16
MHGRV-X Field Technical Guide
TROUBLESHOOTING
LED Diagnostics
General
The MHGRV-X 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 17
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 controller.
STATUS -
This green LED will light up and blink the board
address at startup. It will then blink according to what mode the
controller is in. See
Table 4, this page.
Only the highest priority
failure code will be shown. You must correct the highest priority
alarm before other problems will be indicated.
Diagnostic LEDs
ALARM -
This red LED will light up to indicate an alarm. The
type of alarm will display on the LCD display. The ALARM LED
also blinks when the expansion valve is initializing at startup.
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.
LED Troubleshooting
“POWER” LED -
When the MHGRV-X is powered up, the
POWER LED should light up and stay on continuously. 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.
“STAT” LED -
As previously described, when the board is first
powered up, the STAT LED will do the following:
• On for 10 seconds
• Blinks 30 times
• Blinks three times rapidly (after STEP LED is on for
45 seconds)
• Status code is repeatedly blinked every 10 seconds to
indicate controller status
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
