nortron furnace migraine

[luc12]

hello...i have a 4 year old(give or take) electric 25 kw nortron furnace....the fan drops to low when the t-stat tells it to shut off and it stays on forever...only way to shut it off is with main breaker...no switches were tripped or touched..everything worked fine all 4 years so it`s not a bad wiring job issue...the fan alone,no heat, decided to stay on a few weeks ago....there are three switches on furnace itself...summer switch is set to heating.....energy saver switch is set to cold weather..... fan control switch is set to automatic....there`s also a green light on the furnace which says t-stat on....t-stat controls are set to heat and auto....these switches have been like this all winter.....now fan won`t shut off..there is also an air conditioner hooked up to this unit....25KW, 240 Volt D Series Electric Furnace
Model 21D25....no model # written on furnace...not positive on model #....how do i trouble-shoot this problem so i can buy whatever part i need????which wires do i pull to test this and that?????please help....

[HayZee518]

the fan I'm guessing operates off a fan contactor or fan relay. there is an operating coil that keeps the contacts closed. if the operating coil got fried while the contacts were closed, mechanically they'd stay closed. the contacts could have welded together closed. if when you shut off the breaker for the fan you notice the contacts did not open then suspect welded contacts.

[luc12]

thanks for replying; I`ve attached a picture of the wiring so you can have a better idea of what`s what..hope it works....never done this before......I went to the furnace and my wife was turning breaker on and off and there was no clicking sound or nothing when the fan was turning on and off.....don`t see any contacts;just relays..i think the big red wire on the bottom right is the low power for the fan...i could pull that but then the motor would go straight to high ...probably not good....any help? thanks

[HayZee518]

I made a copy of your picture. I'll get it into "paint" and make some annotations as to what is there and re-post it later today

[HayZee518]

The larger area are your heat elements. the whitish circles are the element overloads. these are wired normally closed. the wires grouped together are the common(s) to all heater elements and go to one terminal on the main bus. The sequencers are wired into a control circuit somewhere else. as more heat is needed a sequencer will turn on and in turn turn on an element. look to the diagram under all the wires. it'll give you some idea of how this panel is wired.

[luc12]

OK; my best guess is the 240 volt relay...bottom right...the only reason is that the low speed red wire comes off of this to the fan motor....i know nothing about furnaces....that`s why i ask the people who do..that being said,what do you think?.....thanks for your help....

[HayZee518]

That being the case replace the relay.

[luc12]

so you agree it`s the relay?

[luc12]

update.....i went back to the furnace with breaker on and the t-stat set to off...fan was running on low...i pulled the red fan wire and fan shut off and i saw the closest element start glowing red....that now explains the fan being on...i didn`t notice the element was on before because with the fan running,the element doesn`t glow as much...now my question is why is that element on with the t-stat set to off?thanks in advance,anyone?

[HayZee518]

can you make a copy of the schematic diagram and somehow get it to me?