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Furnace problem

Discussion in 'The Lounge' started by dogdaysunrise, Feb 11, 2006.

  1. dogdaysunrise

    dogdaysunrise 1/2 ton status

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    I have an electric forced air furnace and I am having a problem with the fan not shutting off. The elements are shutting off properly and the house stays and a nice 68 degrees, but the fan isnt kicking off. I thought it may have been the t-stat so I changed it the other day with no luck. I have been googling around but nothing really makes mention of the issue. I got a couple of ideas from my findings, but I dont really want to start throwing parts at it to see if it fixes it.

    Does anyone have any experience with this kinda stuff? If so, any ideas to test stuff?

    Thanks,

    Mike
     
  2. Jagged

    Jagged 1 ton status

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    Stuck relay? :dunno:
     
  3. Storm Trooper

    Storm Trooper 1/2 ton status GMOTM Winner

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    OK, lets start out with the basics.
    Does your thermostat has a fan on/auto switch? (is it in the auto posistion)

    Like Jagged said, the thermostat powers a relay that turns on the blower,
    some times they will either run through a time delay switch that keeps the
    blower running until the unit cools down (just time).
    Other units will have a snap disc that checks the temperature and shuts the
    blower off when it's cool enough. Either one can stick in the on posistion.

    If your not sure what it has, check the back of the blower door for a wiring diagram. Follow the hot lead (L1) from the blower motor back towards the power source. That way you can find out what the blower is powered with.

    Use your electical meter or tester to test the device for contiuity (power off).
    If the low voltage leads are disconnected, is the power still going through
    it back to the blower? If you still can't quite figure it out, take a picture
    of the wiring diagram and post it. If you figure out what it is, post it.
    I can help you figure any of that stuff out............piece of cake.

    Make sure your careful with the power, most electric forced air furnaces
    are powered with 220V. Hate to see you look like this -----> :yikes: :yikes:
     
  4. Thunder

    Thunder 3/4 ton status

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    Yeah to what storm tropper said. Check your thermo snap switch(s). Many times they fail to on position and the fan will run all the time. They are usually a round disk looking thing with 2 wires going to it. Usually located just downstream of the heating colis
     
  5. hi pinion

    hi pinion 3/4 ton status

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    Damn your good.:D Dabbling in heating and air are we? :D
     
  6. dogdaysunrise

    dogdaysunrise 1/2 ton status

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    Well looks like i got it fixed up guys. I opened her up and found the snap disk. There was a wire going to it, that had gotten black with corrosion. I chopped it and cleaned it, and it seems to be working like a charm.

    Thanks for all the help and the quick responses. The amount of knowledge from the diffrent backgrounds on this page makes it work the money all the time.
     
  7. dogdaysunrise

    dogdaysunrise 1/2 ton status

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    okay, i thought i fixed it... but I guess not. I see the thermo snap switches (or atleast they are what I believe to be the snap switches), there are 2 of them. There is also a 2 position switch that appears to turn the fan on auto, or just on. When I switch it to the On position and then back to the auto (?) position it seems to reset the snap switches and the fan shuts off. I will take some pictures of what I believe to be the snap switches in a couple of minutes. They look like relays so there is a good chance that they are them.

    If these are them, should I replace both of them? or just test to see which one is causing the problem?
     
  8. Storm Trooper

    Storm Trooper 1/2 ton status GMOTM Winner

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    1st show us a picture of them. Did you find the wiring diagram?
    I could do a lot more with a little more info.
    If your just going to replace them (can't hurt) and the are cheap enough,
    then I'd say go for it. Sorry, I might not get back to you right away because I've been working my tail off. I have a couple thousand customers and as of three weeks ago, I'm a one man shop (Puck!) I'm on call 24/7 and just finished diner (Sun - 11:10 PM).
    Even my customer said, "Dave have you lost some weight?"
    Anyway, I'll try to help out as I can.

    BTW-
    Wtf? You think I just plumb Jake? I do more heating work then anything else.
    My systems are among the finest in the country (well, at least the state).
    That's why I'm stuck in the Great white north of Colorado. $$$$$$ :D:D:D

    Things I can/Do/or maybe don't wanna do-
    Plumbing new and service.
    Heating work, hot water, steam, schorced air, AC, electric
    Solar, wood stove heated hot water.
    Electrical wiring controls and design
    Sewer cleaning and jetting, septic tank pumping and locating (not anymore!)
    snowmelt systems.
    use to be a union carpenter. Do pretty good as a general contractor.
    I've been a glazer building storm doors and windows.
    Gas piping of course.
    Fireplaces, pools and hot tubs (I wanna be a pool boy)
    appliance repair.
    Drafting & design. Blueprints.
    Profesional drinker.
    I chit, a bunch more but I'm burnt out, it's time for a shot
    and hit the sack. I need to get up early and fire my other service tech tomorrow.
    (long story..............)
     
  9. dogdaysunrise

    dogdaysunrise 1/2 ton status

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    Okay I will try and explain the wiring as best I can

    The White wire goes directly from one of the Hot wires off the main power block.

    The blue wire goes to the middle post of the switch

    The red wire goes to the (on side) of the switch

    The black wire goes to the left relay.

    blower.jpg

    relay1.jpg

    relay2.jpg

    switch.jpg
     
  10. Storm Trooper

    Storm Trooper 1/2 ton status GMOTM Winner

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    OK, that helps a bit. The yellow leads are the low voltage leads that control things.
    As you can see from you pictures, they go to the bottom side of what should be a fan heater control (snap disc - the round top switch).
    When the top blk leads send power to this switch, it heats up inside (mini heater) and turns on the relay (yellow leads) which should turn on the blower.
    I can't tell where the leads are going from the two relays below (made by Steveco- spst) but more then likely one of them powers the blower from the thermostat fan on/auto switch.
    All three of these parts shouldn't be very much money and it wouldn't hurt, if your stuck, to just replace them.
    As for the blower motor leads.
    Black = high speed
    Blue = med speed
    red = low speed
    the white wire should be a common (netrual)/shared wire.
    Normally the high speed is used for heating.
    the blue or red are used for when you just want to switch the fan on
    at the thermostat or for cooling (AC, if you have it).
    I hope this helps.
    It would still be nice to have a picture of the wiring diagram if you still need help.
    Dave
     
  11. dogdaysunrise

    dogdaysunrise 1/2 ton status

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    Dave your a good man, there is a wiring diagram that I will see if I can get a clear picture of. Its pretty old and faded however.

    As for what you are saying is the snap disc, there are 4 or 5 of those in a row coming from top to bottom till it gets to the relays. Unless you mean the yellow wires looping at the blower motor itself.

    Thanks again for your help I apperciate it very much.
     
  12. dogdaysunrise

    dogdaysunrise 1/2 ton status

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    Okay here is a pic of the wiring diagram. Im gonna leave it big because it makes it easier to see. The picture is actually tiny, but I player around with the focus and the macro to get it to work. Hopefully you can read it.

    IMG_0891.jpg
     
  13. hi pinion

    hi pinion 3/4 ton status

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    Oh yeah, whell my toilets are the best in THE WHOLE WORLD! :haha: j/k

    I really should be at work right now in fact:haha: this is wrong:haha:

    Sorry to interupt man. :D

    Jacob
     
  14. wasted wages

    wasted wages 3/4 ton status

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    See that silver can mounted to the blower wheel housing ?

    you need to take that off,, remove the wires,, and stick the terminals to your tongue-like a 9 volt battery and see if it's any good !! :haha: :haha: :haha: :haha: :haha:
     
  15. hi pinion

    hi pinion 3/4 ton status

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    Thats ,,,ha ha:haha: sorry for messing up your thread:haha:
     
  16. dogdaysunrise

    dogdaysunrise 1/2 ton status

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    so if i discharge the cap on my tongue it will make the fan work? excellent! i will go test it out right now, im gonna get my dog to do it though, Im not a big fan of the taste of metal.
     
  17. Storm Trooper

    Storm Trooper 1/2 ton status GMOTM Winner

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    That's better!
    MR 1 & MR 2 power the blower, not the snap disc's.
    The coil on MR1 is powered with 240 volts from R1 (relay1 /terminal 5) or R3 terminal 5.
    The coil on MR2 is powered with 24 volts from terminal G on the thermostat (fan on switch on thermostat).

    Notice the constant on switch listed by the blower motor? Do you know where that is on the furnace? It might have got turned on by accident.

    If not, and you have a voltage tester/meter, see if you have power at the coil contacts (1 & 3 ) of either relay MR1 or MR2.
    If you have 24V at 1&3 on MR2, turn the thermostat back to auto or disconnect the green wire going to terminal "G".

    If you have 220/240V at the 1 & 3 terminals of MR1, either relay #1 or relay #3 may have a stuck set of contacts (terminals 4 & 5 on both of them).

    I hope I'm not making this too hard.
    If you follow the power lead that comes into terminal 4 on MR2, it jumps over to T6. When this relay is energized by the thermostat (on/auto switch), contacts 4-2 close (turn on) and contacts 6-5 open (turn off), this sends power to the black lead on the blower motor.
    when this relay is off, power is allowed to go through contacts 6-5 and power contacts 4-6 on MR1
    power can flow through contacts 6-5 on MR1 and if the auto/cont. switch is on, power will feed to the red lead on the blower and keep the motor running.

    When MR1 is energized, it turns off power feeding through 6-5 contacts and feeds power through 4-2 to what they show as yellow for the blower. This is more then likely the blue lead to the motor, not yellow.
    If you don't run the fan in the summer for cooling etc. the only lead that is needed to the blower motor is the one that comes off contact 2 on MR1 and feeds the blue or yellow lead.

    I hope you can follow this, if not, let me know and I can show you how the power flows by coloring the lines on the wiring diagram.
    Time for bed...........later.
    Dave
     
  18. dogdaysunrise

    dogdaysunrise 1/2 ton status

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    Dave this is making sense to me. I will go and test it out when the problem reoccurs. Right now it is intermittent, it comes and goes as it pleases. To me it does sound like one of the relays is sticking. Im gonna phone around and find out what kinda of prices are out there for them, and replace them.

    I will keep you updated as to what the outcome was. Would it be possible that MR1 or MR2 is causing the problem?

    Thanks again,

    Mike.

    p.s. If you are ever having any cable, phone, or computer network issues, you make sure and let me know :)
     
  19. Storm Trooper

    Storm Trooper 1/2 ton status GMOTM Winner

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    Yes, MR1 is the main blower relay.
    MR2 is next in line to power it but if R1 or R3 should stick,
    they will power the coil to MR1.
    If the blower is running but there is NO power to the coil on
    MR1, then the R1 & R3 relays should be OK.
    That's the problem with electric forced air, it takes way to many
    relays and time delay relays etc. to make it all work.
    More relays make more chances of problems.
    The little snap disc's that go to each element have to delay coming
    on so each element comes on one at a time and keeps the power
    surge down. Anything electric like that WILL fail sooner or later.
    Don't forget to check continuity of each element since your in there.
    Relays don't do a dam thing when the elements are burnt out. :-)
     

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