TL;DR
A squeal from a Greenheck CUE fan is typically a slipping belt. A grinding or rumble is a bearing. Check belt tension first as it is quickest, then inspect the bearings.
What you might see
- high-pitched squeal under load
- grinding or rumbling noise at running speed
- noise changes when belt tension is adjusted
- belt shows glazing or cracking on the inner surface
Likely causes
Belt slipping on the sheave due to insufficient tension or a worn/glazed belt
Worn drive-end or idler bearing generating broadband or tonal noise
Sheave misalignment causing belt to run at an angle and squeal
Aerodynamic stall from operating far off the design point on the fan curve
Required tools
- Belt tension gauge or spring scale
- Straightedge or string line for sheave alignment
- IR thermometer for bearing temperature check
- Replacement belt (correct Gates, Browning, or OEM part number)
- LOTO kit
Safety first
- Never attempt to check or adjust belt tension while the fan is running. The pinch point between the belt and sheave can pull a hand into the drive.
- Apply LOTO and verify zero rotation before opening the belt guard.
Procedure
- 1
Lock out the fan disconnect.
Warning: Belt drives store energy and can release it suddenly. Confirm LOTO before inspecting belts or sheaves. - 2
Inspect the belt for glazing, cracking, or fraying. A glazed belt has a hard, shiny inner surface and will slip under load even with correct tension.
- 3
Check belt tension using the deflection method: apply a perpendicular force of the manufacturer-specified load to the belt midspan and measure deflection. The deflection should match the value in the Greenheck fan manual for the sheave span.[1]
- 4
If tension is low, adjust the motor mounting position to add tension. Snug the jam nuts on the tensioning screw after adjustment.[1]
- 5
Check sheave alignment by laying a straightedge across the two sheave faces. They should be coplanar within 0.06 inches per foot of sheave center distance.
- 6
Inspect both bearings by rotating the fan shaft by hand while listening and feeling for roughness or resistance. Elevated temperature at the bearing housing (above 85 degrees Celsius) with no other cause indicates a failing bearing.
- 7
Replace any worn or glazed belt and any bearing showing roughness. Replace bearings in pairs.
Sources
Greenheck CUE Centrifugal Upblast Roof Exhaust Fan Installation and Maintenance Manual, Greenheck Fan Corporation
Greenheck CUE Utility Fan installation, operation and maintenance instructions, belt tension and bearing inspection procedures (general)
View source
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A slipping belt loses fan speed and generates heat at the sheave. Check belt condition, tension, and sheave groove wear. A glazed or cracked belt must be replaced, not just re-tensioned.
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