Operation Modes - AAON MHGRV-X Field Technical Manual

OPERATION MODES

Modes of Operation
AUX: Two-Position HGR Valve / Reversing
Valve
If configured as standard, this relay will be used to control a
two-position HGR valve. Used on larger capacity systems that
have an optional two-position HGR Valve in addition to the
Modulating HGR Valve. When a call for Dehumidification is
received, if the modulating HGR valve is at 100% and the Supply
Air Temperature is at least 5°F below setpoint, this relay output
will energize to enable the two-position HGR valve. The relay
will de-energize when the modulating HGR valve closes to 0%
and the Supply Air Temperature is at least 5°F above setpoint.
The modulating valve is then enabled to modulate to maintain
the Supply Air Temperature Setpoint.
If configured as Reversing Valve, this relay will control a
Reversing Valve on a Heat Pump unit. Any time there is a call
for Cooling or Dehumidification, this relay will be energized.
COM: Relay Common
Requires 24 VAC from transformer.
Initialization
The MHGRV-X 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 utilizes two modulating valves to control the
flow of Hot Gas through the Hot Gas Reheat Coil. One of these
valves is the Condenser Hot Gas Valve and the other is the
Hot Gas Reheat Valve. The valves are wired to the MHGRV-X
Modulating Hot Gas Valve Output terminals. These valves
work in concert with each other to create a "three-way valve"
configuration. As one closes, the other opens, etc. All modes of
operation that follow referring to the Hot Gas Reheat Valve are
actually a combination of these two valves working together to
achieve the specified sequence of operation.
Some units use a three-way valve instead of two
NOTE:
separate valves. The three way valve is wired to the
Reheat terminal block.
10
Modes of Operation
The MHGRV-X can be used in two different modes of operation.
These modes behave in a similar manner; the main difference is
the way they receive information to control the dehumidification
process. The following is a description of these modes:
Stand-Alone Operation
As the name implies, in this mode the controller behaves as an
independent unit. The controller begins the dehumidification
process when the Dehumidification 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 will start to modulate the Modulating Hot
Gas Reheat Valve. The controller 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 configured 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 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 configured 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 Dehumidification 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 configured first
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 first 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.
MHGRV-X Field Technical Guide