AAON MHGRVX-B2 Quick start guide

MHGRVX-B2 Module
Field Technical Guide
Designed to work exclusively with Sanhua EBV05H reheat valves
D15
J3
MODGASx
MODGAS
NORMAL
R59
R60
R60
U9
C46
R61
R75
SAT OPTIONS
SAT
GND
290
AOUT
GND
COOL OVRD
HEAT OVRD
REHEAT EN
RESET IN
AUX IN
GND
TB3
C18
R18
F1
V2
V3 V1
LC
FAN
COMP
VALVE
AUX
COMMON
TB2
STATUS
ALARM
COMM
POWER
CONDENSOR DRIVE
BLACK
WHITE
RED
GREEN
OPENING TB4
REHEAT DRIVE
BLACK
WHITE
GREEN
RED
OPENING TB5
C23
.01uF
SERIAL #
DISPLAY
R49
R48
R44
R42
R9
R4
U8
C38
R7
R8
C43
R6
10
ALARM
UP
ENTER
MENU
DOWN
www.aaon.com
AAON P/N: ASM06927
MHGRVX-B2
FAN
COMPRESSOR
CONDENSER
DRIVE TERMINALS
REHEAT VALVE
DRIVE TERMINALS
REHEAT VALVE
AUX
BLACK
GND
AUX INPUT (AI)
RESET SIG (AI)
RHT EN (BI)
SAT (AI)
0-10V VLV (AO)
HEAT OVR (BI)
COOL OVR (BI)
GND
GND
BLACK
WHITE
WHITE
RED
RED
GREEN
GREEN
COMMON
RELAY
OUTPUTS
INPUT/OUTPUT TERMINALS (TYPE)
CONTACT
RATING IS
1 AMP MAX
@ 24 VAC
GND
+24 VAC
LABEL P/N:
G112610
E-BUS
CONNECT
E-BUS
CONNECT

2MHGRVX-B2 Module Technical Guide
MHGRVX-B2 REVISION LOG
REVISION AND DATE CHANGE
Rev. A, August 5, 2022 Original
AAON
2425 South Yukon Ave.
Tulsa, OK 74107-2728
www.aaon.com
Factory Technical Support Phone: [phone]
AAON Controls Support: 866-918-1100
It is the intent of AAON to provide accurate and current product
information. However, in the interest of product improvement,
AAON reserves the right to change pricing, specications, and/
or design of its product without notice, obligation, or liability.
AAON P/N: G112890, Rev. A
© August 2022 AAON Inc. All rights reserved throughout
the world.
AAON®is a registered trademark of AAON, Inc., Tulsa, OK.
AAON assumes no responsibility for errors or omissions in
this document.
This document is subject to change without notice.
www.aaon.com
MHGRVX-B2 PARTS REFERENCE
PART DESCRIPTION PART NUMBER
MHGRV-X ASM01670
MHGRVX-A1 / MHGRVX-B1 Module (no I2C) ASM07265 / ASM06910
MHGRVX-A2 / MHGRVX-B2 Module
(no I2C, Sanhua EBV05H valve only) ASM06926 / ASM06927
MODGAS-X ASM01668
MODGAS-XWR2 ASM01695
MODGAS-XWR2-B ASM06909
VCCX2 Controller ASM01698
AAON Unit Controller Varies
Supply Air Temperature Sensor G051240 (6”) G051250 (12”)
Reheat Expansion Module ASM01687
E-BUS Cable Assembly E-BUS Power and Comm 1.5 ft., 3 ft., 10 ft.,
25 ft., 50 ft., 75 ft., 100 ft., 150 ft., 250 ft., and 1000 ft. spool
G029440 (1.5 ft.), G012870 (3 ft.), G029460 (10 ft.), G045270 (25 ft.),
G029510 (50 ft.), G029530 (75 ft.), G029450 (100 ft.), G029470 (150 ft.),
V36590 (250 ft.), G018870 (1,000 ft. spool)
This manual is available for download from
www.aaon.com/library.

3MHGRVX-B2 Module Technical Guide
TABLE OF CONTENTS
OVERVIEW ......................................................................................................................................................... 5
MHGRVX-B2 General Information.......................................................................................................................... 5
WIRING ............................................................................................................................................................... 6
Installation and Wiring............................................................................................................................................. 6
MHGRVX-B2 to AAON Unit Controller Wiring......................................................................................................... 7
MHGRVX-B2 Stand-Alone Wiring........................................................................................................................... 8
INPUTS AND OUTPUTS ................................................................................................................................... 9
Inputs ...................................................................................................................................................................... 9
Outputs ................................................................................................................................................................. 10
OPERATION MODES ...................................................................................................................................... 11
Modes of Operation ...............................................................................................................................................11
Additional Features ............................................................................................................................................... 13
LCD SCREENS ................................................................................................................................................ 14
Navigation Keys .................................................................................................................................................... 14
Main Screens Map and Main MHG REHEAT Screens ......................................................................................... 15
Status and Alarm Screens .................................................................................................................................... 16
Setpoint and Force Valves Screens...................................................................................................................... 17
Protected Screens ................................................................................................................................................ 18
TROUBLESHOOTING ..................................................................................................................................... 21
LED Diagnostics ................................................................................................................................................... 21
Alarms................................................................................................................................................................... 22
Other Checks ........................................................................................................................................................ 23
APPENDIX A: SAT SENSOR .......................................................................................................................... 25
Supply Air Temperature Sensor Installation .......................................................................................................... 25
SAT Sensor Wiring Guide and Jumper Settings ................................................................................................... 26
APPENDIX B: COMPATIBILITY ..................................................................................................................... 27
MHGRVX Series Drop-In Replacement................................................................................................................ 27
APPENDIX C: REHEAT EXPANSION MODULE .......................................................................................... 28
Features and Dimensions ..................................................................................................................................... 28
Installation and Wiring........................................................................................................................................... 29
Wiring.................................................................................................................................................................... 30
Operation Modes .................................................................................................................................................. 31
LED Diagnostics and Troubleshooting.................................................................................................................. 32
APPENDIX D: FREQUENTLY ASKED QUESTIONS ................................................................................... 33
Troubleshooting .................................................................................................................................................... 33

4MHGRVX-B2 Module Technical Guide
FIGURES AND TABLES
TABLES
Table 1: MHGRVX-B2 Electrical and Environmental Requirements ........................................................................ 6
Table 2: MHGRVX-B2 Inputs and Outputs .............................................................................................................. 9
Table 3: Navigation Key Functions......................................................................................................................... 14
Table 4: STATUS LED Blink Codes........................................................................................................................ 21
Table 5: ALARM LED Blink Codes......................................................................................................................... 21
Table 6: 0-3V Temperature Sensor - Voltage and Resistance for Type III Sensors ............................................... 23
Table 7: 0-5V Temperature Sensor - Voltage and Resistance for Type III Sensors ............................................... 24
Table 8: SAT Wiring Conditions.............................................................................................................................. 26
Table 9: Reheat Expansion Module ALARM LED Blink Codes.............................................................................. 31
FIGURES
Figure 1: MHGRVX-B2 Dimensions..........................................................................................................................5
Figure 2: MHGRVX-B2 to AAON Unit Controller Wiring ...........................................................................................7
Figure 3: MHGRVX-B2 Stand-Alone Wiring..............................................................................................................8
Figure 4: LCD Display and Navigation Keys ...........................................................................................................14
Figure 5: MHGRVX-B2 LED Locations and Descriptions........................................................................................22
Figure 6: Supply Air Temperature Sensor Installation .............................................................................................25
Figure 7: Reheat Expansion Module Dimensions ...................................................................................................27
Figure 8: Reheat Expansion Module(s) Wiring .......................................................................................................29
Figure 9: Reheat Expansion LED Locations and Descriptions ...............................................................................31

5MHGRVX-B2 Module Technical Guide
OVERVIEW
MHGRVX-B2 General Information
Overview
The MHGRVX-B2 is designed to control a Modulating Hot Gas
Reheat Valve to maintain a desired SupplyAir Temperature Setpoint.
The MHGRVX-B2 can be used as a stand-alone module or can be
used in conjunction with an AAON unit controller with E-BUS
capability.
In addition, up to seven Reheat Expansion Modules can be connected
to the MHGRVX-B2 and to each other for additional reheat valve
control.
The MHGRVX-B2 connects to an AAON unit controller or
expansion module via an E-BUS cable.
CAUTION: This module only works as intended with the
Sanhua EBV05H reheat valve. See Appendix
B, page 27, for MHGRVX series compatibility.
NOTE: This module does not support I2C connections.
Features
The MHGRVX-B2 provides the following:
• Can be operated as a stand-alone module or communicating
with AAON unit controllers.
• Provides for Supply Air Temperature Setpoint reset when
required.
• Second stage reheat capability when using two hot gas
reheat valves.
• Control of the reheat solenoid valve to provide coil ushing
for positive refrigerant oil return.
• Can provide further reheat control using up to seven Reheat
Expansion Modules.
• Contains a 2 x 8 LCD character display and four buttons
that allow for status display, setpoint changes, and
conguration changes
Figure 1: MHGRVX-B2 Dimensions
5.73
2.62
2.04
4.09
0.57
0.21
5.04 5.63
5.24
NOTE: Depth is 1.50 inches.
NOTE: All dimensions are in inches.
D15
J3
MODGASx
MODGAS
NORMAL
R59
R60
R60
U9
C46
R61
R75
SAT OPTIONS
SAT
GND
290
AOUT
GND
COOL OVRD
HEAT OVRD
REHEAT EN
RESET IN
AUX IN
GND
TB3
C18
R18
F1
V2
V3 V1
LC
FAN
COMP
VALVE
AUX
COMMON
TB2
STATUS
ALARM
COMM
POWER
CONDENSOR DRIVE
BLACK
WHITE
RED
GREEN
OPENING TB4
REHEAT DRIVE
BLACK
WHITE
GREEN
RED
OPENING TB5
C23
.01uF
SERIAL #
DISPLAY
R49
R48
R44
R42
R9
R4
U8
C38
R7
R8
C43
R6
10
ALARM
UP
ENTER
MENU
DOWN
www.aaon.com
AAON P/N: ASM06927
MHGRVX-B2
FAN
COMPRESSOR
CONDENSER
DRIVE TERMINALS
REHEAT VALVE
DRIVE TERMINALS
REHEAT VALVE
AUX
BLACK
GND
AUX INPUT (AI)
RESET SIG (AI)
RHT EN (BI)
SAT (AI)
0-10V VLV (AO)
HEAT OVR (BI)
COOL OVR (BI)
GND
GND
BLACK
WHITE
WHITE
RED
RED
GREEN
GREEN
COMMON
RELAY
OUTPUTS
INPUT/OUTPUT TERMINALS (TYPE)
CONTACT
RATING IS
1 AMP MAX
@ 24 VAC
GND
+24 VAC
LABEL P/N:
G112610
E-BUS
CONNECT
E-BUS
CONNECT

6MHGRVX-B2 Module Technical Guide
WIRING
Installation and Wiring
Installation and Mounting
The MHGRVX-B2 is housed in a plastic enclosure. It is designed
to be mounted by using the three mounting holes in the enclosure
base. It is important to mount the module in a location that is free
from extreme high or low temperatures, moisture, dust, and dirt. Be
careful not to damage the electronic components when mounting
the module.
NOTE: The MHGRVX-B2 contains no user-serviceable
parts. Contact qualied technical personnel if your
controller or module is not operating correctly.
Wiring
The modules must be connected to an 18-30 VAC power source
of the proper size for the calculated VA load requirements. All
transformer sizing should be based on the VA ratings listed in Table
1, this page.
NOTE: If the temperature at the MHGRVX-B2 is below
-4ºF (-20ºC), the display refresh rate could be less
responsive.
WARNING: When using a single transformer to power more
than one controller, module, or expansion
module, the correct polarity must always be
maintained between the boards. Failure to
observe correct polarity will result in damage
to the unit controller, MHGRVX-B2, and any
associated modules.
Please carefully read and apply the following information when
wiring the unit controller, MHGRVX-B2 and any associated module.
1. All wiring is to be in accordance with local and national
electrical codes and specications.
2. All 24 VAC wiring must be connected so that all ground
wires remain common. Failure to follow this procedure
can result in damage to the controller and connected
devices.
3. Minimum wire size for 24 VAC wiring should be
18-gauge.
4. Minimum wire size for all sensors should be 24-gauge.
Some sensors require two-conductor wire and some
require three-or four-conductor wire.
5. Minimum wire size for 24 VAC thermostat wiring should
be 22-gauge.
6. Be sure that all wiring connections are properly inserted
and tightened into the terminal blocks. Do not allow wire
strands to stick out and touch adjoining terminals which
could potentially cause a short circuit.
7. When communication wiring is to be used to interconnect
HVAC unit controllers together or to connect to other
communication devices, all wiring must be plenum-
rated, minimum 18-gauge, two-conductor, twisted pair
with shield. AAON can supply communication wire that
meets this specication and is color coded for the network
or local loop. Please consult your AAON distributor for
information. If desired, Belden #82760 or equivalent wire
may also be used.
8. Before applying power to the HVAC unit controller,
MHGRVX-B2, and any associated modules, be sure
to recheck all wiring connections and terminations
thoroughly.
Powering Up
When the controller and/or modules are rst powered up, the
POWER LED should light up and stay on continuously. If it does
not light up, check to be sure that you have 24 VAC connected to
the controller, that the wiring connections are tight, and that they are
wired for the correct polarity. The 24 VAC power must be connected
so that all ground wires remain common. If after making all these
checks, the POWER LED does not light up, please contact AAON
Controls Support for assistance.
Control
Device
Voltage
VA Load
Operating
Temperature
Humidity
(Non-
Condensing)
MHGRVX-B2
18-30VAC 18 -22°F to 158°F*
-30ºC to 70ºC* 0-95% RH
Inputs
Resistive Inputs require 10KΩ
Type 3 Thermistor
24VAC Inputs provide 4.7KΩ
Load
Outputs Relay Outputs: 1 Amp
maximum per output.
Table 1: MHGRVX-B2 Electrical and Environmental
Requirements

7MHGRVX-B2 Module Technical Guide
WIRING
MHGRVX-B2 to AAON Unit Controller Wiring
Communications Wiring
For connection to a VCCX2 or VCB-X Controller, VCCX2 or
VCB-X Expansion Module, and Reheat Expansion Module, use
an E-BUS cable to connect to the appropriate E-BUS port on those
modules and/or controller.
When connected to an AAON unit controller, the Supply Air
Temperature Sensor is attached to the AAON unit controller.
See Figure 2, this page.
See the SAT Wiring Conditions and SAT OPTIONS jumper settings
in Tables 8 and 10, page 26.
Figure 2: MHGRVX-B2 to AAON Unit Controller Wiring
GND
RED
GRN
WHT
BLK
Condenser Valve #1
HGR Valve #1
RED
GRN
WHT
BLK
Compressor
Flush Active Signal
Two Position HGR Valve
(Optional)
C1
C2
COMM
RED
GRN
WHT
BLK
Mount in Supply
Air Duct
Supply Air
Temperature
Sensor
Supply Air Temperature Sensor
connects to AI3 and GND on the
VCCX2 Controller
Set jumper to
NORMAL
E-BUS cable connects to
the VCCX2 expansion port
E-BUS cable connects to the
Reheat Expansion Module
Line
Voltage
40 VA transformer
minimum
18-30 VAC
Fan
Alternate configuration for
three-way valve
R2
D15
J3
MODGASx
MODGAS
NORMAL
R1 SAT OPTIONS
AOUT
GND
0-10 VDC Signal
(optional)
R59
R60
R60
U9
C46
R61
R75
SAT
GND
290
COOL OVRD
HEAT OVRD
REHEAT EN
RESET IN
AUX IN
GND
TB3
C18
R18
F1
V2
V3 V1
LC
FAN
COMP
VALVE
AUX
COMMON
TB2
STATUS
ALARM
COMM
POWER
CONDENSOR DRIVE
BLACK
WHITE
RED
GREEN
OPENING TB4
REHEAT DRIVE
BLACK
WHITE
GREEN
RED
OPENING TB5
C23
.01uF
SERIAL #
DISPLAY
R49
R48
R44
R42
R9
R4
U8
C38
R7
R8
C43
R6
10
ALARM
UP
ENTER
MENU
DOWN
www.aaon.com
AAON P/N: ASM06927
MHGRVX-B2
FAN
COMPRESSOR
CONDENSER
DRIVE TERMINALS
REHEAT VALVE
DRIVE TERMINALS
REHEAT VALVE
AUX
BLACK
GND
AUX INPUT (AI)
RESET SIG (AI)
RHT EN (BI)
SAT (AI)
0-10V VLV (AO)
HEAT OVR (BI)
COOL OVR (BI)
GND
GND
BLACK
WHITE
WHITE
RED
RED
GREEN
GREEN
COMMON
RELAY
OUTPUTS
INPUT/OUTPUT TERMINALS (TYPE)
CONTACT
RATING IS
1 AMP MAX
@ 24 VAC
GND
+24 VAC
LABEL P/N:
G112610
E-BUS
CONNECT
E-BUS
CONNECT

8MHGRVX-B2 Module Technical Guide
WIRING
MHGRVX-B2 Stand-Alone Wiring
Stand-Alone Wiring
In Stand-Alone Mode, the MHGRVX-B2 connects to the E-BUS
port of the Reheat Expansion Module with an E-BUS cable. See
Figure 3, this page.
See the SAT Wiring Conditions and SAT OPTIONS Jumper Settings
in Tables 8 and 9, page 26.
Figure 3: MHGRVX-B2 Stand-Alone Wiring
GND
RED
GRN
WHT
BLK
Condenser Valve #1
HGR Valve #1
RED
GRN
WHT
BLK
Compressor
Flush Active Signal
or Compressor 2
Two Position HGR Valve
or Reversing Valve
C1
C2
COMM
Line
Voltage
40 VA
transformer
minimum
18-30 VAC
Fan
+
-
0-10 VDC
External Reset
Signal
H1 (Dehumidification)
Heating Override
Cooling Override
Mount in
Supply Air
Duct
Supply Air
Temperature
Sensor
E-BUS cable connects to the
Reheat Expansion Module
0-10 VDC Signal
(optional)
Set
jumper to
NORMAL
NOTE:
Only one Supply Air Temperature
Sensor can be used per application.
D15
J3
MODGASx
MODGAS
NORMAL
R59
R60
R60
U9
C46
R61
R75
SAT OPTIONS
SAT
GND
290
AOUT
GND
COOL OVRD
HEAT OVRD
REHEAT EN
RESET IN
AUX IN
GND
TB3
C18
R18
F1
V2
V3 V1
LC
FAN
COMP
VALVE
AUX
COMMON
TB2
STATUS
ALARM
COMM
POWER
CONDENSOR DRIVE
BLACK
WHITE
RED
GREEN
OPENING TB4
REHEAT DRIVE
BLACK
WHITE
GREEN
RED
OPENING TB5
C23
.01uF
SERIAL #
DISPLAY
R49
R48
R44
R42
R9
R4
U8
C38
R7
R8
C43
R6
10
ALARM
UP
ENTER
MENU
DOWN
www.aaon.com
AAON P/N: ASM06927
MHGRVX-B2
FAN
COMPRESSOR
CONDENSER
DRIVE TERMINALS
REHEAT VALVE
DRIVE TERMINALS
REHEAT VALVE
AUX
BLACK
GND
AUX INPUT (AI)
RESET SIG (AI)
RHT EN (BI)
SAT (AI)
0-10V VLV (AO)
HEAT OVR (BI)
COOL OVR (BI)
GND
GND
BLACK
WHITE
WHITE
RED
RED
GREEN
GREEN
COMMON
RELAY
OUTPUTS
INPUT/OUTPUT TERMINALS (TYPE)
CONTACT
RATING IS
1 AMP MAX
@ 24 VAC
GND
+24 VAC
LABEL P/N:
G112610
E-BUS
CONNECT
E-BUS
CONNECT

9MHGRVX-B2 Module Technical Guide
INPUTS AND OUTPUTS
Inputs
I/O Map
The following inputs and outputs are available on the MHGRVX-B2.
See Table 2, this page to reference the input and outputs.
NOTE: All analog and 24 VAC contact closure inputs are
used only in Stand-Alone Mode.
Table 2: MHGRVX-B2 Inputs and Outputs
Analog Inputs
SAT: Supply Air Temperature Sensor
Used in Stand-Alone Mode and when MODGAS is connected.
The Supply Air Temperature Sensor is the main control input.
This sensor has to be installed for the unit to operate. The Supply
Air Temperature Sensor is located in the discharge air stream and
monitors the HVAC unit’s Supply Air Temperature to maintain the
Supply Air Temperature Setpoint.
RST IN: Reset Signal
Used only in Stand-Alone Mode. The Discharge Temperature
Setpoint can be reset by supplying a 0-10 VDC signal to the RESET
IN low voltage terminal block. This reset signal is optional and need
only be used if you require resetting of the discharge air temperature.
AUX IN: Auxiliary Reheat Valve Input
Used when AUX mode is congured as enabled. This input looks
at a 0-10 VDC signal to control the valve position.
• 0VDC = 0% Reheat Valve position
• 5VDC = 50% Reheat Valve position
• 10VDC = 100% Reheat Valve position.
Analog Outputs
0-10V VLV: 0-10 VDC Valve Signal
Used when controlling a valve that uses a 0-10 volt signal to drive it.
Binary Inputs
REHEAT EN: Reheat Enable Contact
Used only in Stand-Alone Mode. When a call for dehumidication is
initiated by another controller, this interlocked 24 VAC wet contact
closure is used to enable the MHGRVX-B2.
HEAT OVR: Heating Override
Used only in Stand-Alone Mode. When a call for heating is initiated
by the HVAC unit, this interlocked 24 VAC wet contact closure is
used to override the MHGRVX-B2 Dehumidication Mode.
COOL OVR: Cooling Override
Used only in Stand-Alone Mode. When a call for cooling is initiated
by the HVAC unit, this interlocked 24 VAC wet contact closure is
used to override the MHGRVX-B2 Dehumidication Mode.
ANALOG INPUTS
1Supply Temperature
2Reset Signal
3AUX Input
ANALOG OUTPUTS
1 0-10 VDC Valve Signal
BINARY INPUTS
1Reheat Enable
2Heating Override
3Cooling Override
RELAYS
1Fan
2Compressor
3Flush Active Signal / Compressor 2
4Auxiliary / Reversing Valve

10MHGRVX-B2 Module Technical Guide
INPUTS AND OUTPUTS
Outputs
Relay Outputs
FAN: Fan Enable
When a call for Dehumidication, Cooling Override, or Heating
Override is received, this relay will be closed to energize the HVAC
unit Supply Fan.
CMP: Compressor Enable
When a call for Dehumidication or Cooling Override is received,
this relay will be closed to energize the Compressor(s).
VALVE: Flush Active Signal / Compressor 2
If congured as Flush, this relay will be active any time a Flush
Cycle is active. When the Flush Cycle ends this relay will turn o
until the next ush occurs.
If congured as Compressor 2, this relay will be used to control
a second Compressor when there is a call for Dehumidication.
Compressor 2 will come on 30 seconds after the rst Compressor
activates. Compressor 2 has a minimum run time of 10 minutes,
and will turn o if the Reheat Valve is at 100% and the Supply Air
Temperature is 5°F below setpoint for one minute. After being o
for 10 minutes, it can come back on if the Supply Air Temperature
is 5°F above setpoint and the valve is at 0%.
AUX: Two-Position HGR Valve / Reversing Valve
If congured 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 Dehumidication 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 SupplyAir Temperature
is at least 5°F above setpoint.
The modulating valve is then enabled to modulate to maintain the
Supply Air Temperature Setpoint.
If congured as Reversing Valve, this relay will control a Reversing
Valve on a Heat Pump unit. Any time there is a call for Cooling or
Dehumidication, this relay will be energized.
COM: Relay Common
Requires 24 VAC from transformer.

11MHGRVX-B2 Module Technical Guide
OPERATION MODES
Modes of Operation
Initialization
The MHGRVX-B2 uses on-board LEDs to indicate various
diagnostic conditions during power-up and operation. It also uses an
LCD display to show initialization. Please review this information
for a complete description of the initialization sequence.
Modulating Hot Gas Valves
The MHGRVX-B2 utilizes two modulating valves to control the 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 Hot Gas Reheat
Valve. The valves are wired to the MHGRVX-B2 Modulating Hot
Gas Valve Output terminals. These valves work in concert with each
other to create a “three-way valve” conguration. 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 specied sequence of operation.
NOTE: Some units use a three-way valve instead of two
separate valves. The three way valve is wired to the
Reheat terminal block.
Modes of Operation
The MHGRVX-B2 can be used in two dierent modes of operation.
These modes behave in a similar manner; the main dierence is
the way they receive information to control the dehumidication
process.
Stand-Alone Mode
As the name implies, in this mode the module behaves as an
independent unit. The module begins the dehumidication process
when the Dehumidication Input “H1” receives a 24 VAC signal
from an outside source. When the signal is received, the module will
activate the “FAN” output to energize the HVAC unit fan. At the
same time, the module will initiate Cooling Mode by energizing the
“CMP” output starting the HVAC unit compressor. At this time, the
MHGRVX-B2 will start to modulate the Modulating Hot Gas Reheat
Valve. The module 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 con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 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 con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 Dehumidi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 congured 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 o for the 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.
• Auxiliary Relay
○It will be activated if the Reheat Valve stays at 100%
for two 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
two minutes and the Supply Air Temperature is 5°F
above the Supply Air Setpoint.

12MHGRVX-B2 Module Technical Guide
OPERATION MODES
Modes of Operation
Communications Operation
In this mode, the MHGRVX-B2 behaves as an expansion board for
an AAON unit controller. The controller begins the dehumidication
process when the AAON unit controller makes a request to the
MHGRVX-B2 for dehumidication. At that time, 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.
At this time, the MHGRVX-B2 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 set by programming the HVAC unit controller. If Supply
Air Temperature Reset is used, it will initiate when the HVAC unit
controller ends a request to reset the Supply Air Temperature.
The Supply Air Temperature will be reset towards the Supply Air
Reset Temperature Setpoint stored in the HVAC unit controller. It
will send a request to move towards the Supply Air Temperature
Reset Setpoint based on its setpoints and conguration.
The controller will conclude the Dehumidication process when the
HVAC unit controller sends a request to terminate Dehumidication
or a Cooling or Heating Override request is made by the HVAC unit
controller. Any setpoints or signals at the inputs to the MHGRVX-B2
will be ignored.
Auxiliary Mode Communicating
1. Same as the Stand-Alone Auxiliary Mode, but the Reheat
Enable and Auxiliary Valve position will be sent using
E-BUS commands.

13MHGRVX-B2 Module Technical Guide
OPERATION MODES
Additional Features
Additional Features
Reheat Coil Flush
To assure positive oil return to the compressor, the Hot Gas Reheat
Coil will be ushed of liquid refrigerant by moving the Modulating
Gas Reheat Valve to its maximum position for a short interval.
Cooling Flush
If the unit is in Cooling Mode, a ush will occur when the unit’s
ush cooling interval timer has elapsed. The time is accumulated
whenever it is in cooling mode and resets after each ush cycle. The
ush cooling interval timer is a setpoint that is congurable using
the keypad and display (0 to 120 minutes in 10 minute increments).
Reheat Mode Flush
If the unit is in Dehumidication Mode and the valve is below 70%
for the ush reheat interval timer value, a ush will occur. If the
valve goes above 70%, the timer is reset. The ush reheat interval
timer is a setpoint that is congurable using the keypad and display
(0 to 120 minutes in 10 minute increments).
Condenser Coil Flush
If Condenser Coil Flush is configured and the unit is in
Dehumidication Mode and the reheat valve is above 70% for the
ush reheat interval timer value, a condenser ush will occur. This
shares the timer with the reheat ush so if the valve is below 70%
a Reheat Flush would occur.
Optional Second Stage Reheat
On larger systems, where more hot gas reheat capacity may be
required, a two-position Hot Gas Reheat Valve can be connected to
the MHGRVX-B2 to be used in conjunction with the Modulating
Hot Gas Reheat Valve. Any time the reheat demand moves above
the Modulating Hot Gas Reheat Valve capacity, this two-position
valve would be energized to supply additional hot gas to the Hot Gas
Reheat Coil. As the reheat demand is satised, the MHGRVX-B2
will de-energize the two-position valve and control reheat with the
Modulating Hot Gas Reheat Valve.

14MHGRVX-B2 Module Technical Guide
LCD SCREENS
Navigation Keys
LCD Display Screen and Navigation Keys
The LCD display screens and buttons allow you to view status and
alarms, and enable force modes. See Figure 4, this page and refer
to Table 3, this page for descriptions.
Figure 4: LCD Display and Navigation Keys
Table 3: Navigation Key Functions
NAVIGATION
KEY KEY FUNCTION
MENU Use the MENU key to move through screens
within Main Menu categories and return to the
Main Menu while at other screens.
UP Use this key to adjust setpoints and change
congurations.
DOWN Use this key to adjust setpoints and change
congurations.
ENTER Use the ENTER key to navigate through the
Main Menu Screen categories.
ALARM
UP
DOWN
ENTERMENU

15MHGRVX-B2 Module Technical Guide
LCD SCREENS
Main Screens Map and Main MHG REHEAT Screens
Main Screens Map
Refer to the following map when navigating through the LCD Main
Screens. The rst screen is an initialization screen. To scroll through
the rest of the screens, press the <MENU> button.
MHGRVX
3005vXXX
Press to scroll through the main screens.
Press to go to STATUS Screens.
STATUS
MENU
Press to scroll through STATUS Screens.
Press to go to ALARMS Screens.
ALARMS
MENU
Press to scroll through ALARMS Screens.
Press to go to SETPOINTS Screens.
SETPOINT
MENU
Press to scroll through SETPOINT Screens.
Press to go to FORCE VALVE Screens.
FORCE
MENU
Press to scroll through FORCE VALVES Screens.
Main Screens
Refer to the following map when navigating through the Main
Screens. From the main screen, press <ENTER> to scroll through
the screens.
MHGRVX
3005vXXX
S/A MODE,
SA MODE LOCKED
OR COMM MODE
In Stand-Alone Mode, the screen will display S/A MODE or S/A
MODE LOCKED.
In Communications Mode, the screen will display COMM MODE
and the items below will scroll through the screen:
1. Number of good packets being received. This will roll
over after 9999. Example: +XXXX
2. Number of checksum errors. This will stop at 9999.
Example: C-XXXX
3. Number of packet length errors. This will stop at 9999
until power is cycled. Example: P-XXXX
SOFTWARE
3005vXXX
CURRENT SOFTWARE VERSION
ADDRESS
1(132)
CURRENT BOARD ADDRESS

16MHGRVX-B2 Module Technical Guide
LCD SCREENS
Status and Alarm Screens
Status Screens
Refer to the following map when navigating through the Status
Screens. From the STATUS Screen, press <ENTER> to scroll
through the screens.
STATUS
Status Screens shown below will scroll automatically if LCD
display is left on this screen for 20 seconds.
MODE
REHEAT
MODE
This screen displays the current mode of operation of the
MHGRVX-B2. The mode options are:
OFF: This mode will display if the unit is not in Dehumidication Mode
and there is no call for Modulating Hot Gas Reheat (MHGR).
REHEAT: During Dehumidication, the unit will enter the Reheat Mode
and will begin to modulate the MHGR Valve to maintain the Supply Air
Temperature Setpoint. The unit will leave the Reheat Mode when the unit
leaves the Dehumidication Mode.
FLUSH: This mode will display if the unit is performing a cooling ush
cycle or a reheat ush cycle (see Additional Features, page 13).
AUX: If Aux operation has been enabled, a 0-10 VDC signal can be
used to proportionally modulate the MHGR Valve between 0 – 100 %.
FORCE!: The unit is in the Force Mode.
VLV POS
100%
VALVE POSITION
0 to 100 percent
SA TEMP
XX.X
SUPPLY AIR TEMPERATURE
40ºF to 150ºF or 5ºC to 65ºC.
If no sensor is detected, screen will display “NO SENSR”
Alarm Screens
Refer to the following map when viewing Alarm Screens. These
screens will display automatically when alarms are present. For
more information, see pages 21 and 22.
ACTIV SP
XX.X
ACTIVE SUPPLY AIR SETPOINT
Calculated from SAT setpoint and reset signal. Displays
INACTIVE when in OFF Mode or not needing to be calculated.
FLUSHTMR
COOLING
FLUSHTMR
XX MIN
FLUSH
CYCLE ON
FLUSH TIMER AND FLUSH STATUS
Flush Timer screen will display if the unit is in Cooling Flush Mode,
Reheat Flush Mode, or Disabled. It will then display the time remaining
in minutes until the Flush Cycle begins. If the unit is in the Flush Cycle,
it will display FLUSH CYCLE ON.
NO
ALARMS
The alarms are as follows:
NO ALARMS: This will be shown if there are no current alarms.
SAT FAIL ERROR: The Supply Air Temperature sensor has been
disconnected for more than 60 seconds. This alarm will be disabled
when the sensor is reconnected.
COMM T/O ERROR: Communications have been lost with the
AAON unit controller. This alarm will disable when communications
resume.

17MHGRVX-B2 Module Technical Guide
LCD SCREENS
Setpoint and Force Valves Screens
Setpoint Screens
Refer to the following map when navigating through the Setpoint Screens.
From the SETPOINT Screen, press <ENTER> to scroll through the screens
and change setpoints. Use the <UP> and <DOWN> arrow keys to change
your selections. Then press <ENTER> to save the new setpoint.
WARNING: When the MHGRVX-B2 is operating in
Communications Mode (connected to the
AAON unit controller), these Setpoint
Screens will not appear on the LCD display
because they are controlled by the AAON
unit controller. To access these setpoints,
temporarily disconnect the MHGRVX-B2
from the AAON unit controller.
Minimum Default Maximum
40°F
5°C
70°F
21°C
150°F
65°C
SETPOINT
SAT SP
40-150ºF
REHEAT SUPPLY AIR TEMPERATURE SETPOINT
This is the target temperature while reheat is enabled. If you are using
the reset signal, this is the setpoint it will calculate to at zero volts. Will
display only in Stand-Alone Mode. The SAT Setpoint is set by the LCD
display in Stand-Alone Mode and is set by the AAON unit controller in
Communications Mode.
RESET SP
40-150°F
RESET REHEAT SUPPLY AIR SETPOINT
This is maximum temperature at which the Supply Air Temperature
will reset to. Will display only in Stand-Alone Mode.
The Reset SAT Setpoint is set by the LCD Display in Stand-Alone Mode
and is set by the AAON unit controller in communicating mode.
Force Valves Screens
Refer to the following map when navigating through the Force
Screens. From the FORCE VALVES screen, press <ENTER>. At
the FORCE MODE screen, press the <UP> arrow key to turn the
FORCE MODE on and press the <DOWN> arrow key to turn the
FORCE MODE o.
NOTE: When you turn the Force Mode o or after one hour
has elapsed, the valves will reinitialize to zero.
Minimum Default Maximum
40°F
5°C
70°F
21°C
150°F
65°C
FORCE
MENU
FORCE
MODE ON/OFF
Press the <UP> button to turn the Force Mode on. Press the <DOWN>
button to turn the Force Mode o󰀨.
FRC VALV
X%
FORCE VALVE PERCENTAGE
This screen only appears when Force Mode is on.
Press the <UP> button to increase the percentage. Press the <DOWN>
button to decrease the percentage.
FRC EXP
X%
FORCE EXPANSION VALVE PERCENTAGE
This screen only appears when Force Mode is on and Expansion
Valves are Enabled.
Press the <UP> button to increase the percentage. Press the
<DOWN> button to decrease the percentage.
FORCE
TIMEOUT
FORCE MODE TIME OUT
This screen will appear when the Force Mode times out after one hour.

18MHGRVX-B2 Module Technical Guide
LCD SCREENS
Protected Screens
Protected Screens Map
Refer to the following map when navigating through the LCD
Protected Screens. From the main screen, press the <ENTER> twice
until you get to the SOFTWARE Screen. Then hold the <UP> button
for ve seconds. To scroll through the rest of the screens, press the
<MENU> button.
MHGRVX
3005vXXX
S/A MODE,
SA MODE LOCKED
OR COMM MODE
SOFTWARE
3005vXXX
Hold for five seconds.
CONFIG
DIAGNSTC
ENTER TO
EXIT

19MHGRVX-B2 Module Technical Guide
LCD SCREENS
Protected Screens
Conguration Screens
Refer to the following map when navigating through the Conguration
Screens. From the CONFIG Screen, press <ENTER> to scroll through the
screens and change setpoints. Use the <UP> and <DOWN> arrow keys to
change your selections. Press <ENTER> to save any changes.
CONFIG
ADDRESS
1(132)
CURRENT ADDRESS OF THE BOARD.
The address is only used in Communications Mode. Default is 1.
AUX MODE
DISABLED
AUXILIARY MODE ENABLE
If enabled, auxiliary input controls the position of the valve.
AUX RELAY =
STANDARD
AUXILIARY RELAY
Standard or Reversing Valve
VLVSTEPS
2800
VALVE STEPS
This value cannot be modified.
TMPSCALE
FAHRENHT
TEMPERATURE SCALE
Fahrenheit (default) or Celsius
This setting is only used in Stand-Alone Mode.
S/A MODE
AUTODETECT
S/A MODE FORCED
S/A Mode Autodetect (default) or Locked.
Forces the module to be Stand-Alone Mode only.
EXP VLVS
DISABLED
REHEAT EXPANSION MODULE VALVES
Expansion Valves Disabled (default) or Enabled.
If Expansion Valves are enabled, the screen below will appear.
EXPFLUSH
SYNC
EXPANSION VALVES FLUSH
Expansion Valves flush independently or together. This screen is only
available if the Expansion Valves are enabled.
FLUSH CL
DISABLED
COOLING FLUSH CYCLE TIME
0-120 minutes or disabled.
FLUSH RH
DISABLED
REHEAT FLUSH CYCLE TIME
0-120 minutes or disabled.
FLSH@S/U
FLUSH AT STARTUP
Flush at startup, yes or no.

20MHGRVX-B2 Module Technical Guide
LCD SCREENS
Protected Screens
VALV RLY
VALVE RELAY
FLUSH, COMP2, or REHEAT
Configures how the VALVE relay operates.
VLV MAX
100
VALVE MAX
Used to configure the Max Reheat Valve %.
FLSH CND
DISABLED
FLUSH CONDENSER
Used to enable or disable condenser flushes.
Diagnostic Screens
Refer to the following map when navigating through the Diagnostic
Screens. From the DIAGNSTC Screen, press <ENTER> to scroll
through the screens.
DIAGNSTC
WDOG CNT
#
WATCH DOG TIMER
Displays the number of times the board has been reset due to
watchdog timer overflow.
PWER CNT
#
POWER LOSS COUNT
Displays the number of times the board has been
reset due to power loss.
STEP CNT
XXXX
STEP COUNT
Shows the step count status the valve is currently at.