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Furnace Motor Diagnostics: 4 Ways to Prepare for The Cold Months Ahead

furnace motorWinter is on its way — you can almost feel it in the fall air. It’s the time that Minnesotans start thinking about the cold months ahead and begin making sure they’re ready for a comfortable, maintenance-free heating season. Planning ahead should include an annual inspection — always a good idea to make sure everything is in tip-top shape.

But beyond a general check-up, there are some more in-depth diagnostics to consider. And one really important one is the condition of your furnace motor. No one wants to get caught with a failed motor — or one that is working at sub-par efficiency — in the middle of a Minnesota winter.

The Job Your Motor Performs

Your furnace motor is really the workhorse of your HVAC system. It’s what draws heat from your furnace and distributes it throughout your home. Yet its importance is often overlooked by homeowners. That’s because most motors run pretty quietly, don’t need a lot of maintenance, and often run for years on end. That doesn’t mean they never need tending to. Especially if you’re a DIYer, there are some preventative measures and inspections that can help keep your motor running smoothly and efficiently.

Keep the Motor Clean

The best preventative maintenance you can do on your motor is to keep it clean. Since furnace motors are usually located in the basement or in a laundry area, it’s easy for lint and debris to get stirred up and block the motor holes.

Keep the area around the motor as clean as you can, make sure to change your filters often (as much as once a month during the heating season), and be sure to have the motor inspected and cleaned annually. Keep in mind that some warranties will be voided if you don’t have your furnace cleaned regularly.

Check Your Motor’s Power

If your motor suddenly stops working or the high-limit switch has been tripped, your first step is to check to see if there’s power going to the unit. If that seems OK, check the low-voltage control circuit, including the fuse. Make sure the circuit breaker hasn’t been tripped or a fuse blown. If that’s the case — and especially if it happens repeatedly — that could indicate a short in the motor. To check for a short, you’ll need to look at the windings.

Check the Windings

To check the windings for a short, you’ll need to measure the ohms. If that’s not on your list of DIY can-do’s, it may be time to call your local HVAC pro. But if you’ve got the skill and an ohm meter, you’re all set.

A typical PSC motor (or permanent split capacitor motor) will usually have three or four colored wires (often red, blue, yellow, and black) plus a white wire and two brown wires. Perform a resistance test with the white wire and each of the non-brown colored wires. You’ll want to see a resistance reading with each of the wires.

If you get a zero reading, you’re probably looking at a short. If you get an over-limit (OL) reading, you’re likely to have an “open” winding. In either case, it’s time to replace the motor. Your local HVAC dealer can help with that.

As for typical ECM motors (or electronically commutated motors), the winding test is much more complicated and you have to take the motor apart to get to the windings. This is a task suited for experts only, who can also be found using our convenient HVAC dealer locator.

Check the Capacitor

If your power is fine and you’ve not detected a short or an open winding in your PSC motor, then you’ll also want to check your capacitor. That’s what those two brown wires connect to. The capacitor assists in the motor running and gives it more torque to turn the blower wheel or fan belt. If that’s not happening, then the motor won’t start.

Checking the capacitor is a little more tricky because they’re usually pretty small, you’ll need a capacitor tester, and you’ll need to discharge the capacitor before handling it. If you’ve got that all lined up, the capacitor tester should show a microfarad reading within 10% of the rated capacitance. If not, it’s time to replace the capacitor.

If any of this feels like more than you’d like to take on, a lot of homeowners would agree with you. That’s just one reason to work with a local, reliable HVAC pro. Find one using our convenient dealer locator.

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