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Blower not coming on

Ruffinitagain
Ruffinitagain Member Posts: 5
in Gas Heating

Hi,

The blower in my Lennox EL180UHE upflow furnace isn't coming on, although it fires up just fine. Yep, out of warranty by a year.…I tried replacing the thermostat, and that didn't help, but saw a reverse voltage polarity code, so I checked with the multimeter and the voltage difference was fine. Then I replaced the 42J3201 transformer on a hunch with no joy….

Any suggestions? I'm not getting a read between the circ terminal and the fan terminal, so I'm concerned that the board may be compromised…

ENR in central NJ

mattmia2

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,853

    Can you post a pic of the wiring diagram?

    That furnace has an ECM motor which is more difficult to troubleshoot. There are you tube videos on how to do that or call a professional.

    Replacing parts will do no good until you find the problem. Two terminals on the motor should have constant power the rest of the wires are for control of the motor speed.

    Those motors are $$$$$

    mattmia2
  • HomerJSmith
    HomerJSmith Member Posts: 2,635
    edited December 2024

    Sometimes there is a thermo-disc sensor on the blower housing. It may have tripped. There is a lag time from when a heater fires up and the blower starts, this prevents cold air in the ducts from blowing into the building until the temp in the heat exchange rises. That furnace probably has a trouble shooting section in the manual that may help you.

    With the thermostat calling for heat, take the blower door off the furnace and reach in and spin the blower cage and see if it turns easily. If it does, hold the door switch closed for several min and see what happens.

    Unplug the blower wiring connection to the board and re-plug it back in. Unplug the power first from the wall, tho.

  • 109A_5
    109A_5 Member Posts: 1,909

    Hello Ruffinitagain,

    So far I can't find a wiring diagram. There may or may not be a temperature sensor on the heat exchanger for the blower start, seems like the blower is timed-on delay is controlled by the board. Maybe you can verify that the board can actually engage the blower by using other features like the air conditioning.

    image.png

    https://tech.lennoxintl.com/C03e7o14l/VIu12Ch2uV/ehb_el180uhe_1904.pdf

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • 109A_5
    109A_5 Member Posts: 1,909

    Wiring diagram here

    https://www.questargas.com/ForEmployees/qgcOperationsTraining/Furnaces/Lennox_EL180UHE_IOM.pdf

    If I had to guess and it is not the blower motor, I'd say a relay on the board or a solder joint to the relay K5, K6 and/or K7.

    image.png

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • HVACNUT
    HVACNUT Member Posts: 6,456

    Is there fan if you switch the thermostat to fan on? That should be a different speed through a different relay on the board.

    SuperTech
  • Ruffinitagain
    Ruffinitagain Member Posts: 5

    Thanks, folks! Great ideas

    Yes, that's the wiring diagram from the inside of the lower door panel.

    No, the fan doesn't go with the "on" setting (vice "auto").

    I will definitely try to get the fan going in cooling mode to help diagnose.

    I'd read somewhere that there might be a red button somewhere, in case of a trip condition, but didn't find it.

    Regards, ENR

  • Ruffinitagain
    Ruffinitagain Member Posts: 5

    and the fan turns real easy

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,853

    The red button is a thermal overload device on the motor. Most furnace blowers don't have those anymore. They have an overload but it is auto reset….no button

  • worldclasshvac
    worldclasshvac Member Posts: 31

    The modules go on them quite commonly. Wheel will spin just fine. Fan on should make it run. Simple test is take a stick volt meter and make sure there is power to the black wire in the 4 pin harness. The pins are ground neutral power and common. If the board gave you reverse polarity that means it's sensing power and neutral are backwards. Anybody done electrical work recently?

  • Ruffinitagain
    Ruffinitagain Member Posts: 5

    Thanks, Folks

    No electrical work recently 🙂

    Well, I've been out of town but finally got around to trying the system in "cool" mode. The fan doesn't work in that mode either, AND the outdoor compressor/condenser unit also doesn't start! Is this confirmation that the board is bad? Or perhaps a replaceable part on the board?

    ENR

  • HVACNUT
    HVACNUT Member Posts: 6,456
    https://forum.heatinghelp.com/discussion/comment/1825735#Comment_1825735

    It doesn't mean anything without an electrical meter to prove it.

    Can you jump R and G at the board? At the thermostat?

  • SuperTech
    SuperTech Member Posts: 2,494

    It sure sounds like the motor is shot to me. Since it's out of warranty it might not be a bad idea to install a PSC motor and a RIB relay to bring the fan on. Probably much less expensive than a replacement ECM motor.

  • 109A_5
    109A_5 Member Posts: 1,909

    Multiple things inoperative, common denominator (common cause), does everything have the correct power, stuff don't work without power.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • Ruffinitagain
    Ruffinitagain Member Posts: 5

    Update: I replaced the ECM FM14 (X13) motor module and the furnace ran for two hours before cutting out again with an open limit switch code. The vendor knew my furnace model and supposedly programmed the DIP switches before shipping...

    So, I cut power and waited an hour. With the power back on it ran for 23 minutes before stopping again…this time with the reverse polarity code again. No cycling, as the house temp never got past 60degF

  • pedmec
    pedmec Member Posts: 1,142

    Run the unit with the blower door compartment off. Hold the door switch closed with your fingers and create a heating demand. When the blower motor starts to spin release the switch and check the rotation of the motor by looking at the fan blades as it slows down. The blower should be scooping the air. This will tell you whether it is rotating in reverse.

    Ruffinitagain
  • 109A_5
    109A_5 Member Posts: 1,909

    Hello Ruffinitagain,

    Well as I alluded to in my last post in this thread, I'm thinking there is an AC power issue, an intermittent AC power issue. The blower is probably the highest load, draws the most current in the furnace.

    I don't know the exact code setting criteria for the codes listed below, but I bet if they were due to actual wiring errors they may set almost instantly. Example; the Hot and Neutral wires are reversed.

    image.png

    Since the "Reverse Line Voltage polarity" code seems fairly consistent so far. I believe the board may (in part) use the Equipment Ground or Earth Ground as a reference for the "Reverse Line Voltage polarity" code detection, but since in your case it does not set instantly, as if the furnace was wired into the building electrical system incorrectly.

    I suspect (intermittently, load dependent) the Neutral to Ground voltage is increasing above a certain specification under load, like a blower motor attempting to start and/or the differential increases over time if the blower does successfully start (poor connection heats up over time). Usually the voltage differential between the Neutral to Ground is very low since the Neutral is supposed to be bonded to Ground at the electrical service equipment (like in the main circuit breaker panel).

    Long story short, I believe there may be a poor connection in the Neutral conductor somewhere in the AC power circuit. It could be in the furnace or actually in the building wiring. It could be a defect in the bonding between the Ground and the Neutral.

    A multimeter may not be fast enough to capture the event, unless the blower actually starts. I would try to measure the voltage Neutral to Ground where the power enters the furnace when an attempt to start the blower occurs (don't blink, you may miss it). I would also inspect the integrity of all the Neutral connections all the way back to the main circuit breaker panel.

    Be safe when working with AC power, or get specialized help.

    BTW if the blower drop out due to a power issue and the heat exchanger is hot, it may trip a code like this.

    image.png

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
    Ruffinitagain
  • 109A_5
    109A_5 Member Posts: 1,909

    Here are some more thoughts.

    You originally stated, " Any suggestions? I'm not getting a read between the circ terminal and the fan terminal, so I'm concerned that the board may be compromised… "

    On image below, not sure measuring CIRC to FAN is a valid test for anything (Orange). CIRC is on the primary side of the transformer and FAN is on the secondary side and the thermostat needs to be in the proper modes to close the correct relays. The voltage may be odd, like in the 144 or 96 VAC ball park.

    Addional things I would measure. Does the 120 VAC to to the furnace remain stable during the startup stages ? At L and N for 120 VAC at the blower motor (Blue). Also during a call for heat I would measure from 24 V COM to Heat (Red), K5 needs to be closed (Violet). Also 24 VAC at RO1 and RO2 (Violet), however if the thermostat works the 24 VAC is probably at RO1 and RO2.

    The thing is when the furnace is working normally these tests will probably be normal and if an error code is set everything shuts down.

    The 0 VAC (Blue) on the left is what I was referring to in the previous post. When the unit acts up, does the inducer motor seem to change speed briefly at the moment the blower should start up ?

    image.png

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System

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