Troubleshooting a Blower Motor Dropping Out on the MRCOOL Universal Split Series Air Handler

If you're experiencing issues with the blower motor on your MRCOOL Universal Split System air handler intermittently dropping out, there are several key areas to check. Here's a step-by-step guide to troubleshooting the problem.

1. Check Incoming Power

Start by testing the power supply to the air handler. Using a voltmeter set to AC voltage, check the voltage between terminals L1 and L2. Ensure the incoming voltage is below 253V. Anything higher can cause operational issues and may indicate a problem with the home's power supply.

2. Check Low Voltage Connections

Next, check the low voltage connections while the system is calling for operation:

• R to C terminals: Use your voltmeter to verify that you're getting at least 24V or higher between the R and C terminals.
• G to C terminals: Similarly, check the G to C terminals to ensure you're reading 24V. If the voltage is below 24V or doesn't register at all, this may indicate a short in the thermostat wiring or an issue with the thermostat itself. Inspect the wiring and thermostat to correct any problems.

3. Check Static Pressure in the Ductwork

If the low voltage readings are within range, it's time to check the static pressure in the ductwork using a manometer. High static pressure can cause the blower motor to overwork, leading to overheating and intermittent dropout.

• The static pressure should stay around 0.8 IN.W.C or lower, with an ideal reading of around 0.6 IN.W.C.
• Common causes of high static pressure include:
  • Air filters with a high MERV rating that restrict airflow.
  • Dirty air filters, which need to be cleaned or replaced.
  • A dirty A-coil or blower wheel, both of which should be cleaned.
  • Ductwork that is too tight, restricting airflow.
  • Zoning systems without a properly sized bypass duct to redirect excess airflow back to the return duct.

4. Inspect the Blower Motor

If all of the above checks are within range and the blower motor is still dropping out, the issue may lie with the blower motor itself. In this case, the motor may need to be replaced.

By following these steps, you can identify the root cause of the blower motor issue and take corrective action to restore proper function to your MRCOOL Universal Split System air handler.