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OPERATION MODES
Operation Modes
Initialization
The MHGRV-X Controller uses on-board LEDs to indicate various
diagnostic conditions during power-up and operation. It also uses the
LCD Display to show initialization. Please review this information
for a complete description of the controller initialization sequence.
Modulating Hot Gas Valves
The MHGRV-X Controller utilizes two modulating valves to control
the fl ow of Hot Gas through the Hot Gas Reheat Coil. One of these
valves is the Condenser Hot Gas Valve and the other is the Reheat
Hot Gas Valve. The valves are wired to the MHGRV-X Controller
Modulating Hot Gas Valve Output terminals on the controller. These
valves work in concert with each other to create a "three-way valve"
confi guration. As one closes, the other opens, etc. All modes of opera-
tion that follow referring to the Hot Gas Reheat Valve are actually
a combination of these two valves working together to achieve the
specifi ed sequence of operation.
valve instead of two separate valves. The three way valve is wired
to the Reheat terminal block.
Modes of Operation
The MHGRV-X Controller can be used in two diff erent modes of op-
eration. These modes behave in a similar manner; the main diff erence
is the way they receive information to control the dehumidifi cation
process. The following is a description of these modes:
Stand-Alone Operation
As the name implies, in this mode the controller behaves as an in-
dependent unit. The controller begins the dehumidifi cation process
when the Dehumidifi cation Input "H1" receives a 24 VAC signal
from an outside source. When the signal is received, the controller
will activate the "FAN" output to energize the HVAC unit fan. At the
same time, the controller will initiate Cooling Mode by energizing
the "CMP" output starting the HVAC unit compressor. In addition,
the controller will open the Hot Gas Reheat Coil by activating the
"VALVE" output. At this time, the MHGRV-X Controller will start
to modulate the Modulating Hot Gas Reheat valve. The control-
ler will modulate the MHGR valve to maintain the Supply Air
Temperature Setpoint by activating the stepper motor outputs on
the MHGR valve. The Supply Air Setpoint is confi gured with the
Setpoint Screen in the LCD Display. If Supply Air Temperature
Reset is used, it will initiate when a 0-10 VDC signal is supplied to
8
NOTE:
Some units use a three way
the "RESET IN" input. As the voltage increases from 0 to 10 Volts
at the "RESET IN" input, the Supply Air Temperature will be reset
towards the Supply Air Reset Temperature Setpoint. This setpoint
is confi gured with the Setpoint Screen in the LCD Display. When
a 10 Volt input signal is received at the "RESET IN" input, it will
be controlling at the Supply Air Temperature Reset Setpoint. The
controller will conclude the Dehumidifi cation process when input
"H1" is deactivated, the input "Cool Override" is activated, or the
input "Heat Override" is activated.
Auxiliary Mode Stand-Alone
1. Auxiliary Mode Operation needs to be confi gured fi rst from
the display.
2. This mode will be activated if the Reheat Enable input is
enabled.
Any expansion boards that are enabled will follow.
3. Reheat Valve
• The unit will keep the valve off for the fi rst 30 seconds
• Then it will modulate the valve between 0% to 100% to
match the 0-10 VDC Auxiliary Analog input.
4. The Unit will exit Reheat Mode when the Reheat input is
disabled. The expansion modules will do the same.
5. Relay Operation
• Fan Relay will be activated in this mode.
• Compressor Relay will be activated in this mode.
• Valve Relay will be activated in this mode after
the initial 30 seconds.
• Auxiliary relay
•
It will be activated if the Reheat Valve stays at 100%
for 2 minutes and the Supply Air Temperature is 5°F
below the Supply Air Setpoint.
•
It will deactivate if the Reheat Valve stays at 0%
for 2 minutes and the Supply Air Temperature is
5°F above the Supply Air Setpoint.
MHGRV-X Field Technical Guide
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