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York Furnace Blower issue

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  • York Furnace Blower issue

    I have a York furnace model PCMU-LD12N076B furnace that is 15 years old. The house is currently winterized and the heat is turned off. The problem is when I turn the heat on to show the house, the furnace goes through the proper sequence and the burners light. The fan limit switch clicks at the proper temperature but the blower does not turn on and the furnace goes into thermal shutdown. Once the unit cools off, it will function normally - the blower comes on without any problem.

    It is frustrating as I only get ONE chance to troubleshoot the problem per day... Last night, I checked the output of the fan control switch and when the fan control switch reached temperature (about 125 degrees), the fan control switch clicked and I had 120V at the output of the fan limit control switch but no blower operation. After I reset the unit, it functioned normally.

    I am now going to manually turn the blower motor on by selecting the FAN ON ode from the thremostat. If the blower runs, I would think the blower motor and capacitor are OK. If the motor won't turn on, then the issue may be in the capacitor or the motor itself.

    I'll then monitor the voltage as close to the motor as possible and see if it receives line voltage during the furnace cycle. Is there anything that I may be overlooking? Thanks!

  • #2
    Shot in the dark

    Isn't this a Luxaire instead of a York? If it was a York, it would be a P2UDD___ anyway: When it didn't start, did the motor get hot? Did you measure the MFD of the capacitor?
    Anyway, I can think of two possible issues, and either one is a guess:
    1. The fan & limit switch could be failing in a way that the contacts for the 120V to the fan will close and you'll be able to measure 120V, but there's not good enough contact to carry any current. We see this occasionally and it can be a real stumper for the service guys. You could measure 120V, but when there's a load on the circuit, like a blower motor trying to start, then the voltage will drop out almost completely. This doesn't explain why it would work once it's overheated once, but it could be that after one sequence of heating / going out on limit / resetting / the whole works has heated up enough that the points within the fan switch are now making better contact.
    2. The fan motor could have a "flat spot" in the shaft / bearings. This is something I've never been able to actually see or prove, but it's been the only believable explanation in several cases. The blower seems to stop in a certain position from which it can't start. Our technician will go there and turn the blower wheel and it turns easy and smooth. He'll check the capacitor and current draw and everything will be just peaches. Cycle the blower on and off and give it time to stop.... 9 times out of 10, or maybe 19 times out of 20 it will start up fine, but occasionally, it will stop in that "flat" spot. Whatever the reason for the failure, replacing the motor (sometimes after a callback) takes care of the problem.
    Hope this helps.


    • #3
      Re: York Furnace Blower issue

      Thanks for the information! I didn't know it was a Luxaire but now I do. There is no brand identification emblem on the outside - only a "Central Environmental Systems, York, PA on a label with the model & serial # on the inside so I assumed it was a York.

      I'll put my Amprobe on the lead to the motor and monitor the current to see what/if the motor is drawing during the start-up. If the motor starts and runs in manual ON mode, I can conclude the motor and capacitor are fine. I will also check the capacitor with my capacitence meter to see if it is 7.5 mfd +/- 6% as stated on the label.

      Another thought is to have a jumper wire temporarly connected at one end of the fan switch and when the blower won't come on, bypass the switch. If the blower then runs, I'd say the fan/limit control switch is bad.

      I'll post my findings but it may take two days to get enough data.


      • #4
        Re: York Furnace Blower issue

        Well, I found the problem... It appears that the motor bearings are bound up. I rotated the disc on the fan limit control switch and the blower motor buzzed... I then jumpered around the fan limit control switch and the blower motor still buzzed. I then attempted to rotate the squirrel cage and it was difficult to move then broke free.

        Next, I started the furnace and it was all fine. The blower motor has no oil ports on it. I'm going to see if I can disassemble the motor and lube the bearings. If that fails, I guess I'll have to replace the motor.

        Thanks for all the help!


        • #5
          Re: York Furnace Blower issue

          sounds like the problem..squirl cage should spin freely even with motor off. soo sound slike bad motor.

          Old timer tech should me a neat trick...IF motor not runing...give it a spin if it runs then capacator is bad...


          • #6
            Re: York Furnace Blower issue

            I checked the capacitor with my capaitence meter and it read 6.864 mfd. The spec on the cap. is 7.5 mfd +/- 6%. The cap falls out of the tolerance range but I don't think it is the problem because the squirrel cage was difficult to turn and then freed up once I rotated it. That was with the power off.

            I am going to see if I can disassemble the motor and lube the bearings. If not, I guess I'll have to replace the blower motor.


            • #7
              Re: York Furnace Blower issue

              bearing are usaly the time and hassle....get a new motor...besides once it starts to go....Murphys law will bite u in the butt on the coldest day of the year.....remember to turn the power off before removeing it...even 110v hurts. and mark the u can put them back in the right place. removeing the cage from the shaft can be a pain..oil...lots of oil...they make a puller for doing it...but with some time and effort usaly can get one off the motor shaft...DO NOT smack it with a hammer.....mushroom the motor shaft and your SOL getting it off....been their done that......OH get a new capacator too..always replace cap with a motor...its $10 and you will waste that in gas going back to the parts store.....its not a hard job to do....but take your time...not a I got 30 min before I go to work let me do this job...

              Let us know how it turns out.


              • #8
                Re: York Furnace Blower issue

                If you do need to impact the shaft use a hard wood or plastic hammer. If you hit it with a steel hammer like EG said you'll do damage and really have your work cut out for you. Remember this is not alloy steel that's been hardened. It's soft and even hitting it on end with a brass hammer can flare the end over. Then it really is (*&^%$# time.

                If you're lucky the motor has ball bearings (only if you're real lucky) which can be pulled off and replaced but my bet is it has sleeves with oil wicks which have dried out. In that case it really is best to replace the motor and capacitors. There will be worn grooves in the shaft and the sleeves will be egg shape with wear. Adding oil might let it turn but it will really wobble.

                While a motor rebuilding shop could fix it up, the total cost including labor would make replacement look like the only right choice. If you can deal with W.W. Grainger more than likely they have the needed replacement motor in stock or can have it to your branch in a day or two.
                Last edited by Woussko; 01-30-2008, 11:27 PM.


                • #9
                  Re: York Furnace Blower issue - Update

                  I removed the blower assembly yesterday afternoon and disassembled the motor, fan blade, etc. and cleaned everything. I disassembled the motor and discovered the bearings were dry but there was not any visible damage to the shaft. I re-lubed the bearings and the shaft with bearing grease and reassembled the motor. After sitting in my garage overnight, the fan blade turned freely this morning so I think it is fixed. I'm going to install it and test it today.

                  Thanks for the help!