# Carrier Furnace - out cold :)



## cheddarhead (Feb 8, 2007)

I have a model 398AAW Plus 90 Carrier furnace. It quit working yesterday - nice and cold day to go out. Well, I thought it might be a transformer problem, so I replaced the 24volt/40watt transformer in the control box. Same problem. The inducer motor spins freely when nudged with a small screw driver. Today I replaced the control board with a new one. Went from a version 015 to a 021 board. Now the furnace will start up, run for a couple seconds then shut off.

What do I do next?


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## #CARRIERMAN (Oct 18, 2006)

Hi cheddarhead

Locate the flame sensor, shut the power off to the furnace. The flame sensor will have a single 1/4" screw in it. Remove the screw use a piece of steel wool, scotch brite pad or a wire brush and clean. Reinstall the flame sensor and see if this fixes your problem.

Good luck
Rusty


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## cheddarhead (Feb 8, 2007)

*Did not see it*

I looked for a single screw device - did not see any... Any tips?
I found a device connected to a circuit board behind the gas valve. Two leads going to that. Removed it and gently brushed it off. No change.


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## #CARRIERMAN (Oct 18, 2006)

Hi cheddarhead

I am sorry, the piece you need to pull out will be a stainless steel rod inside the burner compartment. I should have clarified myself a little better.

Good luck
Rusty


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## cheddarhead (Feb 8, 2007)

*No biggee*

Rusty,
Thanks for the replies... By all means feel free to clarify all you want... I am a bit of a newby to all this...

Is this piece under the spark ignitor access? (see, I am a newby)


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## #CARRIERMAN (Oct 18, 2006)

Hi cheddarhead

Locate the burner box. This is the area with one or two little plastic windows in it, you will normally see flames while the furnace is running in these windows. If you look around the outside of the burner box you will see a piece of procelin with two white wires coming out of it, this is the ignitor. Just opposite of the ignitor will be a porcelin piece with a single white or yellow wire coming off of it, this will be the flame sensor. Please be sure to shut power off to furnace before attempting any kind of a repair.

Good luck
Rusty


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## cheddarhead (Feb 8, 2007)

*This does not look like that*

Hi Rusty!

Well, I took a look for the flame sensor. What you describe is not immediately visible. There is a gas jet for the ignitor, I assume. On that device is a porcelin device like you mention. There is a single RED (big fat red) wire going to it. That wire goes back out to the spark ignitor a bit lower inside. There is another connector there, with three wires. A white, a green, and a yellow. Those wires go back out to the gas valve. There is a component in-line - a diode? a fuse? Could that be an issue?

Tim


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## Brik (Jan 16, 2007)

Time to call the repair man if you are getting cold.


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## cheddarhead (Feb 8, 2007)

Someone suggested replacing the entire gas ignitor / flame sensor assembly. Does thismake sense to you?

BTW - I have secondary heat.. In case Brik wanted to know...


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## jbac (Jan 18, 2007)

yes sir indeed


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## cheddarhead (Feb 8, 2007)

*How to test ignitor...*

Do you know if there is a way to test the ignitor itself? With a multimeter, or voltmeter?


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## #CARRIERMAN (Oct 18, 2006)

Hi cheddarhead 

Sorry I haven't been back to help, I am in the middle of becoming a railroad conductor. Man is this schooling tough. The problem with your furnace is the pilot burner assy. You will need to replace the pilot burner assy if it cannot be cleaned. I would suggest pulling it and cleaning it out. If you have to replace it they are pretty pricy. The part number for your pilot assy. is a LH680005. Sorry it took so long to respond, if you have figured it out already just disreguard this post.

Good luck
Rusty


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## cheddarhead (Feb 8, 2007)

Is there any reason to suspect the ignitor is bad? Is there a way to test that as well? with a multimeter/volt meter?


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## harleyrider (Feb 20, 2007)

Watch the unit as you have someone turn the termostat up, there should be a breif period were you hear the spark box sending a spark to the pilot (TIC TIC TIC TIC ) then the pilot should light. As the pilot burns it heats up a bi-metal strip, the pilot flame itself should be blue and strong. After a period of time the main gas valve should open and all the burners should lite. 

Is any of what I decribed in detail to you taking place?


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## cheddarhead (Feb 8, 2007)

Hey, thanks for the reply. No, there is no snapping sound at all. That is why I asked about the ignitor. The previous post seems to indicate the pilot assembly, but I want a means to verify the ignitor so I do not chase one problem, only to find it is another instead...

The furnace fan turns on, runs for 2 - 3 seconds, then shuts off. I never see a flame of any kind or hear any snapping sound from the ignitor...


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## harleyrider (Feb 20, 2007)

I will do this for you.......if you want to post your phone number i can call you and we can try to figure this out over the phone.


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## cheddarhead (Feb 8, 2007)

Send me an email direct: [email protected]
Once you send me the email I will send you a message with my phone number in it.... Not gonna post my number here.... :no:


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## #CARRIERMAN (Oct 18, 2006)

Hi Ceddarhead

I should have elabirated a little more for you. The three wire pilot on your particular furnace controls the spark generator via the green wire and the main valve via the white wire. This particular pilot burner has a warp switch inside of it that shifts it between pilot and main burner. The switch has a tendency to stick after a period of years. That is why I suggested changing it up but reccomended trying to clean it first due to the expense. Anyway hopefully this information will help you if you still need it, if not it will help somone in the future.

Good luck
Rusty


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## mattTc17 (Nov 8, 2011)

I have a similar furnace, same pilot assembly number I think, printed on it is CG-730PS but all I can find that looks right is LH680005. At the start of winter the pilot was not lighting (ignitor was working though). I took out the assembly, cleaned the pilot orifice, put it back together, and it worked...for awhile. Now the burners are coming on for awhile, long enough for the blower to come on, then after awhile they go out and the blower blows until the air gets cool, burners come back on, repeat. However, this only happens sometimes, sometimes nothing happens at all. Any thoughts? These units don't have main burner flame sensors right? Just the pilot flame sensor? I don't know that these can be cleaned, they seem to be totally sealed. You can remove the ignitor and the pilot orifice but other than that it's all spot welded together.


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## harleyrider (Feb 20, 2007)

is your filter clean, coz it sound to me like your furnace is cycling on the high limit


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## mattTc17 (Nov 8, 2011)

harleyrider said:


> is your filter clean, coz it sound to me like your furnace is cycling on the high limit


Yeah I cleaned the filter a few weeks ago and the unit wasn't run until a few days ago. Is there a way to adjust/clean/replace the limit you're referring to? Maybe it's faulty?

On a related but slightly different topic. Are there repair manuals for different HVAC units like there are cars? I can't seem to find a manual for this thing anywhere.


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## harleyrider (Feb 20, 2007)

with an almost 100 pe off on the high limit. rcent certianty, that furnace is cyclingyou need to do a tempature rise on the unit to detrmine if its a return or supply issue.If you have not been faithfull about keeping the filter cleaned on a regular basis, or if your enviroment is "dirty" you may have a plugged evaporator coil.


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## mattTc17 (Nov 8, 2011)

harleyrider said:


> with an almost 100 pe off on the high limit. rcent certianty, that furnace is cyclingyou need to do a tempature rise on the unit to detrmine if its a return or supply issue.If you have not been faithfull about keeping the filter cleaned on a regular basis, or if your enviroment is "dirty" you may have a plugged evaporator coil.


I have a reminder set up to clean my filter every three months and I've been doing this since I moved into the place. I can't say how good they were about cleaning it before I moved in.

I've been able to get it to work and what seems to be the problem is the pilot either doesn't light or takes awhile to light. I think the cycling is just the thermostat, when I turn it all the way up the burners and blower run continuously without any problems. My suspicion is still a dirty orifice, I'm going to replace that and see how it goes. Next in line will probably be to replace the whole pilot assembly. I'm going to check the control board as well and see how it looks then replace it if it seems questionable.

Maybe I'm just way green, but isn't the evaporator part of the A/C? I'm working on the heater...


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## raylo32 (Nov 25, 2006)

The evap coil is in the airflow typically just downstream of your furnace heat exchanger. What they are saying is that over time the fine passages in the evap coil can get blocked with dust or whatnot. This reduces the overall cfm of the system which may cause the HX to get hot enough to trip a safety.



mattTc17 said:


> Maybe I'm just way green, but isn't the evaporator part of the A/C? I'm working on the heater...


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## mattTc17 (Nov 8, 2011)

raylo32 said:


> The evap coil is in the airflow typically just downstream of your furnace heat exchanger. What they are saying is that over time the fine passages in the evap coil can get blocked with dust or whatnot. This reduces the overall cfm of the system which may cause the HX to get hot enough to trip a safety.


Thanks! With the thermostat all the way up the unit ran for ten minutes before I shut it back off so I don't think it's the limit switch. I will see if that's dirty though as I have noticed the air at the vents doesn't seem to be as strong or hot as I'd expect. I assume you can clean them? Or do they have to be replaced?

Anybody know where a manual for these units or similar is? I can't seem to find one anywhere.


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## raylo32 (Nov 25, 2006)

Cleaning evap coil is a real PITA. I only did mine once in the 15 years it ran before I replaced it. In my case it really wasn't bad and probably didn't really need the cleaning. But some others I have seen pics of here in the forum were quite a mess. They make specific cleaning solutions for the purpose and the passages can be gently brushed out if necessary. Easy to bend the fins so must be very careful.


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## harleyrider (Feb 20, 2007)

mattTc17 said:


> I have a reminder set up to clean my filter every three months and I've been doing this since I moved into the place. I can't say how good they were about cleaning it before I moved in.
> 
> I've been able to get it to work and what seems to be the problem is the pilot either doesn't light or takes awhile to light. I think the cycling is just the thermostat, when I turn it all the way up the burners and blower run continuously without any problems. My suspicion is still a dirty orifice, I'm going to replace that and see how it goes. Next in line will probably be to replace the whole pilot assembly. I'm going to check the control board as well and see how it looks then replace it if it seems questionable.
> 
> Maybe I'm just way green, but isn't the evaporator part of the A/C? I'm working on the heater...


 
sorry for the gobeled post my lap top has a mind of its own sometimes, anyway replacing the 3 wire pilot is inexspensive and easy for a DIY"er. start with that and see if it fixes the problem.......if not then you need to start looking at air flow.


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## mattTc17 (Nov 8, 2011)

Everything seems to be working fine now just from cleaning the orifice. We'll see how long it keeps working.


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## mattTc17 (Nov 8, 2011)

Well that didn't last very long, stopped working again - just never came on last night. I'm assuming the pilot is not lighting, but we'll find out tonight when I have time to look at it. Any tips on getting a pilot to light consistently on these old Carriers?


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## jonesmd (Mar 26, 2012)

*Carrier pilot problem*

Did you ever solve your pilot problem? I have the same issue. Intermittently the pilot will not light even though there is ignition spark. Some times it lights immediately, some times it will spark for two or three minutes before it lights. some times it will spark for ten minutes until it goes into lock out. I have replaced the pilot safety switch and the gas valve.


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## mattTc17 (Nov 8, 2011)

jonesmd said:


> Did you ever solve your pilot problem? I have the same issue. Intermittently the pilot will not light even though there is ignition spark. Some times it lights immediately, some times it will spark for two or three minutes before it lights. some times it will spark for ten minutes until it goes into lock out. I have replaced the pilot safety switch and the gas valve.


Yeah, I just kept cleaning mine and eventually it worked. I'd replaced the aluminum tube last year because I damaged the old one getting it out. I think maybe there were just some specs of aluminum/dirt in the line from cutting it that just kept working themselves into the orifice. Why did you replace the gas valve?


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