Preventive Maintenance

[JP]

I pulled apart my furnace to clean the 21 years of dust accumulation, everything went fine but during the clean and inspect I noticed the middle limit switch was charred in half in fact the wire and lead came off in my hand. My technical skills are on point and I like to think there isn’t too many things I can’t fix, however my knowledge of furnace repair =’s a big fat zero . I really need your help in this area.

My furnace is an Electric Coleman Model 3400A816 with a two wire thermostat.

Looking at the schematic I see the middle limit switch hooked to the middle heating element and than to the sequencer. Visual inspection of the three heating elements (now I’m a furnace noob remember) seams to be ok, no charred parts, no breaks, and I used a soft bristle brush to clear any dust accumulation. Also looking at the right side of the sequencer where the middle heating element is attached I can see a little bit where the insulation looks as if it got a little hot but no signs of failure.

I know I need to replace the limit switch, that’s a given.

Should I replace all 3 limit switches or just the one that is charred?
Should I replace the sequencer as well?

Any thoughts on this would be great. Thanks in advance for your time.

r/JP

[hvac1000]

[quote="JP"] I pulled apart my furnace to clean the 21 years of dust accumulation, everything went fine but during the clean and inspect I noticed the middle limit switch was charred in half in fact the wire and lead came off in my hand. My technical skills are on point and I like to think there isn’t too many things I can’t fix, however my knowledge of furnace repair =’s a big fat zero . I really need your help in this area.

My furnace is an Electric Coleman Model 3400A816 with a two wire thermostat.

Looking at the schematic I see the middle limit switch hooked to the middle heating element and than to the sequencer. Visual inspection of the three heating elements (now I’m a furnace noob remember) seams to be ok, no charred parts, no breaks, and I used a soft bristle brush to clear any dust accumulation. Also looking at the right side of the sequencer where the middle heating element is attached I can see a little bit where the insulation looks as if it got a little hot but no signs of failure.

I know I need to replace the limit switch, that’s a given.

Should I replace all 3 limit switches or just the one that is charred?
Should I replace the sequencer as well?

Any thoughts on this would be great. Thanks in advance for your time.

These are the part numbers for the limit and sequencer control in your furnace.

3400-3151 Limit Switch o-175, c-125 NOTE I only show one limit switch listed.

3115-3571 Sequencer

Here is the page that you can order from

http://www.mobilehomerepair.com/ColemanElec.html

Usually hot spots happen when the connectors become loose on the above parts. This inrurn cause the wires to overheat and become looser usually till the wire fails and the heater no longer works.

I would replace any burnt or crisp wire.

I am a firm beliver in spare parts. Nothing like having the furnace go out when it is zero and not have the part to fix it on hand.
You could replacre the known bad part and keep the other new part as a spare just incase.

Remove and replace the wires exactly like they are labeled and located.

[JP]

What is your reccomendation on replacement wire, looks as if a couple of the pieces need replacement?

[hvac1000]

I have always used high temperature wire. The jacket does not melt when hot. A good multi strand quality wire shouls do. Also check size and also and replace with like same or better. Usually 10 guage wire.

[Robert]

Hi,


We sell all necessary wire, terminals and molex connector plugs for furnace wiring here:


http://www.mobilehomerepair.com/FurnaceElec.html


If anything is needed and it's not shown, let us know. We can most likely get it.



Thanks,
Robert

[JP]

Excellant.

Thanks for all the help

Very much appreciated.

JP

[Robert]

Hi JP,

You're very welcome, happy to help.


Take care and best wishes,
Robert