Greenheck MPX (472695) - Manual (Page 29)

Troubleshooting - Unit
Symptom Possible Cause Corrective Action
Blower fails
to operate
Blown fuse or open circuit breaker. Replace fuse or reset circuit breaker and check amps.
Defective motor or capacitor. Replace.
Motor starter overloaded. Reset starter and check amps.
Electrical
Check for On/Off switches. Check for correct supply
voltage. Check Control wiring.
Drive Check for broken or loose belts. Tighten loose pulleys.
Motor
starters
“chatter” or
do not pull in
Control power (24 VAC) wiring run is
too long. (Resistance should not
exceed 0.75 ohms).
Shorten wiring run to mechanical room or install a relay
to turn unit on/off. Consult factory for relay information.
Increase wire gauge size so that resistance is 0.75
ohms or less.
Incoming supply power is less than
anticipated. Voltage supplied to starter
coil must be within +10% / -15% of
nominal voltage stated on the coil.
Need to increase supply power or use a special control
transformer which is sized for the actual supply power.
Motor over
amps
CFM too high. Check rpm and adjust drives if needed.
Static pressures are higher than design. Check for dirty filters. Improve ductwork.
Motor voltage incorrect.
Check motor wiring. Check motor nameplate versus
supplied voltage.
Motor horsepower too low.
See specifications and catalog for fan curves to
determine if horsepower is sufficient.
Shorted windings in motor. Replace motor.
Low airflow
(cfm)
Unit damper not fully open. Adjust damper linkage or replace damper motor.
System static pressure too high.
Improve ductwork to eliminate losses using good duct
practices.
Blower speed too low. Check for correct drives and RPM with catalog data.
Fan wheels are operating backwards.
For 3-phase, see Direction of Fan Wheel Rotation in
Unit Start-Up section.
Dirty filter.
Replace filters or follow cleaning procedures in Routine
Maintenance section of this manual.
Leaks in ductwork. Repair.
Elbows or other obstructions may be
obstructing fan outlet.
Correct or improve ductwork.
Belt slippage. Adjust belt tension.
High airflow
(cfm)
Blower fan speed too high.
Check for correct fan RPM. Decrease fan speed if
necessary.
Filter(s) not in place. Install filters.
Insufficient static pressure (Ps).
(airflow resistance)
Induce Ps into system ductwork. Make sure grilles
and access doors are installed. Decrease fan speed if
necessary.
Always have a completed Pre Start-Up Checklist, Unit Start-Up Checklist and Optional Accessories Checklist prior to
requesting parts or service information.
29 Model MPX Make-Up Air Unit
®