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MHGRVX-A2 Module Technical Guide
TROUBLESHOOTING
LED Diagnostics
General
The MHGRVX-A2 is equipped with LEDs that can be used to
verify operation and perform troubleshooting. There are LEDs
for communication, operation modes, and diagnostic codes. The
module has 14 LEDs—12 used for operation and status, and two
used for alarms.
See
Figure 5, page 22
for the LED locations. The LEDs associated
with these inputs and outputs allow you to see what is active without
using a voltmeter. The LEDs and their uses are as follows:
Operation LEDs
POWER -
This green LED will light up to indicate that 24 VAC
power has been applied to the module. If it does not light up,
check to be sure that the power wiring is connected to the board,
the connections are tight, and the transformer is powered. If after
making all these checks, the POWER LED does not light up, the
board is probably defective.
STATUS -
At power up the Status light blinks three quick blinks
five times with a pause after the third blink. Then, the CONDENSER
VALVE DRIVE LED starts blinking as the condenser valve is sent
to 100% and reheat valve is sent to 0%. After this, the STATUS
LED blinks according to what mode the module is in. See
Table
4, this page
.
Diagnostic LEDs
ALARM (on board) -
This red LED will light up to indicate an
alarm. The type of alarm will display on the LCD display. See
Table 5, this page.
ALARM (above LCD display) -
The LED blinks when an alarm
is active.
Communication LED
COMM -
This yellow LED will light up and blink when
communications are detected.
Relay LEDs
FAN -
This green LED will light up to indicate that the relay for the
“FAN” output is energized and its Normally Open Contact is closed.
COMP -
This green LED will light up to indicate that the relay for
the “COMP” output is energized and its Normally Open Contact
is closed.
VALVE -
This green LED will light up to indicate that the relay for
the “VALVE” output is energized and its Normally Open Contact
is closed.
AUX -
This green LED will light up to indicate that the relay for the
“AUX” output is energized and its Normally Open Contact is closed.
Binary Input LEDs
REHEAT ENABLE -
This green LED will light up when the
Reheat is enabled.
HEAT OVERRIDE -
This green LED will light up when Heat
Override is enabled.
COOL OVERRIDE -
This green LED will light up when Cool
Override is enabled.
Analog Output LEDs
CONDENSER VALVE DRIVE -
This LED blinks any time the
condenser valve is opening and reheat valve is closing.
REHEAT VALVE DRIVE -
This LED blinks any time the reheat
valve is opening and the condenser valve is closing.
No. of Blinks
STATUS LED
1
Off Mode
2
Reheat Mode
3
Flush Mode
4
Force Mode
5
SAT Sensor Failure Mode
Table 4: STATUS LED Blink Codes
No. of Blinks
ALARM LED
1
Supply Air Temperature Sensor Failure
2
Communications Time Out Error
Table 5: ALARM LED Blink Codes