mobile service app Settings
- Control menu. A setting of 100% will operate reheat from
an energy management system digital output. The reheat
setpoint 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 reheat deadband can be adjusted at Settings -
Control menu.
Check-Out
Test reheat operation using the following procedure.
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 menu path to select
SERVICE > TEST > DEHUMIDIFIER.
The blower, compressor, and reheat valve should be
energized. Pressure can be checked on the reheat line
pressure tap. Pressure on the reheat line should match
discharge pressure closely in reheat mode.
Default Reheat Operation
During reheat mode free cooling is locked out.
A-Thermostat Mode With 24V Humidistat
No Y1 demand but a call for dehumidification:
Compressor operates at 100%, blower and outdoor
fan modulate to maintain indoor coil and discharge air
temperatures, reheat valve is energized.
Y1 demand:
Compressor is modulating, blower is on low, and the
reheat valve is de-energized.
Y2 demand:
Compressor is modulating, blower is on high, reheat
valve is de-energized.
B-Thermostat Mode With Zone RH Sensor
No Y1 demand but a call for dehumidification:
Compressor modulates based on zone relative
humidity, blower and outdoor fan modulate to
maintain indoor coil and discharge air temperatures,
reheat valve is energized.
Y1 and dehumidification demand:
Compressor is modulating, blower is on low, and the
reheat valve is de-energized.
Y2 and dehumidification demand:
Compressor is modulating, blower is on high, reheat
valve is de-energized.
C-Zone Sensor Mode With Humidistat
No cooling demand but a call for dehumidification:
Compressor operates at 100%, blower and outdoor
fan modulate to maintain indoor coil and discharge air
temperatures, reheat valve is energized.
Cooling and dehumidification demand:
Compressor is modulating, blower is modulating,
reheat valve is de-energized.
D-Zone Sensor Mode With Zone RH Sensor
No cooling demand but a call for dehumidification:
Compressor modulates based on zone relative
humidity, blower and outdoor fan modulate to
maintain indoor coil and discharge air temperatures,
reheat valve is energized.
Cooling and dehumidification demand:
Compressor is modulating, blower is modulating, and
the reheat valve is de-energized.
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