5-ton Trane system, 0.8 TESP, blower failed after ~2 years — how concerned should I be?

tejvem · September 16

I have a 5-ton Trane system serving about 3,054 sq ft.

Outdoor unit: 4TTR5060N1000AA
Indoor furnace/blower: S8V2D120M5PC, variable-speed ECM

Original blower motor failed after about 2 years and was replaced under warranty.

Static was measured twice at about:

Return: -0.35 in. w.c.
Supply: +0.45 in. w.c.
TESP: ~0.80 in. w.c.

The system currently cools well at 76–77°F, humidity is generally 48–54%, and room-to-room temperature difference is about 3°F after prior balancing.

One tech calculated duct capacity at roughly 2,120 CFM return and 2,165 CFM supply, but that was based on duct sizes, not instrument-measured airflow.

Trane’s blower tables for this furnace show performance data through 0.9 in. w.c., which is why I’m trying to understand how to interpret the 0.8 reading in real-world use.

My main questions:

Is 0.8 concerning enough to investigate further on a variable-speed ECM system that otherwise performs well?
Could 0.8 reasonably contribute to an ECM blower failing after only about 2 years?
Would you first measure actual CFM, blower setup, filter pressure drop, and coil pressure drop before changing any ductwork?
How do you interpret a manufacturer blower table that publishes airflow through 0.9 when 0.5 is often quoted as the design/rated static?

I’m trying to determine whether this is a genuine restriction issue that should be corrected or simply a higher-than-ideal but common operating condition.

pecmsg · September 16

first I hope they registered that equipment so you get the full 10 years warranty.

See how the contractor deals with it. Is that .8 the calculated number of the controls or the actual numbers tested with the manometer

EBEBRATT-Ed · September 16

ECM motors fail. You can do a conversion from ECM to PSC motors. They sell kits for that. If you have to pay for a new ECM motor you will realize why.

tejvem · September 16

Thanks for the response. The @ pecmsg 0.8 was an actual field measurement with a digital manometer, not a number calculated by the furnace controls. The tech measured about -0.35 in. w.c. on the return side and +0.45 in. w.c. on the supply side.

I later checked the exact test locations and found the +0.45 supply reading was taken after the evaporator coil, so that 0.8 was not measured at the correct furnace TESP points. My furnace nameplate shows Maximum External Static Pressure: 0.70 in. w.c., so I’m going to have it retested correctly.

On the warranty, unfortunately the equipment currently shows the 5-year base parts warranty, not the 10-year registered warranty.

tejvem · September 16

@ EBEBRATT-Ed Thanks for the suggestion. Mine is still under the Trane parts warranty for now, so I’d probably stay with the OEM ECM motor while it’s covered. My main concern is figuring out whether the static pressure or airflow contributed to the first motor failing after only about two years.

Have you actually done an ECM-to-PSC conversion on a Trane S8V2 or similar variable-speed furnace, and did it affect airflow control or comfort?

pecmsg · September 16

.8 is not bad. Most systems are .6 or higher.
is this a zoned system?

GW · September 16

you type:

“I later checked the exact test locations and found the +0.45 supply reading was taken after the evaporator coil, so that 0.8 was not measured at the correct furnace TESP points. My furnace nameplate shows Maximum External Static Pressure: 0.70 in. w.c., so I’m going to have it retested correctly.”

I hate to be so pessimistic- can you take pics where these measurements were taken? Wrong spot then these numbers are useless. You would think all the decent technicians out there nowhere to take the measurements. But I would not bet my life on it.

if you have the energy to take pictures, take them from several steps back and try to draw an arrow. If you take the picture too close, I won’t have any frame of reference.

.08 doesn’t alarm me at all.

do you have a zoning system or is this just one thermostat?

Something doesn’t add up though- the tech used his duct-u-lator for that estimate? Thats a reasonable method to get a basic guess. If he guessed reasonably close, then something isn’t adding up perfectly well

HVACNUT · September 16

Having a 2 year old ECM motor fail is not exactly atypical even when static pressure is in range.

mattmia2 · September 16

https://forum.heatinghelp.com/discussion/comment/1903994#Comment_1903994

especially given there are still parts and designs around that were compromises to get around covid shortages.

jesmed1 · September 16

An AC evap coil can add anywhere from 0.1 to 0.4 IWC or more to your TESP, depending on how clean or dirty the coil is. So at a minimum you're probably already at 0.9 IWC when you add in the coil, and possibly over 1.0.

You can plot the data points from the chart of CFM vs TESP on graph paper, then extrapolate the curve beyond the 0.9 max they give you. It won't be exact, but if you approximate the curve you can get a good idea of CFM at your measured TESP.

At some point the CFM's can get low enough that the furnace will start shutting down on high limit, which is not good for the heat exchanger if it happens repeatedly. We had that problem with our church's furnace, which turned out to have unacceptably high TESP because the installer screwed up the return plenum sizing. We had no recourse because there wasn't enough space in the furnace room for a proper-sized return plenum, so we were forced to lock the furnace in low-fire mode to keep it from overheating. So now our new furnace limps along at 40% rated capacity. But at least the ECM won't burn out.

So if your max spec TESP is 0.7 and it's actually 0.9 or higher because the installer messed up on duct sizing, I would put the pressure on them to fix it. They'll say you can't prove the higher TESP caused the ECM to fail, then you say they can't prove it didn't.

Take a look at the ECM lifetime chart in the following HVAC blog. A typical ECM running at 0.5 IWC can last 15 years. A Typical ECM running at 0.8 IWC or higher has an expected life of 2 years, which is right when your ECM failed. Putting a new ECM in without fixing the high TESP is just setting up for another failure in 2 years.

https://northernonehour.com/blog/high-static-pressure-hvac-symptoms-fixes-twin-cities/

hot_rod · 12:02AM

Power issues can take out motors also. Surges, lightning, bad grounding.

The motor itself or the control module on the motor?

5-ton Trane system, 0.8 TESP, blower failed after ~2 years — how concerned should I be?

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