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pryan67

Yes, I really needed this

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So, a couple of weeks ago I noticed that the fan on our furnace/AC was constantly running...

 

no big deal, right? Turn it off at the blower...replace the thermostat...ours was many years old as it was...

 

 

so I put a new one in...same problem...

 

looks like I probably need a new control module...I was hoping I'd have a 200 dollar expense this week... :angry:

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What is the brand? I assume you have central air? What type of thermostat?

 

 

yep..central air...neither air nor furnace works from the fan standpoint (fan stays on regardless)

 

thermostat was a thermochrome III by honeywell. I replaced it with a new honeywell...same pinout, etc...

 

I'm going to have to try to clean the flame sensor...since the furnace also won't light when we turn it on...

 

 

The part I need is a 50a65-843...which is what I had to have replaced 4 years ago :(

 

at least that's what it's pointing towards...

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What is the brand? I assume you have central air? What type of thermostat?

 

 

yep..central air...neither air nor furnace works from the fan standpoint (fan stays on regardless)

 

thermostat was a thermochrome III by honeywell. I replaced it with a new honeywell...same pinout, etc...

 

I'm going to have to try to clean the flame sensor...since the furnace also won't light when we turn it on...

 

 

The part I need is a 50a65-843...which is what I had to have replaced 4 years ago :(

 

at least that's what it's pointing towards...

 

If I get a chance I will put a bug in dh's ear, see if he has any ideas for you. What brand of ac/furnace?

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What is the brand? I assume you have central air? What type of thermostat?

 

 

yep..central air...neither air nor furnace works from the fan standpoint (fan stays on regardless)

 

thermostat was a thermochrome III by honeywell. I replaced it with a new honeywell...same pinout, etc...

 

I'm going to have to try to clean the flame sensor...since the furnace also won't light when we turn it on...

 

 

The part I need is a 50a65-843...which is what I had to have replaced 4 years ago :(

 

at least that's what it's pointing towards...

 

If I get a chance I will put a bug in dh's ear, see if he has any ideas for you. What brand of ac/furnace?

 

 

Thanks, I appreciate that...I don't know the model of furnace or AC offhand...but I'll find out when I get home...thanks

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When ours does that it means the flame sensor needs to be cleaned, but I'm guessing you weren't running your furnace.... :lol:

 

This happened to us as well....and the furnace was only a couple years old at the time. :glare:

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hubs said (mind you since he can't see it) a bad limit switch?

 

 

 

I thought that as well, but I can't find it :( From what I understand, it's a box similar to a light switch box (2X3 inches or so)

 

only thing similar to that is a black plate just above the burners that has 2 wires...can't get at it to tap it readily though to test it...maybe since I'm off work today I'll try to pull that out and see what it is :)

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hubs said (mind you since he can't see it) a bad limit switch?

 

 

can't find anything that looks like a limit switch...

 

I'd hate to replace the board if we don't need it...

 

unless the switch is part of the controller?

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well, I haven't replaced the controller board yet...

 

there's a diagnostic LED on the board that's supposed to flash when there are issues...and nothing happens...no light at all...

 

I CAN light the furnace manually...but then it still runs forever...

 

I just would hate to replace the board if I don't need to...

 

anyone have suggestions of what else to check? Can't find a limit switch anywhere, (basically, I KNOW the controller board is shot...but I want someone to tell me "no, it's not that...simply flip the hidden switch under the burners" or something like that :) )

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Almost sounds like a shot relay somewhere to me either electromagnetic or triac based. Would have to poke around in its brain with a multimeter before I could really figure out what was screwed up.

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Almost sounds like a shot relay somewhere to me either electromagnetic or triac based. Would have to poke around in its brain with a multimeter before I could really figure out what was screwed up.

 

 

 

bummer...so there's no "fix everything switch"... :)

 

I'll just break down and order the controller board...there's not much else there other than a couple transformers (and since there is power going to the board, I'm leaning towards that not being the issue...but I'll test all the voltages first)

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I showed hubs your post, says sorry he isn't more help, sometimes he can say try this or that, but it is hard to tell without looking at it, he says at least you some things to rule out and check on, a lot of people

 

I hope you can get it figured out.

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So I never replaced the controller board...which I think is a good thing

 

I can light the furnace manually, and it works...heats the house...shuts the gas off when it hits the right temp...but the blower still runs forever

 

 

I was patient finally and waited for the furnace to try to cycle...bypassed the safety switch on the cover so I could see more easily, and it tries to light 3 times...and then it flashes once...pauses...then again...then pauses, etc...

 

diagnostic indicates "system lockout"...which simply means (I think) that it tried and failed to light (even though I see the ignitor glowing) and has given up

 

I'm going to have to break down and have someone come out I think unless someone has a suggestion? I could replace the ignitor...they're cheap I think...but I don't want to throw parts at it...

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Did you ever try cleaning the flame sensor? Because this sounds exactly like what ours does and we have to do this like once a season.

 

Good luck!!

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Yep...cleaned it with steel wool...

 

 

funny thing is...when I use the AC, it works...but once it reaches the right temp, the fan keeps going...

 

 

the furnace never lights on its own....

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