HVAC Blower Motor Operation and Current Draw during Airflow Restriction! ECM vs PSC

[@douglieberman6406]

The ecm is very amazing also because I have taken ohm readings of the internal windings and they read from 3 terminals the same resistance , as 12 ohms each as though it is considered position windings almost energizing 2 windings in a particular position to spin one way or the other !

[@jimmysegovia2688]

thanks, Craig awesome video man.

[@phillipjoy8191]

One of the best.THANKS for all you do.YOU have a great book also.😊

[@dcrams16]

Best teacher in the game

[@7x779]

I wish he would have done this demonstration with the same voltage and size of units so we can see the difference in efficiency if there is any between the motors These three are all way different sizes and voltages,

[@realestateservicessaleshea99]

Thanks again for the videos! 🥃🥃🍺🍺🍺🎳⛳

[@wlouis7583]

A blower conversion video would be nice.

[@Joe_Joe_The_HvacMan]

Great video! I’ve been wanting to do one like this for a long time. Well done Craig!

[@acservicetechchannel]

Thank you for watching! 👍

[@7x779]

​@@acservicetechchannelcan you do a video where you show the three different types of motors in identical units and voltages so we can see the difference in amp draw between them?

[@7x779]

​@@acservicetechchannelI'm also curious if you know, do the ECM Motors speed up the impeller to an even greater RPM then the PSC does when it's unloaded by blocking the airflow? It's clear that the PSC motor and impeller is being unloaded with airflow blocked, that's why it speeds up and draws less power at the same time ? Thanks

[@jamesmooney5348]

Wow, this is a great video! Thanks

[@edlauren9434]

Last November I ran into a dead ECM blower motor on a store RTU. That RTU was ~12 years old and that motor was OEM only replacement, $600 and 2 weeks wait (at least). So, it was November with freezing temperatures.... I just installed regular PSC motor and a contractor that would get 24V directly from the thermostat. So, the entire repair was less than $500 (including the PSC motor and the contractor). The customer is happy, everything works great. From now on I would thing twice if I go back ECM or just replace it with PSC motor and close the case.

[@sprockkets]

It depends. You can easily replace an X13 style motor and program them or just use ones that mostly do the job. If the unit is constant air flow and uses communication, that's not really an option. Sure, you can get a kit that does translate it over if you are tired of doing replacements. But the expense is the part that is made to work exactly as it should with a module, not because the motor in it of itself is special.

[@franciscog175]

That's like choosing to conmute on a donkey, instead of a gas vehicle.

[@edlauren9434]

Yep, that donkey did the job pretty well and still working fine… for 1/3 of the price and… it was in the local store. However, the ECM motor was only from the manufacturer, two weeks waiting… And it was 23F outside… So, GO donkey! :)

[@7x779]

​@@franciscog175please do explain such a drastic difference. Have you put a meter on the same size units with one with a PSE motor and the other with an ECM motor and seen how much difference there is?

[@mavamQ]

My second ECM motor on our HVAC failed, when my B-I-L said, let me put a PSC motor on it. It has been fine since. The first ECM just died, replaced under warranty, the second developed a bad bearing and rumbled, I had ordered bearings when My B-I-L installed the PSC.

[@martineucza486]

Thank you Craig!

[@John-dp3ln]

Excellent.

[@jericosha2842]

Superb examples. Thanks!

[@kennethlobo4420]

Thank Craig, great video

[@miguelquiroz1550]

Great explanation ...Thanks!

[@Mudcat597]

Thanks for the info and demo. 👍👍

[@edwardgarza5104]

Great video, I was always under the impression if the blower motor has less air to move the amps would be lower just like the PSC motor did. Good to know that the ecm motors do not work like that.

[@sprockkets]

Technically, they do. But they are programmed to compensate.

[@biblebloopers946]

@@sprockkets How do the ECM blower motor is know what the static pressure is? Is there a sensor taking static pressure in the unit that's talking to the blower motor? I'm confused of how it knows

[@sprockkets]

@@biblebloopers946 it knows via the amount of "drive" it needs to reach a certain rpm.

[@biblebloopers946]

@@sprockkets thank you and one other question. With a constant torque ECM motor, if you get a g call and a y call to the ECM motor at the same time then what takes priority?

[@sprockkets]

@@biblebloopers946 y does. Same for constant cfm motors. Essentially it picks whoever is higher.

[@dennisqwertyuiop]

great demo

[@Ricoswavaey]

Great video!

[@jynnandtonnyx]

Love it! Great video 😊

[@raulgarcia528]

Exelente explicacion amigo

[@TheDave5619]

Legend! Thanks for the info!

[@scha0786]

Good stuff

[@MathCuriousity]

May I ask - with PSC, you mention after blockage and static pressure increase, the current lowers. But if the current lowers shouldn’t the fan speed lower too?! But it’s a constant rpm so it can’t right? So what gives?!

[@a1a918]

Liked the video. Theres one motor you didn't address. ECM constant torque Variable speed [ Pulse width modulation ] in Carrier products.

[@embeddedgirl]

they'll still behave the same way. just tested this myself.

[@douglieberman6406]

With AC voltage applied to the motor , for instance a motor with common to start winding resistance and common to run winding resistance and then from start to run winding resistance. I would use ohms law and take the voltage from common to run , common to start and start to run across a capacitor and divide the resistance into the voltage and get the current ! I would get 3 different currents. Because reading AC current, which is alternating like voltage peak to peak it is difficult to get a correct current reading unless we had an oscilloscope with measures cycles per second . Also related to the revolutions per minute I can divide 60 by the revolutions per minute and get the revolutions per second of the actual fan blade! Please reply!

[@7x779]

Your comment is interesting, as part of the sales pitch I've heard over the years for ECM motors, is that they'll automatically compensate for duct irregularities or restrictions, or high static ductwork buy automatically increasing the motor speed and airflow to compensate I'm still not sure one is better than the other. I would like to see a direct comparison of two identical systems with the same identical blowers and ductwork and static pressure, all designed properly, and with all three motors compared side-by-side in those identical systems My subjective experience just being out in the field, I haven't noticed a big difference in how much power and ECM motor is using compared to an old fashioned PSC motor I just worked on a 4-ton package heat pump with a 4 amp 3/4 HP PSC motor and it was drawing 2.8 amps how much would an ECM motor be using?

[@douglieberman6406]

The brushes of a y motor actually are offset to spin one way or the other!

[@mobilecommunicationsnetwor5268]

If you set dip switches for a low speed on the 16 pin ECM motor would that negate the problem? Stop the jet engine noise? Would the blockage be obvious, if you didn't have static pressure testing device available for testing? Test by removing the filter and opening the door to the furnace and a visual inspection, acceptable test?

[@sprockkets]

Without a static pressure measurement you are in the dark. If you set air flow too low that will cause its own issues.

[@mobilecommunicationsnetwor5268]

@@sprockkets I appreciate you taking the time to reply.

[@7x779]

Most of the time the problem is dirty filter or a plugged up evaporator coil, or homeowner shut off too many Supply registers in unused rooms thinking they would save money on the power bill. And one time it was in 18-in return flex duct that would get sucked in and collapse on itself when the unit came on

[@MathCuriousity]

Lmao it suckrd itself into a collapsed state? I thought the fan turning on actually increases static pressure so why would it suck into collapsed state?

[@JC-sc9rx]

I'm really new to the trade how do I know which wire of the 10 wires to put the amp clamp on on the plug to the blower motor? Thanks

[@7x779]

I don't know for sure but if you look at the schematic you can see which are the line voltage wires going into it, and I would put the meter around one of those On a simple air handler or furnace like these, it works just as well to put it on the actual line voltage wire coming into the entire unit because the only other thing using power besides the motor would be the Transformer and circuit board which is insignificant

[@douglieberman6406]

I know we can get the correct current readings from straight direct current through a clamp current meter!

[@7x779]

Close enough especially when you're doing a direct comparison using the same meter on all three

[@keithwiebe1787]

I've been playing with my Longwood (propane over wood) and without wood in the chamber the blower would cycle a few times before temp came up in the room. I used a piece of cardboard on one side of ducted fan and now motor runs continuously but probably draws less amps as it's creating less pressure. Also, less air over an A coil would lesson the demands on the condenser unit wouldn't it? You wouldn't be transferring as much heat out of system. Now if condenser was restricted of airflow it would cause a rise in pressures and increase in compressor load.

[@jc80]

Thank you for this info, I have a solar system and this helped improve our power draw on the unit. However I also noticed in my testing that our air handler is drawing 6 watts from out outlet when it is not even running. Is that normal?

[@7x779]

Yes. The Transformer has to be working 24/7 or nothing's going to work

[@douglieberman6406]

Also amplitude in AC power!

[@Josh-px6xb]

So to test amp draw on a variable speed blower motor or ECM motor you just put the clamp meter on the incoming power leg?

[@7x779]

Yes, unless it's winter and it's a heat pump with heat strips that are running, then you need to disable or turn off the heat strips

[@biblebloopers946]

How does the variable and constant to torque ECM blower motors know what the static pressure is? Are there static pressure sensors in there that are talking to the motor?

[@7x779]

No, it senses how much torque it needs to keep the motor at a certain RPM, probably by monitoring how much current is needed at that RPM.

[@joshuahatridge3833]

Have always wondered if there was a way to know what the amp draw should be. The rating on the motor doesn’t seem relevant in my findings. Would door removed amp draw be the best for comparison?

[@sprockkets]

No. Door on is the proper measurment. With PSC that could mean over amps with a door off. Experience will tell you what you should expect. Typically 1800 cfm should produce 4.2 or so amps on 240v.

[@7x779]

It depends on the condition of the system. Door on with a plugged filter or coil or collapsed return duct or homeowner which closed off a whole bunch of Supply ducts is it going to really throw your reading off

[@douglieberman6406]

Please show the readings of a psc motor across the windings with a meter!

[@7x779]

May I ask why? What benefit would that be to anyone?

[@rocker8692]

Neato

[@JohnnyJr396]

That makes sense with these motors. On a psc propeller fan , why does the current increase with air restriction?

[@7x779]

Because that's what happens with a propeller fan the physics Dynamics are different on squirrel cage blower. That's why when you hold your hand on a vacuum cleaner it actually unloads the motor and you can hear it speeding up and if you put a meter on it you'll see it will draw less power

[@MathCuriousity]

But PSC is also called “fixed speed” so even if the load decreases and current decreases ……why would the fan speed up? First off I would think it’s built to resist changes in speed otherwise why call it fixed? Secondly, lower amp draw to me would be relative to spinning at the same speed it did before.

[@chriseh09]

For a constant torque motor, IE X-13, would you describe the taps as “torque taps" more so than a “speed tap” as I understand the torque of the motor is changing to overcome higher static rather than the speed. With a constant airflow motor, IE variable speed, that would raise the airflow to overcome higher static. Am I to understand this incorrectly? Thanks for all you do!

[@sprockkets]

Correct.

[@7x779]

From my understanding no motor produces any torque at all until a load is applied to it, and in the case of a fixed unchanging blower wheel size, and assuming the duct size, static pressure, etcetera is also not changing, then the only way to increase the torque load on the motor is to also increase the speed or RPM on the motor to try and force more air through which in turn put some more of a load on the motor which requires the motor to produce more torque

[@douglieberman6406]

Also , there are terms like impedance, reactance , capacitance and inductance and conductance!

[@7x779]

Thanks for the glossary, I'm sure this will make me an amazing Tech and cut my diagnosed time in half

[@UltraHydrophobiccoat]

I have an old motor rated 10 Amp, the supply house staff said I have to use a equal or higher Amp replacement motor. He said the control board would send 10 Amp current to the motor, if I put a lower Amp motor it will be burned out. I think that’s other way around. Put in a lower current rated motor will be safer. Anyone has any ideas? Thanks

[@7x779]

I'm sure my reply is too late for what you needed to know but perhaps it will help others. A circuit board a relay does not send any current, all it can do is connect the circuit and send voltage to the motor. Then the motor will draw whatever current depending on the size and load on the blower wheel. The amp size rating on the motor that you're talking about doesn't mean the motor is going to use that many amps, what it means is that it is capable of being loaded down up to that level of using that number of amps, in the example you gave, that 10 amp motor should not be drawing more than 10 amps, if it is then it's too small for the load it's on For example, I just worked on a package unit with the factory OEM 3/4 horsepower 4.0 amp motor, that was actually drawing only 2.8 amps working fine In your case, if you knew how many amps your old motor was using before it went bad, you could choose a new motor with that amount of amps or more For example, when in a bind or an emergency late night or weekend Etc and I couldn't get a 3/4 horse motor, I have put a 1/2 horsepower instead, and it still didn't even use its Max amp rating and it worked fine One time to get the guy going, and he didn't care, I replaced a 3/4 or 1 horsepower ECM motor in a 5-ton package unit with a half horsepower PSC motor, I was concerned it might not be enough and it was still only using its rated amps or just a little under. And homeowner said the volume of air was about the same as it ever was.

[@BrettWae]

Wonder why the amperage increases with the constant torque / variable speed. How does the motor know it has to work harder?

[@RockoRocko-rz7kx]

The motor doesn’t all the magic is in the module(computer) and the ifc (mother board)control in the furnace

[@pcpolice7937]

It has a static pressure sensor that tells it to speed up as the static in the duct increases. A constant speed motor has no static sensor tied to it and as the the duct plugs up the blower simply moves less air and in turn the motor draws less amps

[@7x779]

​@@pcpolice7937really? I've worked on hundreds of units and never seen one with a static pressure sensor regardless of the type of motor it has Also, what do you mean by constant speed motor? I don't know any such thing exists in the real world

[@7x779]

Brett, I have wondered the same thing. The only explanation I can think of is that the module must sense when the load on the blower wheel is reduced by having air flow restricted which unloads the impeller and causes it to speed up. To compensate, the module speeds up the motor even more to place a load back on it to increase the airflow to attempt to compensate for the restriction How else can you explain the current draw increasing when blocking the airflow actually reduces the load on the blower wheel? Ps.. a lot of people get the wrong idea that when you block airflow on a squirrel cage that it's actually loading it down and making it work harder It does not load it down more to understand this simply put the hand over your vacuum cleaner hose and listen if the motor speeds up or slows down. It speeds up because you're unloading the impeller by blocking the airflow

[@pcpolice7937]

⁠@@7x779Have you ever heard of a company called “Grainger”? They offer thousands of different HP’s, frame configurations, shaft sizes and voltages of constant speed motors. I did not say that this system has a constant speed motor. And if there is not static pressure sensor in the system depicted, where does the motor get the input to speed up. Maybe go back to the third grade and learn how to read

[@stephwaylonwells3218]

👍

[@embeddedgirl]

and this is why so many ECM blower motors fail!! don't use an ECM blower motor on a system with terrible ductwork, IT WILL FAIL. The constant argument of ECM blower being shit compared to PSC motors bothers me, they're not shit at all, they just don't work in poorly designed systems lol. I've always had a rule of thumb where the absolute most critical section of an HVAC system is the ductwork. If the ductwork is terrible, no matter what unit you install, it will never work correctly. Fix the ductwork and everything will operate as it should.

[@MathCuriousity]

Answer my queries friend.