The blower motor plays an extremely important role in forced-air systems. It’s the trigger that circulates conditioned air throughout the home.

Blowers in older furnaces generally employ single-speed permanent split capacitor (PSC) motors while many newer furnaces use variable-speed electronically commutated motors (ECMs). Knowing how to troubleshoot and diagnose problems with these motors is an essential skill an HVAC technician must possess.


Blower motor breakdown can be the result of anything from old age to failed bearings, high amp draw, electrical failure in the windings, dirt accumulation, and more.

“The most common cause is dirt accumulation due to lack of maintenance,” said Tom Beaulieu, president of Bay Area Services Inc. in Green Bay, Wisconsin. “In very old residential systems — or, more commonly, in commercial systems — there could be a belt-drive blower. In those cases, excessive belt tension can be a cause. Tight belts place undue stress on the bearings, causing premature wear. Otherwise, normal old-age issues, such as bearing failure, cause seizing, which leads to massive electrical failure. A less common cause is insufficient voltage to the blower.”

The first step in diagnosing blower motor failure is to check to see if there is demand for the blower. If there is, and the blower is not operating, then it’s likely either a mechanical failure or an electrical failure, said John Boylan, general manager of Lakeside Service Co. in Brighton, Michigan.

“We check for mechanical failure by testing if the bearings are good and if the wheel spins freely; then, we check for electrical failure by first verifying that the circuit board is applying the correct voltage to the blower,” he said. “If that is good, then we check the microfarads on the capacitor to see if there’s a short or open on the capacitor. If the capacitor is good and there is no mechanical failure with voltage applied to the motor, it’s an electrical failure.”

“If there’s power going to it, the capacitor checks out, and the motor still doesn’t run, it’s bad,” Beaulieu added. “Or, it could be that the motor does run but is very noisy and drawing high current. That means the bearings are worn and causing excessive drag.”

Ed Kittle, operations manager at Howald Heating and Air Conditioning in Indianapolis, said the module on ECMs is often the culprit and replacing it will solve the problem the majority of the time.

“It takes about four screws once you get the housing out,” said Kittle. “Then, you plug it back in. There are a couple of tools out there [for testing motors], like the TECMate [from Genteq]. You plug it into the motor and hit a button, and it tells you if the motor is good or bad.”

While recurring blower motor failure is uncommon, it does happen, and finding the root cause is required in order to prevent the motor from failing again.

“If it’s dirt, it’ll be quite evident,” Beaulieu said. “If it’s power-related, a meter reading, under load, will tell you what’s going on. Triple check there is the right matched set of pulleys and the proper belt size.”


Whenever possible, motors should be replaced with the same make and model, Kittle said. This is especially important when it comes to ECMs in newer high-end furnaces.

“The key thing on an ECM motor is you have to replace it with the OEM ECM,” Kittle said. “A lot of those motors are programmed at the factory for that particular furnace — you just can’t pull one off the truck, stick it in, and say, ‘Here you go.’ It won’t work. They’re programmed for that equipment.”

Boylan also said it’s standard practice to replace blower motors with like motors. “OEM direct replacements are stocked on our trucks,” he said. “Install the motor according to the manufacturer’s instructions, always ensure you have the correct rotation on the blower wheel, and perform post testing to verify proper operation of the motor. Don’t guess the blower size, and be sure to verify performance after installation.”

Beaulieu said he’ll replace the motor with an OEM motor depending on the age of the furnace. “If it’s less than 5 years old and under a parts warranty, we’ll get an OEM replacement,” he said. “That usually means going back the next day.”

Bay Area Services’ technicians also carry a limited amount of universal-fit motors in their service vans to use as temporary replacements when the need for heat is critical, Beaulieu added. “We offer the Evergreen ECM retrofit motor when the homeowner has to purchase a new motor and the furnace warrants it. We carry two sizes — ¼-½ hp and ½-1 hp — that fit most applications.”

No matter the cause of the blower motor’s failure, Beaulieu said it’s important to make sure the equipment is cleaned and maintained during the service call.

“Take the time to clean the furnace thoroughly. That includes the secondary heat exchanger, the evaporator coil, etc.,” he said. “Measure the supply voltage to the blower as it’s running to be sure there is adequate power supplied. Measure the current draw when complete to make sure it’s within proper parameters. Don’t just replace [the motor] and run — check things over thoroughly. Tension the belt properly, if there is one.”


When a blower motor does fail, Beaulieu said it is often a good time to tell the homeowner to “consider upgrading the equipment.” Sometimes, that means a new system, but it can also mean upgrading to a more efficient, reliable blower motor.

“Most frequently, we install them when we have customers with airflow issues and correcting the ductwork isn’t an option,” Boylan said. “We also offer them when we perform energy audits and the equipment is less than 10 years old with a PSC fan.”

The only hurdle to upgrading to an ECM is the higher initial cost, Boylan said, though educating the homeowner can help overcome that issue.

“If you want to increase your service tickets by asking techs to become salesmen, ECM retrofit motors are an easy solution,” Boylan said. “Just be sure to teach your service techs about the technology, and give them some collateral to educate homeowners. If you offer options every time, you’re guaranteed to sell more. It’s an easy way to raise average invoices and customer satisfaction.”

Publication date: 12/7/2015

Want more HVAC industry news and information? Join The NEWS on Facebook, Twitter, and LinkedIn today!