McQuay MWM Service Manual page 66

MCQUAY Service Guide Book
Rooftop Panel
Alarm Shown On The Rooftop Panel
• Whenever panel received a new alarm, an alarm message will pop up on the LCD. It shows type of alarm,
alarm occurred time and date. Backlight blinking (if Backlight is not OFF) and alarms buzzer produces
beeping sound (if it's set ON). The buzzer will beep for 10 minutes after that stop for 5 minutes (with the
Backlight still blinking), this process keep looping until the alarm is dissolved or a key press is detected.
• Backlight will stop blinking via key press. Press UP or DOWN key to scroll the alarms display if more than
one alarms occurred. Press ESC to exit to the summary pages.
• If one of the alarms has been dissolved, pop up message will update its display (would not show the
dissolved alarm anymore). If all the alarms have been dissolved, it will exit to the summary pages
automatically.
• If the existing alarm has not been dissolved and another new alarm is occurred, the pop up message will
update to the latest alarm.
• A sign [A] will be shown and blink in Summary Pages as long as the alarm has not been dissolved. If user
needs to view current existing alarms, press "ALARM" key in the summary pages or go to ALARM MENU in
MAIN MENU.
• The panel can display up to 20 new alarms at once (which are not dissolve yet).
• All the incoming new alarms record will be store in ALARM MENU – Show Alarms.
• The alarm histories are viewable ONLY when all the new alarm already dissolved.
• If the contact type alarm is set to manual reset, the alarm can only be dissolved by off and on BACK
rooftop unit.
Error Message
1. MB & economizer
communication fail
2. Memory Error
3. Economizer Error
4. ESD contact open
5. Compressor 1 / 2
overload
6. Compressor 1 / 2 low
pressure trip
7. Compressor 1 / 2 high
pressure trip
8. Compressor 1 / 2
discharge overheat
Possible causes
Communication wires not
connected
External noise / interference
Main PCB / Economizer PCB
faulty
EEPROM data corrupted
Refer to the economizer board
error code table.
Normally close ESD contact
become open
Insufficient airflow / Air short
circuit
Heat exchanger dirty
Refrigerant overcharge /
undercharge
Condenser fan motor faulty
EXV or EXV PCB defective
Compressor malfunction
Main PCB faulty
Refrigerant undercharge
Pressure switch faulty
Main PCB faulty
Insufficient airflow / Air short
circuit
Heat exchanger dirty
Condenser fan motor faulty
Refrigerant overcharge
EXV or EXV PCB faulty
High Pressure switch faulty
Main PCB faulty
Discharge sensor malfunction
Insufficient airflow / Air short
circuit
Heat exchanger dirty
Action
Connect correctly and operate again.
Avoid from noise source / add ferrite core.
Replace main PCB / economizer PCB.
Replace main PCB and operate again.
Refer to the economizer board error code
table.
ESD contact shorted with wired. If fail,
replace main board and operate again.
Ensure no obstacle around the unit.
Ensure no dirt or dust on filter and coil.
Recharging with correct amount of
refrigerant.
Replace fan motor.
Replace EXV or EXV PCB.
Replace compressor.
Replace main PCB.
Top up with correct amount of refrigerant.
Replace pressure switch.
Replace main PCB.
Ensure no obstacle around the unit.
Ensure no dirt or dust on filter and coil.
Replace fan motor.
Recharging with correct amount of
refrigerant.
Replace EXV or EXV PCB.
Replace pressure switch.
Replace main PCB.
Replace new discharge sensor.
Ensure no obstacle around the unit.
Ensure no dirt or dust on filter and coil.
65
Diagnosis