Suburban Furnace Model # SF42-2303 Blower Motor very slow starting

[Travelingman 1]

My furnace has 13.2 Volts going into the furnace and while in full operation the volts going into the furnace only drop to 12.8 volts.  Here's my obstacle:  The fan is very slow starting it's rotation, like low voltage.  Imagine a jet engine starting very slow and in about 30 seconds she's full blast.  Runs great through the furnace thermostat set point.  Goes through its normal cool down and then shuts down correctly.  Time, both operating and idle time make no difference.  Can be off for 12 hours or maintaining the set point temperature it still starts like a jet engine.  I have inspected the fan and there appears not to be any drag on the motor.  This winter starts my third year with this obstacle.  At times I think it might just die on me.

 

[darsben]

Then for the $100.00 or so I would replace the motor. Sounds like the bearings are going bad

 

[Gary RV_Wizard]

Check the voltage at the fan - sometimes there is a loss from the power board to the fan. If the voltage is still good there, it's time for a new motor.

 

[Isaac-1]

The model is probably an SF42 not 8F42

 

[Travelingman 1]

I will pull the furnace out and check the voltage at the motor.  Thank you.

 

[PancakeBill]

Just replaced the motor on my SF-42 furnace, if you have not yet gotten to it, let me share some things I learned.

1- pretty good you tube video on it, but some extra points here.  I pulled furnace out of the housing, the video mentions it is only 1 screw because the other screw is not accessible, most builders don't put it in.  The housing is not that difficult to pull out.  I went with it was probably not installed, and thought out was stuck,  a little wiggling and it came out.  The screw WAS installed, so I broke the bracket in the back. !!!  It supports the heating chamber at the back.  Some JB Weld tacked it back, and fortunately it did not open the chamber.  Be careful if that. 

2- ti remove the Allen set screw on the big squirrel cage fan, he mentions a long Allen to break loose.  That was difficult to get in there, what I did was line up the half circle blade with the top of the housing.  On mine it lined up with the 4 in the SF-42 sticker on the top.  a small hole drilled in allows the Allen to go thru and align with the set screw.  The other advantage is it helps you align on the shaft in reassembly.

Some of the gasket material may be a little brittle, be careful.

Good luck, it was a world of difference.  Quiet heat!  It took me about 2 hours start to finish.  Would have been faster if I had my crescent wrench where I could find it.