TL;DR
A Greenheck CUE fan motor overheating typically means the system resistance is higher than expected, or the motor cooling fins are blocked. Measure current against the motor nameplate FLA and inspect the air path around the motor housing.
What you might see
- motor housing above 85 degrees Celsius
- overload relay trips repeatedly
- motor current above nameplate FLA
- fan discharge static pressure higher than design
Likely causes
Fan operating against higher system resistance than design, drawing excess current
Motor cooling fins clogged with lint, dust, or debris reducing heat dissipation
Overload relay set below the motor nameplate FLA
Ambient temperature in the mechanical room above the motor's rated temperature class
Required tools
- Clamp ammeter (true-RMS)
- Manometer or magnehelic gauge
- IR thermometer
- Cleaning brush
- Arc-flash PPE
- LOTO kit
Safety first
- Current measurements on the motor disconnect require energized work PPE and an energized work permit.
- Do not repeatedly reset an overload relay that keeps tripping without investigating the root cause. Repeated resets cause winding heat buildup and premature motor failure.
Procedure
- 1
Clamp an ammeter on all three motor legs and record current at steady state. Compare to the nameplate FLA.
Warning: Current measurement requires opening the motor disconnect panel while energized. Use arc-flash PPE and category-rated probes. - 2
If current is above FLA, measure the fan discharge static pressure with a manometer and compare to the design value. Higher than design means the system is more restrictive.
- 3
Inspect all ductwork filters, coils, and discharge louvres for blockage. Clean or replace any blocked filter.
- 4
Lock out the fan motor and inspect the motor cooling fins and intake screen for debris. Clean with a brush. Do not blow compressed air directly into the winding end-bells.[1]
- 5
Verify the overload relay is set to the motor nameplate FLA. An undersize setting causes nuisance trips even at normal current.[1]
- 6
If current is near FLA but the system resistance is at design, check the ambient temperature around the motor. Install a ventilated enclosure or add supplemental cooling if ambient exceeds the motor's ambient temperature rating.
- 7
If current is significantly above FLA and system resistance is at design, the sheave ratio may have been changed to a higher RPM, causing the motor to operate above its design point. Consult the original fan schedule.
Sources
Greenheck CUE Centrifugal Upblast Roof Exhaust Fan Installation and Maintenance Manual, Greenheck Fan Corporation
Greenheck CUE Utility Fan installation, operation and maintenance instructions, motor current, overload setting, and maintenance (general)
View source
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