Troubleshooting - McQuay MDB075B Manual

8. Sequential Control For Cool Mode
The starting sequence for indoor fan, outdoor fan and compressors is shown as below:
2 seconds
Start
15 seconds
15 seconds
15 seconds
15 seconds
* if available and applicable
The compressors will be turned on one by one depending on the on/off conditions shown in the above
9. Sequential control for heat mode
The starting sequence for indoor fan, outdoor fan and compressors is as shown below :
2 seconds
Start Indoor fan
15 seconds
outdoor fan 1
15 seconds
outdoor fan 2
15 seconds
outdoor fan 3
15 seconds
outdoor fan 4
* if available and applicable
The compressors will be turned on one by one depending on the on/off conditions shown in the above.

Troubleshooting

When any air conditioner malfunction is noted, immediately switch off the power supply to the unit and
contact the local dealer, if necessary. Some simple trouble shooting tips are given below :
Trouble
1. Fan does not work
2. Fan works, but
compressor does
not work
3. Both fan and
compressor does
not work
4. Air-conditioner
works but cooling
not satisfactory
Indoor fan
2 seconds
outdoor fan 1
2 seconds
outdoor fan 2
2 seconds
outdoor fan 3
2 seconds
outdoor fan 4
2 seconds
all 4 way valves
2 seconds
compressor 1*
2 seconds
compressor 2*
2 seconds
compressor 3*
2 seconds
compressor 4*
Probable Cause
1. No power supply
2. Fan capacitor faulty
3. Fan motor faulty
4. Switch faulty
1. Thermostat setting too high
2. Dual pressure control trip
3. Compressor faulty
4. Compressor contactor faulty
1. Power failure
2. Starter trip
3. Fuse blown in power switch or operating
unit
1. Thermostat setting too high
2. Doors and/or windows not closed
3. Condenser coil dirty
4. Some objects blocking the inlet and/or
outlet of the unit
5. Insufficient refrigerant charge.
compressor 1*
compressor 2*
compressor 3*
compressor 4*
15 seconds
Heater 1*
1. Check power supply
2. Contact local dealer
3. Contact local dealer
4. Change switch
1. Reset thermostat
2. Reset Pressure Control
3. Contact local dealer
4. Contact local dealer
1. Operate when power supply resume
2. Reset starter
3. Check and replace fuse
1. Reset thermostat
2. Close doors and/or windows
3. Contact local dealer
4. Remove the object
5. Contact local dealer
101
15 seconds
Heater 2*
Suggested Action