Return to the Appliances Forum | Post a Follow-Up

 o
Testing CFM of Refrig Condenser fan. Is my motor slow?

Posted by etbrown4 (My Page) on
Thu, Jun 7, 12 at 12:13

Other than putting you hand in front of the fan, is there a reliable way to test the cfm output of a refrig condenser fan, or know what it should be?

I've seen a digital cfm tester at Lowes.

After cleaning the condenser coil, I still think I am not getting enough air through that coil.

It's on a SubSero 700, but the question really applies across the board to all refrigeration.

I know all ac motors are supposed to run at their synchronous speed, but I've heard of fan motors needing replacement from running slow.

Have others encountered a slow condenser or evaporator fan motor?


Follow-Up Postings:

 o
RE: Testing CFM of Refrig Condenser fan. Is my motor slow?

AC induction motors (most are) do not run at synchronous speed. They always run slower than that.


 o
RE: Testing CFM of Refrig Condenser fan. Is my motor slow?

And the SubZero fan may be controlled by electronics to run at a deliberately slow speed under certain conditions. SubZero customer service should be contacted about this.

If you could measure the cfm flow rate achieved by the fan (which is not so simple to do), what would you do with the information?

kas


 o
RE: Testing CFM of Refrig Condenser fan. Is my motor slow?

It would be great to compare the actual cfm off of the existing fan and motor with the mfg's spec!

Otherwise it's all guess work, and I'd like to avoid that. For that reason, it would be great to know what some pros have done when they have suspected an under performing fan and motor.


 o
RE: Testing CFM of Refrig Condenser fan. Is my motor slow?

I'd be happy to at least verify the actual rpm of the motor, and from there we could at least deduce that if the rpm is right then the cfm's must be! (assuming no damage to the blade)

I know the rpm is stamped on the nameplate. (I'm also aware that the motor might be variable speed.)

Is a meter available which will measure the rpm's of an electric motor? Anybody used one?


 o
RE: Testing CFM of Refrig Condenser fan. Is my motor slow?

A strobe light with calibrated frequency would allow measurement of the blade rate (per second). Dividing by the number of blades and '60' would yield the motor speed (rpm). Or, put a dot on a single blade and sync to it to get motor speed.

I wasn't aware SubZero specified their condenser fan cfm.

Measuring air velocity would allow computation of cfm, but only if flow were uniform over some relevant area. Non-uniform flow combined with blade tip spillage would make the measurement difficult unless the cfm were specified and measured on the other side of the condenser from the fan and integrated over the area of the condenser.

kas


 o
RE: Testing CFM of Refrig Condenser fan. Is my motor slow?

Problem hopefully solved, for now.

Ebay is loaded with digital tach's for $13 including shipping.
Once it comes in, I'll share my experience with it and a comparison of the measured rpm with the nameplate.

Not sure exactly how it works but I think there is a light or laser which reflects on reflective tape applied to one of the fan blades.

No strobe required and hopefully no math.


 o
RE: Testing CFM of Refrig Condenser fan. Is my motor slow?

Digital Laser RPM meter worked like a charm!

Subzero says it's a 1360 rpm motor and I got that plus or minus a few!

At least the condenser fan is ruled out, and I have a great little rpm meter.

Will have to look further to see why I get a service light most of the time. The service light on this unit is supposed to signify that the compressor is running for longer periods that it should. (The condenser coil could not be cleaner.)

Possibilities are: a thermistor, the sealed system and charge, and possibly a few others, I suppose.


 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!


Return to the Appliances Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.


Learn more about in-text links on this page here