Nordyne M1MB090A Limit Switch Code

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Old 11-02-14, 02:17 PM
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Nordyne M1MB090A Limit Switch Code

I have a Nordyne M1MB090A upright forced air gas furnace that when first started for the year came on and operated properly for one day. I then noticed the blower running constant with no heat. Checked error codes and it flashed one steady flash indicating limit switch. I followed diagrams and seem to only find one limit switch. It is located up on blower panel. Took it out part #36 tx 11 L140-40 parimeters. I checked it at 100 ohms and it showed it open. I manually can activate the switch by pressing it in and closing the circuit. It seems to be working but I have no idea what to check next? I think it is getting good air flow as I can run it open. I can't locate a reset but I have shut the circuit breaker off for 5 minutes with no luck. It doesn't even cycle a heat up, it goes right to error. Any ideas? Thanks!!!
 
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Old 11-02-14, 02:42 PM
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Could just be a bad limit switch. If the furnace has been off for a while the switch should be closed.
 
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Old 11-02-14, 04:30 PM
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Thanks for the reply!
Do you mean closed as in no circuit? It shows continuity but I can push in the on the bottom (inside part) and disrupt the circuit. Does that mean it is bad? Thanks again
 
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Old 11-02-14, 06:02 PM
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I believe you will find two self-resetting limit switches on your furnace; a high limit and an auxiliary limit switch. Here is a link to the manual:

http://www.nordyne.com/literature/690a.pdf

Check page 29 and 30 for info. The wiring diagram on page 35 shows the auxiliary and the high limit switches. These switches trip due to an overheat condition usually due to low or restricted air flow such as a dirty air filter, obstructed return air ducts, or a dirty/clogged a/c evaporator coil.
 
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Old 11-02-14, 06:29 PM
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You have me confused now. In your first post you said the switch was open and pressing it closes.
Did you pull the wires off the switch when you OMHed it out?

I would buy a new switch.
 

Last edited by skaggsje; 11-02-14 at 06:37 PM. Reason: added info
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