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What steps should be followed when replacing a motor in my system?
What steps should be followed when replacing a motor in my system?
When replacing a fan or blower motor in the HVAC/R system there are a few steps that should be followed.
Old Motor
1. First and foremost, protect yourself from any electrical hazards. Check to see if any fault codes are available that might help in troubleshooting, then disconnect power to the system. Lock out and tag the power supply so that others recognize that the power is off intentionally, reducing the risk of accidental reconnection. Then, using your multimeter, double and triple check to make certain that there is no power to the system.
Lock Out and Tag
2. If the motor is equipped with a capacitor, discharge the capacitor using a 15,000 Ohm, 2-Watt bleed resistor. If the motor is an ECM, do not access the control section of the motor for at least 5 minutes after power was last applied.
Bleed Resistor
3. In the case of a direct drive motor, measure where the blower wheel/impeller is positioned in the blower housing or where the fan blade is positioned in the orifice. It’s important that they are in the same position when the new motor is installed. Check the blower wheel/impeller or fan blade for wear and balance. Replace if necessary. With a belt drive motor, check the belt and pulley for wear. Replace if necessary. Check mounting brackets and rubber grommets for wear and replace if necessary.
Positioning Fan Blade in Orifice
4. Disconnect and remove old motor, capacitor, hardware, pulley, blower wheel/impeller, fan blade, and connectors as appropriate. Even if the old capacitor is OK, a new capacitor that matches the specifications of the new motor should be used. Note where the leads are oriented so that the new motor can be installed in the proper orientation. Mark the rotation of the motor so that the new motor operates in the same rotation.
5. Clean the coils, blower, blower wheel/impeller, condenser, fan blade, and other areas around the motor.
New Motor
1. Turn the shaft by hand to make certain that the motor rotates freely. If the new motor is an ECM, it’s possible that the shaft might seem to “catch” when turning it by hand. This is normal with a permanent magnet motor like an ECM.
2. Make any electrical connection changes for voltage and rotation. Note that with some ECMs, they will automatically sense their proper rotation the first time that they are energized. They will then operate in that rotation thereafter. Cap-off or tape any speed taps that will not be used so that they will be insulated, preventing an accidental short circuit. If needed, attach quick connects to the motor leads.
3. For totally enclosed condenser fan motors, make certain that the drain plug on the “down” side of the motor is removed so that condensation can drain from the “weep hole”. ECMs should be mounted in such a way that their connectors are as close to the down position as possible.
Remove Drain Plug from “Down” Side of Motor
4. Install motor in mounting bracket. Do not block vent holes in motor with bracket. Position a belly band towards the center of the motor where there is more support. If rubber grommets are used with the belly band, be certain that they are properly installed and are not cracked or broken. When included, use the metal ferrules or sleeves provided with the rubber grommets. An ECM can be very sensitive to poor mounting and may not operate properly if the belly band or its components are damaged. On a resilient base mounted motor, the resilient rings should be centered in the mounting bracket. If using the bracket from the old motor, be certain that form, fit, and function is suitable. Be cautious that leads from the motor do not get pinched by the mounting bracket when installing. Be certain that the motor and mounting assembly is secure to the device when installed.
5. Assure that the motor is grounded properly. This is more than the ground wire from the motor being attached to a non-painted metal part of the equipment. This means that there should only be one common ground per system and that the maximum ground resistance should be 25 Ohms. The optimum ground would measure 5 Ohms or less. Not only is a poor ground a safety issue, but it can also be the cause of improper operation.
6. Connect the power leads to the source of power in the device. This could be a contactor, relay, terminal board, or perhaps some other device. REMEMBER, POWER REMAINS DISCONNECTED FOR THIS STEP! Connect the speed taps to the control board or other appropriate device. Connect the capacitor leads from the motor to the capacitor.
7. Attach the blower wheel/impeller, fan blade, or pulley, using shaft keys where appropriate and securely tightening to the motor shaft, making certain that they are positioned and aligned properly in the device. If a belt drive application, be certain that the pulley is adjusted correctly and that the proper belt tension is achieved. A belt tensioning device should be used for this. Do not force the blower wheel/impeller, fan blade, or pulley onto the motor shaft. Doing so could result in bearing damage, misalignment, damage to the blower wheel/impeller, fan, pulley, noise issues, vibration, and more.
8. Spin the motor shaft to make certain that it is continuing to spin freely and that nothing is interfering with rotation.
9. Remove the lock out device from the power source and reapply power. Check to see that the proper voltage is being supplied to the motor. This includes both high voltage and low voltage.
10. With all doors, panels, guards, filters, ducts, coils, and other components of the system in place, operate the system and the motor through its speeds and cycles. All components must be in place to properly load the motor. When everything is in place, operate the motor and check the full load amps (FLA). If all of the components are not in place, the FLA reading will not be representative of true FLA. The most common way of measuring Amps is to use the clamp on an ammeter or multimeter. Place the clamp over one of the power leads of the motor while the motor is operating under load. The amps measured on the meter represent FLA. A rule of thumb with direct drive blower and fan motors used in HVAC/R, the FLA should not be more than 10% higher or more than 25% lower than motor nameplate amps. Belt drive motors should not exceed their service factor (SF) Amps shown on the motor nameplate. It may be difficult to measure motor amps when all components are in place in that the motor may be inaccessible. If this is the case, it may be necessary to attach jumper wires to the motor leads or use a blue tooth multimeter. With a Bluetooth multimeter, the meter can be attached to the leads inside the equipment, and by pairing a smart phone, the readings will be captured on the phone.
11. Check for any unusual sounds, proper air flow, and temperature changes.
12. If all checks well, clean up the work area, gather your tools, and feel confident about having another great installation. Mission accomplished!
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