Hot Gas Reheat Startup - Lennox LCH Series Installation Instructions Manual

SCR Electric Heat Controller (LCH Units)
Optional factory-installed SCR (A38) will provide small
amounts of power to the electric heat elements to
efficiently maintain warm duct air temperatures when
there is no heating demand. The SCR maintains duct
air temperature based on input from a field-provided
and installed thermostat (A104) and duct sensor
(RT20). SCR is located in the compressor section on
the left wall. Use only with a thermostat or specified
DDC control system.
Use the instructions provided with the thermostat to set
DIP switches as follows: S1 On, S2 Off, S3 Off. Use the
instructions provided with the duct sensor to install sensor
away from electric element radiant heat and in a location
where discharge air is a mixed average temperature.
Once power is supplied to unit, zero SCR as follows:
1- Adjust thermostat (A104) to minimum position.
2- Use a small screwdriver to slowly turn the ZERO
potentiometer on the SCR until the LED turns solid red.
3- Very slowly adjust the potentiometer the opposite
direction until the LED turns off.
Hot Gas Reheat Start-Up And Operation
General
Hot gas reheat units, available on standard and high
efficiency units only, 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 28 for
reheat refrigerant routing and figure 29 for standard
cooling refrigerant routing.
L14 Reheat Coil Solenoid Valve
When Unit Controller input (Unit Controller J298-5 or
J299-8) indicates
dehumidification, L14 reheat valve is energized (Unit
Controller P269-3) and refrigerant is routed to the
reheat coil.
LGH/LCH036, 048, 060, 072, 074
room conditions require
Reheat Setpoint
Reheat is factory-set to energize when indoor relative
humidity rises above 60% (default). The reheat setpoint
can be adjusted by changing Unit Controller 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 Unit Controller key pad to elect SERVICE >
TEST > DEHUMIDIFIER.
The blower and compressor (reheat) should be
operating. DEHUMIDIFIER 1 ON will be appear on the
Unit Controller display.
4- Press BACK on the Unit Controller display to stop the
testing mode.
Compressor (reheat) and blower should de-energize.
Default Reheat Operation
During reheat mode free cooling is locked out.
No Y1 demand but a call for dehumidification:
Compressor is operating, blower is on, and the reheat
valve is energized.
Y1 demand:
Compressor is operating, blower is on, and the reheat
valve is energized.
Y2 demand:
Compressor is operating, blower is on, and the reheat
valve is de-energized.
Page 65