Orion System MHGRV III - Manual (Page 16)

MHGRV III Controller Technical Guide
Operator Interface 16
Using LEDs to Verify Operation
The MHGRV III controller is equipped with LEDs that can be used as
very powerful troubleshooting tools. The MHGRV III controller board
has six LEDs. Two of these LEDs are used in troubleshooting. See Figure
6 for the LED locations. The LEDs and their uses are as follows:
LED Descriptions
“STAT” - This is the diagnostic blink code LED. It will light up and
blink out diagnostic codes. See Table 2 for blink codes.
“STEP” - This LED is on any time the modulating hot gas reheat valve
is moving.
“POWER” - This LED will light up to indicate that 24 VAC power has
been applied to the controller.
“FAN” - This light indicates that the relay for the “FAN” output is
energized and its Normally Open Contact is closed.
“CMP” - This light indicates that the relay for the “CMP” output is
energized and its Normally Open Contact is closed.
“VALVE” - This light indicates that the relay for the “VALVE” output
is energized and its Normally Open Contact is closed.
“AUX” - This light indicates that the relay for the “AUX” output is
energized and its Normally Open Contact is closed.
Figure 6: LED Locations
LED Diagnostics
“POWER” LED: When the MHGRV III Controller 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 fi rst powered
up, the STAT LED will do the following:

On for 10 seconds

Blinks 30 times

Blinks 3 times rapidly (after STEP LED is on
for 45 seconds)

Status code is repeatedly blinked every ten seconds to
indicate controller status
Priority No. of Blinks Status
Lowest 1 Normal Operation
- 2 SAT Over High Limit (170º)
- 3 Bad SAT Sensor
Highest 4 Force Mode Active
Table 2: STAT LED Blink Codes
Only the highest priority failure code will be shown. You must correct
the highest priority alarm before other problems will be indicated.
Other Checks
Supply Air Temperature Sensor
If you suspect the Supply Air Temperature Sensor is not reading cor-
rectly, make sure the wiring terminal connections are tight and that any
wiring splices are properly connected. You can check the operation of the
Supply Air Temperature Sensor by measuring the resistance or voltage
using a digital multimeter. Set the meter to DC Volts. Place the positive
probe on the AIN terminal and the negative probe on the GND terminal.
Read the DC Volts and fi nd that voltage in Table 3.
Read the temperature corresponding with that voltage and determine
if this is close to the actual temperature the sensor is exposed to. If the
temperature from the chart is different by more than a few degrees, you
probably have a defective or damaged sensor. You can also check the
sensor resistance to determine correct operation. To read the resistance,
set the meter to Ohms. Unplug the sensor connector from the board and
measure the resistance across the disconnected wires. This resistance
should match the corresponding temperature from Table 3.
Troubleshooting