Troubleshooting

IMPELLER HITTING INLET OR HOUSING

a. Impeller not centered in inlet or housing.
b. Inlet or housing damage.
c. Crooked or damaged impeller.
d. Shaft loose in bearing.
e. Impeller loose on shaft.
f. Bearing loose in bearing support.
g. Bent shaft.
h. Misaligned shaft and bearings.

IMPELLER HITTING CUTOFF

a. Cutoff not secure in housing.
b. Cutoff damaged.
c. Cutoff improperly positioned.

DRIVE

a. Sheave not tight on shaft (motor or fan).
b. Belts hitting belt tube.
c. Belts too loose. Adjust for belt stretching after 48 hours operating.
d. Belts too tight.
e. Belts wrong cross-section.
f. Belts not ‘matched’ in length on multi-belt drive.
g. Variable pitch sheaves not adjusted so each groove has same pitch diameter (muiti-belt drive).
h. Misaligned sheaves.
i. Belts worn.
j. Motor, motor base or fan not securely anchored.
k. Belts oily or dirty.
l. Improper drive selection.
m. Loose key.

COUPLING

a. Coupling unbalanced. misaligned, loose or may need lubricant.
b. Loose key.

BEARING

a. Defective bearing.
b. Needs lubrication.
c. Loose on bearing support.
d. Loose on shaft.
e. Seals misaligned.
f. Foreign material inside bearing.
g. Worn bearing.
h. Fretting corrosion between inner race and shaft.
I. Bearing not sitting on flat surface.

SHAFT SEAL SQUEAL

a. Needs lubrication.
b. Misaligned.
c. Bent shaft.
d. Bearing loose on support.

IMPELLER

a. Loose on shaft.
b. Defective impeller. Do not run fast. Contact the manufacturer.
c. Unbalance.
d. Coating loose.
e. Worn as result of abrasive or corrosive material moving through flow passages.
f. Blades rotating close to structural member.
g. Blades coinciding with an equal number of structural members.

HOUSING

a. Foreign material in housing.
b. Cutoff or other part loose (rattling during operation).

MOTOR

a. Lead-in cable not secure.
b. AC hum in motor or relay.
c. Starting relay chatter.
d. Noisy motor bearings.
e. Single phasing a 3 phase motor.
f. Low voltage.
g. Cooling fan striking shroud.

SHAFT

a. Bent
b. Undersized. May cause noise at impeller, bearings or sheave.

HIGH AIR VELOCITY

a. Ductwork too small for application.
b. Fan selection too large for application.
c. Registers or grilles too small for application.
d. Heating or cooling coil with insufficient face area for application.

OBSTRUCTION IN HIGH VELOCITY GAS STREAM MAY CAUSE RATTLE, OR PURE TONE WHISTLE

a. Dampers.
b. Registers.
c. Grilles.
d. Sharp elbows.
e. Sudden expansion in ductwork.
f. Sudden contraction in ductwork.
g. Turning vanes.

PULSATION OR SURGE

a. Restricted system causes fan to operate left of peak.
b. Fan too large for application.
c. Ducts vibrate at same frequency as fan pulsation.
d. Rotating stall.
e. Inlet vortex surge.
f. Distorted inlet flow

GAS VELOCITY THROUGH CRACKS, HOLES OR PAST OBSTRUCTIONS

a. Leaks in Ductwork.
b. Fins on Coils.
c. Registers or Grills.

RATTLES AND/OR RUMBLES

a. Vibrating Ductwork.
b. Vibrating cabinet parts.
a. Vibrating parts not isolated from building

FAN

a. Impeller installed backwards.
b. Impeller running backwards.
c. Improper blade angle setting.
d. Cutoff missing or improperly installed.
e. Impeller not centred with inlet collar(s).
f. Fan speed too slow.
g. Impeller/inlet dirty or clogged.
h. Improper running clearance.
i. Improper inlet cone to wheel fit.
j. Improper set inlet vane or damper.

DUCT SYSTEM

a. Actual system is more restrictive (more resistance to flow) than expected.
b. Dampers closed.
c. Registers closed.
d. Leaks in supply ducts.
e. Insulating duct liner loose.

FILTERS

a. Dirty or clogged.
b. Replacement filter with greater than specified pressure drop.

COILS

a. Dirty or clogged.
b. Incorrect fin spacing.

RECIRCULATION

a. Internal cabinet leaks in bulkhead separating fan outlet (pressure zone) from fan inlets (suction zone).
b. Leaks around fan outlet at connection through cabinet bulkhead.

OBSTRUCTED FAN INLETS

a. Elbows, cabinet walls or other obstructions restrict air flow. Inlet obstructions cause more restrictive systems but do not cause increased negative pressure readings near the fan inlet(s). Fan speed may be increased to counteract the effect of restricted fan inlet(s). CAUTION! Do not increase fan speeds beyond the manufacturer’s recommendations.

NO STRAIGHT DUCT AT FAN OUTLET

a. Fans which are normally used in duct systems are tested with a length of straight duct at the fan outlet. If there is no straight duct at the fan outlet, decreased performance may result. If it is not practical to install a straight section of duct at the fan outlet, the fan speed may be increased to overcome this pressure loss. CAUTION! Do not increase fan speeds beyond the manufacturer’s recommendations.

OBSTRUCTION IN HIGH VELOCITY AIR STREAM

a. Obstruction near fan outlet or inlet.
b. Sharp elbows near fan outlet or inlet.
c. Improperly designed turning vanes.
d. Projections, dampers or other obstruction in a part of the system where air velocity is high.

SYSTEM

a. Oversized ductwork.
b. Access door open.
c. Registers or grilles not installed.
d. Dampers set to by-pass coils.
e. Filter(s) not in place.
f. System resistance low.

FAN

a. Fan speed too fast.
b. Improper blade angle setting.