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Miller Nat Gas Forced Hot Air issues

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ColdHouse
ColdHouse Member Posts: 94
in Gas Heating

just closed on our daughter home Friday and furnace acting up. Had tech out who said A coil blocking air flow and causing high temp switch to cut out. He removed A coil, thought fixed, but burner kicking in and out on long duration runs. Sometimes furnace continues entire heat cycle/stat satisfies, but gas valve does drop out and the glow plug comes back on and then gas ingnites and may run 10-15 minute or longer of less and do reignite all over again. Sometime needing completely breaker off reset, other times not.

Tech is hanging hat on high limit switch, which had to be ordered and two days out and its zero here, so we are 24hr baby sitting and resetting as needed.

My question, he said it can’t be jumpered due to a resistance being read by controls. Is there a way to test the high limit to confirm it’s bad?

Furnace is in double wide it’s a 1998 Miller Nat gas forced air. High limit part number is 6264370. I am debating on losening mounting screw of switch, sliding a metal washer to create air gap, retighten and see if that helps until parts here

Comments

  • Big Ed_4
    Big Ed_4 Member Posts: 3,408

    It could be the limit breaking down… The limit is a safety , don't jump out or repair , only replace …

    There was an error rendering this rich post.

  • ColdHouse
    ColdHouse Member Posts: 94
    https://forum.heatinghelp.com/discussion/comment/1884372#Comment_1884372

    We are desperate to get it to just run without being reset. I am very aware of the dangers of allowing the furnace to possibly over heat. My IR gun says plenum temp is at 97* where high limit is mounted and research tells me the switch is a 190* cut out. We are onsite non stop monitoring.

  • ColdHouse
    ColdHouse Member Posts: 94

    My main question is, how to test the switch? Tech says you can’t jumper, due to controls reading the resistance of the switch? If that is the case, I have VOM meter and can test the resistance, but what should it be? I know that apparently it completely opens up when it exceeeds 190*.

  • pecmsg
    pecmsg Member Posts: 6,872
    edited 1:08PM

    If the A-Coil was plugged so is the squirrel cage fan blade.

    Whats the temperature rise between the return and a supply?

    IR Thermometers are very inaccurate!

    ColdHouseBig Ed_4
  • ColdHouse
    ColdHouse Member Posts: 94

    Tech removed the A coil and also cleaned the squirrel cage fan which was very dirty as well.

    How do I check the supply and return temps? IR gun on the upper inlet and then on the bottom outlet covers? What should I use instead of an IR, or just take reading with a grain of salt?

  • pecmsg
    pecmsg Member Posts: 6,872
    edited 1:17PM

    Thermometer.

    Color, material distance all affect IR readings.

    Ideally, you're looking for 40 - 60° difference between return and supply.

    Did this tech recover all the refrigerant before removing the A-Coil?

  • ColdHouse
    ColdHouse Member Posts: 94

    I have digital type thermometers of all sorts I use for cooking. I will try to use one of those to checK supply and return temps. I was not present when A coil was removed, we took ownership of the home on Friday and was told the air was not working. The outside unit appeared to have been damaged significantly.

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