nordyne mmhb090 blower won't shut off

Questions about repairs and parts for Nordyne furnaces, air conditioners and heat pumps for manufactured homes including Intertherm, Mac and Miller brands. Click here for Nordyne parts.

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barnbiketom
Posts: 4
Joined: Wed Aug 07, 2013 9:09 am

Fri Aug 16, 2013 7:23 am

gas furnace runs and heats fine but sometimethe cirulation fan won't shut off or shuts off a
LONG time afterwards. is it the fan switch or relay?? how to tell?? thanks tommie


DaleM
Posts: 385
Joined: Wed Apr 07, 2010 10:07 am

Wed Aug 21, 2013 12:28 pm

You will have to look at the schematic but the relay or switch is bad.

barnbiketom
Posts: 4
Joined: Wed Aug 07, 2013 9:09 am

Sun Aug 25, 2013 9:39 pm

Thanks... I can read schematics ..was auto tech for 20 yers BUT THIS schematic I am NOT at all familiar with the legends .. the relay and switches.. I think the fan switch is 'normally open' that is when it hits 115 it closes.. but that relay has me confused.. which are the coil legs and what are the other four.. 2 are hooked together or ????
i might just try to measure the voltage drop on the switch next time it malfunctions... no voltage between the legs of the switch will mean it is closed ..right???
I'll try to attach a pic of my furnace diagram.. tommie
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DaleM
Posts: 385
Joined: Wed Apr 07, 2010 10:07 am

Mon Aug 26, 2013 10:36 pm

Coil legs are usually 1 and 3. Check to see if the temp switch is causing the blower to activate or the relay. The relay is for air conditioning blower ON function, the fan switch is for heating blower ON. The relay is double throw type. When no power is to it, the fan switch energizes the blower motor. When power is fed to the relay the blower comes on immediately for the air.. Disconnect the fan switch and tape the leads, if that solves the problem the fan switch is stuck closed. If not then the relay is stuck closed. Hope this helps.

barnbiketom
Posts: 4
Joined: Wed Aug 07, 2013 9:09 am

Tue Aug 27, 2013 5:17 am

thanks SO MUCH. this unit has no AC so in other words, the circ fan is only controlled by the fan switch right? the relay should never come into play..??

the unit heats and the fan comes on, it just sometimes stays on for too long and last time it stayed on forever until i tapped on the case.. i feel now it is/was the fan temp switch but i will know how to check next time it acts upQQQ


DaleM
Posts: 385
Joined: Wed Apr 07, 2010 10:07 am

Wed Aug 28, 2013 7:25 am

No air conditioning, it's the fan switch.

barnbiketom
Posts: 4
Joined: Wed Aug 07, 2013 9:09 am

Wed Aug 28, 2013 4:47 pm

Thanks Dale!!!
i appreciate your information and expertise!!

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