McQuay AGZ 035A, Installation, Operation And Maintenance Manual

Page: 51 / 96

IOMM AGZ-3 AGZ 035A through 065A 51
UNT Troubleshooting Chart
PROBLEM POSSIBLE CAUSES CORRECTIVE ACTIONS
Compressor will not
run
1. Main switch, circuit breakers open.
2. Fuse
blown.
3. Thermal overloads tripped or fuses blown.
4. Defective contactor or coil.
5. System shut down by protection devices.
6. No cooling required.
7. Liquid line solenoid will not open.
8. Motor electrical trouble.
9. Loose wiring.
1. Close switch.
2. Check electrical circuits and motor
winding for shorts or grounds. Possible
overloading. Replace fuse or reset
breakers after fault is corrected.
3. Overloads are auto reset. Check unit
closely when operating again.
4. Repair or replace.
5. Determine type and cause of shutdown
and correct it before resetting control.
6. None. Wait for load.
7. Repair or replace.
8. Check motor for opens, shorts circuit or
burnout.
9. Check all wire junctions. Tighten all
terminals.
High Discharge
Pressure
1. Dirty condenser coils.
2. Fan
not operating.
3. High Ambient conditions.
4. High return water temperature.
5. Overcharge
of refrigerant.
6. Non condensable.
7. Discharge valve partially closed.
1. Clean.
2. Check fan motor, contactor, contactor coil,
fan pressure switch. Repair or replace
defective part.
3. Check against design conditions.
4. Disable a compressor on each.
5. Remove excessive amount of charge.
6. Remove non condensable.
7. Back seat valve
Low Discharge
Pressure
1. Fan contactor failed in closed position.
2. Fan pressure switch defective.
3. Low
ambient temps.
4. Low on refrigerant charge.
5. Reduced chilled water flow.
6. No load and on hot gas bypass.
1. Repair or replace.
2. Replace pressure switch.
3. Install
SpeedTrol Kit.
4. Add refrigerant.
5. Check flow and correct.
6. Adjust hot gas bypass to maintain a higher
evaporator pressure.
High Suction
Pressure
1. Excessive load (high return water temp).
2. Controller not staging up.
3. Compressor capacity reduced.
4. Can be associated with high condenser pressure. 1. Check water flow, reduce load.
2. Check UNT controller. Replace if
defective.
3. Replace compressor.
4. Check reasons for high condenser
pressure.
Low Suction
Pressure
1. Low refrigerant charge.
2. Defective expansion valve.
3. Dirty
filter drier.
4. Reduced water flow.
5. Hot gas bypass valve not set properly.
6. Liquid line solenoid valve not opening.
7. UNT controller defective.
8. Gasket failure in evaporator head ring.
1. Add refrigerant.
2. Check operation. Repair or replace.
3. Replace
cores.
4. Increase water to design GPM.
5. Set valve for a higher pressure.
6. Repair or replace.
7. Check water sensor, set point dial, control
band dial. Calibrate, repair or replace.
8. Replace gasket.
Compressor Oil Loss
1. Excessive refrigerant flood back.
2. Defective crankcase heater.
3. Low
refrigerant charge.
4. Hot gas bypass not set properly.
1. Check TXV. Repair or replace.
2. Replace
heater.
3. Add refrigerant.
4. Increase hot gas flow.
Compressor
Overloads or Circuit
Breakers Open
1. Low line voltage.
2. High compressor amps.
3. Loose power wiring.
4. High condenser pressures.
5. Single
phasing.
1. Check incoming voltage. Report to
electrical supplier.
2. Determine cause and correct.
3. Tighten all connections.
4. Refer to High Condenser Pressure.
5. Replace fuses or breaker.
Compressor Internal
Motor Switch Open
1. Compressor amps high.
2. Motor winding damaged.
1. Refer to the above concerning high
compressor amps.
2. Check motor winding resistance. Replace
if defective.
Freeze Protection
Trips
1. Pressure transducers defective.
2. Low water flow.
3. Low loads / erratic water flow.
4. Controller stage timing.
5. Defective TXV.
6. Hot gas bypass not set properly.
7. Low ambient operation.
1. Compare output to actual refrigerant
pressures.
2. Check water GPM and correct.
3. Check pump operation, water strainer, air
handler control valves.
4. Check timing and reset as necessary.
5. Check and repair or replace.
6. Set hot gas bypass.
7. Install SpeedTrol, wind baffles.
Erratic Loading and
Unloading
1. Chilled water flow erratic.
2. System load erratic.
3. Bad water sensor.
4. Reset function calibration.
5. Defective UNT controller. 1. Check for reasons and correct.
2. Check water flow control valve operation.
3. Replace.
4. Re-calibrate
5. Replace