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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a nordyne MMHB-056ABHR-01 in a mobile home. It lights

Customer Question

I have a nordyne MMHB-056ABHR-01 in a mobile home. It lights up, runs for 30 seconds, then shuts off. It will lite up again in about 30 seconds and do the same thing. But if I hold the inspection door open it will run normal.
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.


The combustion air intake is restricted, too long, or sloped so that water has collected in it... OR... the pressure switch is going bad, has a bit of water in its 1/4" rubber hoses, or needs the nipples the hoses are attached to cleaned out with a paper clip wire.

Please attach a well focused, close up photo of the wiring diagram glued inside the service panel,you can use the paper clipicon at the right end of the toolbar at the top of this dialog box,Include a picture of the thermostat wire connections to the printed circuit board in the same area.

If there is no paper clip icon, look for the '+attach files' link at left of your send button.

I can mark it up with trouble shooting instructions. You will need a multi meter ($30 at a hardware store) and some experience working with appliances, let me know a lot about your skill sets in those regards.

We can go from there, if I miss you tonight I will pick your response up first thing in the morning.

Customer: replied 1 year ago.
There is no pressure switch. I was thinking that the combustion fan maybe is not pushing enough air into the chamber.
Expert:  Phil replied 1 year ago.

Hello again, if there is a combustion air fan, or inducer fan, there is a pressure switch in 99% of furnaces with such a fan.... the small percentage without a pressure switch use an air flow sail switch. I need to see the wiring diagram to coach you on it.


Customer: replied 1 year ago.
I am not there right now, will have to continue tomorrow.
Expert:  Phil replied 1 year ago.

That will work, I am in all day tomorrow also.