Richard and Rhonda
10-03-2011, 05:07 PM
I am posting to provide info that may help someone in the future.
The blower motor failed on one of my basment units. From the inside, the result is either no cold air, or a tripped circuit breaker. From the outside the unit makes a loud buzzing sound when it trys to start.
Here are the things I learned in the diagnosis of this problem.
If you hang an ammeter on the blower motor or the compressor motor it appears they are both pulling maximum amps. I eventually used a very complex technique to determine which one was locked. I put my hand on each motor. The buzz was definitely in the blower motor.
The problem with my motor, and most others that are referenced on this site, is that the bushings simply wear out, causing the motor to drag.
However, to be a little more scientific, here are some reference numbers you can use to check both the blower motor and compressor motor before you tear into the refrigeration system.
The resistance readings for the compressor motor were 0.6 ohms black to white, 7.5 ohms white to red, and 6.9 ohms red to black.
The resistance readings for the blower motor were 9.2 ohms black to white, 66.2 ohms white to red, and 57.2 ohms red to black.
The current system is wired to use a run capacitor of 20 mfd for the compressor, and 7.5 mfd for the blower. It also uses a start capacitor of 88-108 mfd wired in parallel with the compressor. The start cap uses special resistor that is temp compensated to disconnect the start cap after the motor is running. This little resistor, made by Ceramyte, part # CM O 305 C20 is kind of old school technology. I replaced it with a standard hard start capacitor made by Supco, available at any HVAC supply place and/or Amazon.com. The Supco is self contained on the disconnect.
I did get a replacement motor from Newell. My attempts at finding a suitable replacement through all the typical sources were not successful, and Newell's price was in line. I did take the old motor apart of course to see the failure. I will try to replace the bushings, however the motor shaft also appears to be worn, so I don't think it would last very long even with new bushings.
As far as replacing the unit, I initially tried to get the motor out of the blower housing. Wrong! It was much easier to remove the entire blower housing, four screws.
Hopefully, this will help you diagnose a similar problem, or better yet keep you from ripping out a perfectly good compressor only to find that's not the problem. That's where my head went when I heard the loud buzzing coming from the unit. Locked compressor. Then a tripped breaker. More locked compressor evidence.
The quick and dirty dead give aways on diagnosis were: no air blowing out of basement unit, the blower squirrel cage not turning, and the buzz originating at the blower motor.
Seems simple in hindsight, eh?
The blower motor failed on one of my basment units. From the inside, the result is either no cold air, or a tripped circuit breaker. From the outside the unit makes a loud buzzing sound when it trys to start.
Here are the things I learned in the diagnosis of this problem.
If you hang an ammeter on the blower motor or the compressor motor it appears they are both pulling maximum amps. I eventually used a very complex technique to determine which one was locked. I put my hand on each motor. The buzz was definitely in the blower motor.
The problem with my motor, and most others that are referenced on this site, is that the bushings simply wear out, causing the motor to drag.
However, to be a little more scientific, here are some reference numbers you can use to check both the blower motor and compressor motor before you tear into the refrigeration system.
The resistance readings for the compressor motor were 0.6 ohms black to white, 7.5 ohms white to red, and 6.9 ohms red to black.
The resistance readings for the blower motor were 9.2 ohms black to white, 66.2 ohms white to red, and 57.2 ohms red to black.
The current system is wired to use a run capacitor of 20 mfd for the compressor, and 7.5 mfd for the blower. It also uses a start capacitor of 88-108 mfd wired in parallel with the compressor. The start cap uses special resistor that is temp compensated to disconnect the start cap after the motor is running. This little resistor, made by Ceramyte, part # CM O 305 C20 is kind of old school technology. I replaced it with a standard hard start capacitor made by Supco, available at any HVAC supply place and/or Amazon.com. The Supco is self contained on the disconnect.
I did get a replacement motor from Newell. My attempts at finding a suitable replacement through all the typical sources were not successful, and Newell's price was in line. I did take the old motor apart of course to see the failure. I will try to replace the bushings, however the motor shaft also appears to be worn, so I don't think it would last very long even with new bushings.
As far as replacing the unit, I initially tried to get the motor out of the blower housing. Wrong! It was much easier to remove the entire blower housing, four screws.
Hopefully, this will help you diagnose a similar problem, or better yet keep you from ripping out a perfectly good compressor only to find that's not the problem. That's where my head went when I heard the loud buzzing coming from the unit. Locked compressor. Then a tripped breaker. More locked compressor evidence.
The quick and dirty dead give aways on diagnosis were: no air blowing out of basement unit, the blower squirrel cage not turning, and the buzz originating at the blower motor.
Seems simple in hindsight, eh?