[LazyPup]

I doubt very seriously if a 120/24v or 240/24v stepdown transformer could produce enough load to blow a 5a fuse. In almost all cases when a stepdown transformer fails the failure is in the secondary side.

I would be more inclined to believe that the motor bearings are dry and causing the motor load to increase as it runs or you have a run capacitor that is breaking down under load.

On both end bells of a motor there is a small diameter tube from the outer circumference of the motor to a reservoir surrounding the motor shaft. On the ouer end of the tube there is a tiny plug in the tube. In most instances the plugs are red plastic but on some motors they may be a small metal insert that looks like a rivet and may be painted the same color as the motor body. Inside that reservoir there is a felt wiper surrounding the sleeve bearing. The flt retains the oil and the bearings are porous bronze. The oil from the felt wiper passes through microscopic pores in the porous bronze sleeve bearing to lubricate the motor shaft. The oil ports should be lubricated with fine machine oil at least once a year, although in the real world they generally go unattended for years unless the unit is annually serviced by a trained technician, and even then there is no guarantee they are oiling the motor bearings.

In some instances if you catch a motor when it first starts to reduce RPM and oil the bearings you can save the motor, but generally if the problem has gone long enough that it is causing the bearings to partially seize under load and trip the fuse or breaker, it is highly unlikely that oiling the bearings will save the motor.

You can check the motor bearings by first checking the motor data plate to see what is the correct amperage for your motor; then attach a snap on amp meter to the common wire from the motor and measure the actual amps as the motor starts and runs. There should be a momentary spike in amperage as the motor first starts. That spike will normally be about 3 times the rated amperage for the motor, but the start amperage spike should only last about 1 to 2 seconds, then the amperage should drop down to the rated amperage and remain steady at the rated amperage. Continue monitoring the amperage, if it begins to climb significantly after the motor has run 10 or 15 minutes either the bearings are dry or you have a run capacitor that is breaking down under load.

NOTE: The amperage rating on the motor data plate is computed to a theoretical line voltage, however the line voltage at your location may vary significantly from the rating on the motor. Example, the motor may be rated at 125v 2a but when you measure the actual voltage at your location it may only be 110v. (line voltage may vary from 90 to 125v).

To get the most accurate measurement of the motor amps you must compensate for your local line voltage. Begin by multiplying the voltage x amperage rating on the motor data plate to determine the watt rating then divide the watt rating by the actual measured line voltage and the result will be the correct operating amperage for your motor at your location at the time the test is being made.

From our example;
the data plate is 125v x 2a= 250w.
The actual line voltage at your location at the time of the test is 110v so the correct run amps for the motor at this location should be 250w / 110v = 2.27a.

If you oil the motor and allow about 1 hour for the oil to saturate the porous bronze sleeve bearing before testing and it is still showing high amperage either the pores of the bearing are by now obstructed with dirt and debris or you have a bad capacitor.

The make capacitor testers that can test a capacitor under load, but they are rather expensive and generally not a tool that a homeowner would have access to. Capacitors are relatively inexpensive so when in doubt, change the capacitor. If that does not resolve the problem you will have to change the motor. On the upside, when changing a motor it is recommended that you always change the capacitor with it, so even if changing the capacitor did not resolve the problem you are not out any money because you should get a new capacitor for a new motor anyway.