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
nordyne mmhb090 blower won't shut off
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- Posts: 4
- Joined: Wed Aug 07, 2013 9:09 am
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
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
You do not have the required permissions to view the files attached to this post.
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.
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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
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
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- Posts: 4
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Thanks Dale!!!
i appreciate your information and expertise!!
i appreciate your information and expertise!!
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