Replace a PSC direct drive blower motor
If you’re in need of a PSC direct drive blower motor or just looking for a simple guide on how to replace one, cfm has you covered! We’ll be using the Evergreen motor in this example, so the same process won’t apply for a belt drive blower. We broke the process down into three segments, with a handful of sub segments to keep it simple
How to replace a PSC direct drive blower motor with an Evergreen motor:
The Evergreen motor is designed as a replacement motor for use on the following types of HVAC systems.
- PSC Direct Drive Blower Motors only (Not for use on Belt Drive Blowers)
- 115 or 230 VAC
- 1/5 HP thru 1 HP
- Residential and Light Commercial
- Split Systems and Packaged Units
- Clock-wise (CW) or Counter Clock-wise (CCW) rotation
- Make note of the current motor speed selections.
- If the Existing blower motor is operational –
- Record the Total External Static Pressure (TESP)
- Record the Temperature Difference across the unit in Heat Mode and/or Cool Mode
Installation of the Motor:
Motor Bracket and Mounting:
- The Evergreen motor requires a belly band style mounting bracket.
- The Evergreen motor is a NEMA 48 frame.
- This is the most common frame size for indoor blower motors.
- If the original motor has the same frame size, the original mounting bracket should work.
- If not, a new motor mount may be required.
- The belly band must fit the motor properly.
- It should be tight enough to prevent the motor from shifting on start-up
- Remove the blower assembly from the unit.
- Loosen the blower set screw.
- Remove the motor mount from the blower housing.
- Remove the motor from the motor mounting bracket.
- Position the new motor into the mounting bracket.
- Do not cover any motor vents with the bracket.
- Reassemble the motor mount to the blower housing with the new motor in place and the electrical connections facing down.
- Position the electrical connections between 4 and 8 o’clock.
- Center the blower in the blower housing.
- Position the blower set screw on the flat portion of the shaft, tighten securely.
- Replace the blower into the equipment.
- Evergreen electrical connections consist of three sets of motor leads –
- High Voltage Power Leads
- Connected directly to Line Power
- Powered at all times the unit is powered.
- High Voltage Communication Signal Leads
- Connected to the control terminals that previously operated the PSC Motor
- Low Voltage Communication Signal Leads
- Connected to the thermostat terminals of the control
- The motor comes with a yellow jumper installed in the electrical plug and a white jumper shipped with the motor.
- These jumpers are used to select the voltage in which the motor will be used.
- If the motor is being installed in a 230V application, leave the yellow jumper installed in the motor plug.
- If the motor is being used in a 115V application, remove the yellow jumper and replace it with the white jumper.
- High Voltage Power Wires:
- A Black Lead and a White Lead.
- Provide operating power to the motor.
- Connect the Black L1 wire of the Motor to Line Voltage
- L1 on 115VAC systems.
- L1 on 230VAC systems.
- Connect the White L2/N wire to L2 or N
- L2 on 230 VAC systems
- N on 115VAC systems
- Connect the Green w/Yellow stripe ground wire to any cabinet ground within reach.
- High Voltage Signal Wires:
- A Black Lead and a Red Lead.
- These leads determine the Horse Power selection and give the motor a run command.
- When high voltage appears on these signal leads, the motor will operate at its lowest speed at the predetermined Horse Power rating.
- Connected as follows:
- Red only with Black taped off
- Lowest Horse Power rating
- Black only with Red taped off
- Mid Horse Power rating
- Black and Red together
- Highest Horse Power rating
- Connect the lead(s) in parallel to all of the motor outputs from the control.
- IE, if the control wants the motor to operate for any reason – High Heat, Low Heat, High Cool, Low Cool, Fan Only, the signal lead(s) receive high voltage power.
- Identify the horse power rating of the original PSC motor.
- Use the chart in the installation instructions to determine which High Voltage communication connection(s) to use for the desired horsepower rating.
- Low Voltage Communication Signal Wires:
- These wires communicate to the motor that there is a call for Heat or Cool and the motor speed must be modified.
- High Speed
- Medium High Speed – (Available for ‘Y’ connection – See Diagram Below)
- Medium Low Speed
- Low Speed – (Available for ‘Y’ connection – See Diagram Below)
- Common (Low Voltage)
- Evergreen motor speed is selected by the low voltage inputs powered directly from the system thermostat terminals.
- The Low Voltage Communication Signal Wires are connected to the thermostat terminals on the control board.
- Unused Motor Communication Signal Wires are taped off and not used.
- Connect the Low Voltage Signal COMMON wire to the common thermostat terminal.
- Connect the desired speed(s) – Low Voltage signal wire(s) – to the appropriate HVAC System thermostat connection(s).
- Select Low Voltage Communication wires for speeds that best suit operation of the equipment.
- Select a heating speed that operates the equipment within the correct temperature rise for heating.
- Select a cooling speed that gives approximately 400 cfm per ton of cooling.
- If the same motor speed is required for both Heating and Cooling operation, you must use the ‘Y’ connection provided with the motor.
- Follow the installation instructions with the motor to apply it.
- Important Note:
- The ‘Y’ connection can only be used with the Orange or White Motor Leads
Labeling & Data Entry:
- Install the System ID Label on the HVAC system near the existing wiring diagram.
- Enter the Evergreen data.
- Record the Horse Power of the motor and the Date of Installation for future reference if needed.
Post-Installation of the Motor:
- Confirm airflow is matched to the systems performance requirements.
- Measure airflow with industry accepted instruments.
- Confirm the temperature rise on all fossil fuel heating systems to meet the OEM data plate specifications.
- Adjust the speed selections to achieve the design CFM per ton of cooling.
If you’d like to see an install guide for replacing a belt drive blower motor, leave us a comment below with some details of your project. You can also find Evergreen replacement motors & additional details via the cfm eStorefront.
Download the original service letter:
Evergreen-motor_Tech-Tips-TT-01-17_April-2017.pdf (252 downloads)