ACHRNEWS

The Case of the Yo-Yo Motor

April 7, 2008
A technician is shown removing a control module from a 2.3 ECM. The 16-pin connector is the tip-off that the control doesn’t belong to a communicating 2.5 motor.


MONTGOMERY COUNTY, Md. - The service call that just won’t die is every technician’s worst nightmare.

It is yo-yo syndrome: a job that keeps on breaking as soon as you get back to the shop, making you go back and forth. Soon you’re thinking it’d be easier to just bring along a sleeping bag and move into the homeowner’s basement. It’s enough to make you pull your hair out.

Yo-yo syndrome was happening at Hoffacker’s A/C and Heating.

A reliable Bryant Evolution furnace kept faulting out, causing callback after callback. All said and done, it took two months of ongoing troubleshooting and five return trips to the homeowner before everything was squared away.

Owners Don and Mary Hoffacker are not new to the HVAC game. With 30 years of experience in a small residential community where some of the country’s most educated consumers live, the Hoffackers have built a reputation on fast, reliable, and professional service.

It’s the sort of shop where the owners don’t mind getting their hands dirty alongside 21 technicians, and the company spares no expense in providing its people with the latest diagnostic tools and service training. Their Montgomery County, Maryland-based dealership has even been nationally recognized by the Air Conditioning Contractors of America (ACCA) as a “Residential All-Star.”

“We’ve been very fortunate to have the group of technicians that we have,” said Mary. “They’re very skilled, all of them are either NATE-certified or on the road to certification, and we’re always sending them to new classes to help keep our guys on the cutting edge.”

TRIP 1: ONE FRIED MOTOR

The original call was simple enough. The blower wouldn’t run, and the motor control was visibly burnt. The motor did not run correctly when attached to the TECMate Pro, a troubleshooting tool designed specifically for field-testing an electronically commutated motor (ECM). Clearly, an electrical short had blown out the electronics, so the technician checked grounding and ordered a new ECM control module.

“You have to have the right tools for the job,” said Don. “TECMate is a plug-in-and-go troubleshooter that helps you determine if you’re dealing with a dead motor, motor control, or something else in the system. It saves a lot of time, which is why every tech in our company has one.”

He also noted that technicians can save the homeowner a lot of money by checking the control and the motor module. With a fully working motor in place, most OEMs can provide a control-only replacement part instead of scrapping the entire motor and control.

TRIP 2: A NEW CONTROL

There happened to be a new variable-speed ECM control for Bryant systems of the same horsepower waiting in stock back at the shop, so technician No. 2 returned to the home, control part in-hand.

Slight problem. Variable-speed systems take advantage of programmed features that are specific to each piece of equipment, meaning that the replacement part has to be an exact match to the original model, not just the same horsepower.

Unbeknownst to the tech, with the incorrect control installed, the fix didn’t work. Using the OEM system manual, the technician made sure that the furnace board was sending the correct signal, and used a TECMate to double-check the motor.

Things were starting to get tricky. Suspecting it was a connection problem, the technician ordered a new wiring harness for the furnace board and motor. It was also time to send in Frank.

TRIP 3: SOLUTION MAN

Frank Thompson is good at what he does. He is Hoffacker’s solution man with nearly 10 years on the job and NATE-certification in gas furnaces, air conditioners and heat pumps. When there’s a problem job like this furnace, Thompson gets called in to solve it.

“Field service can be a bit like diagnosing appendicitis,” said Thompson. “Sometimes it’s an obvious problem and easy to fix, other times the symptoms are strange enough that it leaves you wondering if the problem is the motor, the furnace board, the electrical work, or something else.”

He added, “There’s a temptation to just throw parts at the problem, but you really have to get in, understand the problem, and address the root cause.”

With a newly installed harness, a motor that ran in troubleshooting mode, no discernable electrical problems, and correct signals coming from the board, Thompson knew the problem: an incompatible motor and control.

TRIP 4: CALL FOR BACKUP

Thompson called back to the shop to double check the part number. Sure enough, the part didn’t match. A quick call to the local distributor and a new part was ordered. Upon receiving the correct part, one special ordered part later, Thompson returned to the homeowner confident that the new part would finally put the problem to rest. Success.

Well, not completely.

The new control allowed the motor to run, but the blower would never turn off. On the bright side, at least it was progress.

“We sell a lot of the systems, and this was actually the first time we’ve seen a motor issue,” notes Thompson. “There are a lot of ECMs in the field that are pretty old, but they’re still operating. In this case, everything checked out but the system still wasn’t working correctly. It didn’t make sense, so I decided to call the OEM directly.”

The Bryant technical support group agreed - it didn’t make sense. So far, the problems were caused by a wrong replacement part, and this new issue smelled like more of the same. If the shop was sure that it had the correct part, then the manufacturer’s advice was to check the furnace ground connections and try another replacement control.

Hoffacker’s was soon to find out that they didn’t have the correct part after all.

TRIP 5: A NEW HOPE

It just so happened that later that week Thompson and three other technicians from Hoffacker’s attended an ECM training session in Baltimore.

“I could go on and on about the training session. We picked up a lot of useful tips, including information about the specific motor we were troubleshooting,” said Thompson. “For example, a Bryant Evolution systems uses a ThinkTank™ ECM. It’s the only smart, communicating motor in the HVACR industry, which also means that we needed to use manufacturer procedures instead of our TECMate tools for testing the motor module.”

As part of the class, each technician also received a copy of the ECM Service Guide, a field manual for troubleshooting the motors. With new training and a comprehensive troubleshooting guide, Thompson was ready to put the mystery of the funky yo-yo motor to rest once and for all.

“I read the manual for everything, and I’m a lot better off for it,” he said. “It’s important. You’ll never memorize every aspect of every piece of equipment you’ll come across in the field, and new technology guarantees that you’ll come across a curveball or two if you can’t keep up.”

The guide backed up much of Thompson’s experience so far: don’t assume that the motor has failed, match the replacement control to the specific OEM model, and pull on the harness instead of the wires to avoid damaging the furnace-board connector. The next step in the troubleshooting process was to cross-reference with the motor identification chart found in the ECM Service Guide.

Looking at the chart, Thompson knew the problem immediately. An identification sticker attached to the replacement model showed that the part was for a ThinkTank 2.3 motor, but the 16-pin wiring harness from this furnace only had five control wires - a sure sign that he was dealing with a communicating 2.5 motor.

Thompson called the OEM to verify the replacement module. The last seven digits of the part code were exactly the same, but there was an “AE” instead of an “EA.” A local distributor had the correct module in stock, and one quick part swap had the furnace up and running.

THE YO-YO STRING GETS CUT

“After I found what was causing the problem, I felt pretty sheepish because we were just running around with the wrong part. Looking back, it always seems simpler, but the key here was education,” said Thompson.

“There’s never a cent spent on education that’s ever used in vain - it will always repay you many times over. I was glad to have this problem fixed, but if it weren’t for training and that service guide, we’d still be scratching our heads to this day.”

For now, it was quitting time. The yo-yo had finally gotten its string cut. In the end, it was the Hoffacker’s commitment to training and equipping their technicians with the right tools for the job that solved the mystery. That’s one lesson that is definitely worth taking to heart.

GE ECM by Regal-Beloit is a residential HVAC manufacturer of ECM technology. The company manufactures mechanical and electrical motion control and power generation products serving markets throughout the world. For more information, visit the company’s Website at www.thedealertoolbox.com.

Publication date: 04/07/2008