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Gas furnace blower will not kick on


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  • Gas furnace blower will not kick on

    I have a Coleman D.E.S 80 gas furnace model #2845C666.

    When the thermostat tells the furnace to blow heat, there is a fan that turns on (vent fan?), the ignitor glows, gas flows and flames start dancing and when the blower should turn on, it does not and the gas turns off but the fan (vent fan?) keeps going. I started having problems last winter.

    I have turned off the furnace, turned off the gas and then turned them back on. Last winter, this worked. I would reset it and then it would start working. The furnace worked for a month or so but now, the blower will not turn on.

    Any ideas? I have limited knowledge but from a logical standpoint, I seem to think the fan switch. I have attached the wiring diagram.

    Thank you in advance for any help
    Click image for larger version

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  • #2

    the first fan to turn on is the draft inducer motor. this causes an air flow up your chimney. look for an sail switch or air pressure switch at the outflow of this motor fan. if its contacts don't close, then nothing in the gas flow chain will operate.


    • #3
      It sounds like your draft inducer/vent fan and provingcircuits are working properly. This allowsthe ignition and the burner to work as well.
      Although I have never seen or worked on a Coleman unit, Isuspect that it works the same as most other furnaces. There is usually a fan switch that senses thetemperature of the heat exchanger. Whenthe exchanger temp rises to a preset level, the fan will come on and when itdrops below another level it will turn off the fan. Check this switch first. Make sure it is getting power. Then lower the ‘turn-on’ temperature (thereis usually a scale on the housing with a screw slot in it). Also, make sure that the ‘turn off’temperature is set to some level sufficiently below the ‘turn on’ temperature.
      Let us know what you find and how this gets resolved.


      • #4

        the blower switch is mounted in the plenum chamber above the heat exchanger. it is a helical spring that expands and imparts a rotational force to a set of contacts in the switch. there are two set points that can be adjusted. the first is cut in temperature, the second is cut-out temperature. in between is the proportional band or run time. this switch may also have another set of contacts that form the high limit cut-out.
        I've seen at a minimum two wires or as many as three wires going to this switch. one is common with two outputs.


        • #5
          have you checked the blower door safety switch ? will the blower even try to turn ?


          • #6
            gas furnace blower wont come on

            Hisorry bout your problem here lets see what we can do to get you going. GFirst off ,at your t stat turn the fan switch to on and lets see if the blower comes on. This will tell us if the blowers any good to a certain extent. If the blower starts up than what we need to look at is the control board. On a coleman if I'm not mistaken the blowers brought on by time. The blower relay that's on the main control board could have the relay points burnt fried. The board would have a burn mark on the back side of it. If you find this youll need a new replacement board.Now does the furnace go through the first steps of a call for heat? After you run the stat the first thing is a smaller motor turns on and clears the flue pipe (Chimney) this motor should run all the time the furnace hs flame burning.Theres safety switches that monitor the operation. After about 90 seconds then theres a device called the hot surface igniter. You will here a click than you will see a device light up bright red or orange this is what lights the furnace. after the hot surface ignitor turns on and turns red, you will here another click and that's the gas valve opening up to allow the gas to flow over the igniter and lite the furnace off. after its lit the furnace will keep burning and the blower can come on by a number of ways but I believe the coleman uses a timing method. The blower will start up if it doesn't then the furnace gets to hot and will shut down by an temp limit switch.If the furnace gos thru all these steps and doesn't come on the main control is your problem.


            • #7
              gas furnace doesnt come on

              Im sorry I didn't notice you had a diagram for the coleman furnace. This is a pretty easy fix here and shouldn't have to many issues. This blower motor only has a few components that could affect it. The Fan capacitor may not be putting any microfared out and cause an open circuit. Theres also a limit switch that's inline with power also that could be an open circuit as well. It looks like the system may have cooling hooked up t it so if the blower came on when turned the fan switch to on well the limit is open and wont let the blower come on in a lower speed. This repair without a meter can truly be any of these components so bare with me . if you got power coming into it and then your looking at the fan cap, the relay, thre limit switch,or maybe the motor itself. the common wouyld be ck the limit switch.


              • #8
                quick answer

                Go to your thermostat. Turn it fan "On"

                If it doesnt turn on, you might have a bad blower motor.

                Jim Martin

                Dallas Air Conditioning Service | Dallas AC Repair Service | Dallas Heating Service | 24-hour HVAC Technicians


                • #9
                  hey Jim, could you advertise somewhere else like the phone book maybe


                  • #10
                    Sorry. I thought it was OK to list my company website address. I have lots of good info on the website.

                    I apologize. Not trying to advertise.

                    I'm in Forney Texas, I doubt many people on the forum are in my area.

                    Have a great day,



                    • #11

                      doesn't matter where you are or whom you work for. if you can offer free help to other people in here, welcome. but if this is a plug for your company then please get rid of it.
                      for that matter I haven't seen anything constructive in your posting replies.


                      • #12
                        yea i went to your site Jim, saw a lot of info on how to get a quote, appointment or set up a service call but nothing regarding how to help the home owner help themselves. As you may have noticed, that is what this site IS about.