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Scott
Scott, HVAC Technician
Category: HVAC
Satisfied Customers: 398
Experience:  30 yrs. experience as self-employed HVAC Service Technician. Universal EPA Certification, NATE Certified, Trane Service One, ACCA ACE Certified.
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Furnace model number 398aaw036060d. Furnace fan kicks in but

Customer Question

Furnace model number 398aaw036060d. Furnace fan kicks in but the burner doesn't come on, not even the pilot. Fan also runs constantly.
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

Does the little vent motor come on or just main blower?

Customer: replied 1 year ago.
Just the main blower
Customer: replied 1 year ago.
At least, I think it's just the main blower.
Expert:  airheatman replied 1 year ago.

Ok these units were made in mid 1980s before they started putting the boards on them with error lights to help us in troubleshooting so it is going to be a process of elimination to determine issue. First thing I would check is limit switches. Start with the resettable ones. Look near burners, draft hood and on blower housing (Bryant used them in various locations on these furnaces. to see if there is one tripped. If so, the little button inside will push in to reset it. We will go from here. See link below for an idea of what I am talhttp://www.repairclinic.com/PartDetail/Limit-Switch/HH18HA195/2347657?ss=-x333938616177&mr=1king about.

Customer: replied 1 year ago.
I can't find a single switch like the one in your link.
Customer: replied 1 year ago.
The fan control center was replaced a couple weeks ago, in case that helps narrow things down.
Expert:  airheatman replied 1 year ago.

Lets check those limits first.Usually the limit will cause blower to run nonstop and no heat.If none like I sent we will check the main limit .

Customer: replied 1 year ago.
I can't find anything with a pushable button.
Expert:  airheatman replied 1 year ago.

OK Do you know where the main limit is?

Customer: replied 1 year ago.
I know where it is, yes
Expert:  airheatman replied 1 year ago.

Lest just for a test, bypass it to see if we can get burners to come on. You can do this with a jumper wire, a fuse or a straightened paperclip or something.

http://i.imgur.com/Aqd9O0f.png

http://i.imgur.com/WqmGzzO.png

Customer: replied 1 year ago.
Tried it with a paper clip, no flame.
Expert:  airheatman replied 1 year ago.

Turn power off so board will reset and then back on with the switch bypassed and see if same results.

Customer: replied 1 year ago.
Still no flame.
Expert:  airheatman replied 1 year ago.

Was trying to locate a wiring diagram, Usually there are at least one or two of those resettables ones in the limit circuit.Usually can find them by tracing the wires from the main limit.

Customer: replied 1 year ago.
As far as I can tell, the wires go from the main limit to the control center, nothing in between.
Expert:  airheatman replied 1 year ago.

Does your unit have a small vent motor and if so does it come on?

Customer: replied 1 year ago.
it has a "draft inducer" motor and it doesn't come on.
Expert:  airheatman replied 1 year ago.

Ahh, Nothing else will work until it comes on and closed pressure switch by vaccuum. Check and see if we are getting power to that motor.

Customer: replied 1 year ago.
How?
Expert:  airheatman replied 1 year ago.

Do you have a volt meter?

Customer: replied 1 year ago.
No
Expert:  airheatman replied 1 year ago.

You would need a meter to check. You can get an inexpensive one at Lowes for about 20 bucks if you want to get. Then unplug wires from inducer and see if we are getting power on call for heat. Can you turn the wheel freely?

Customer: replied 1 year ago.
Wheel turns freely
Expert:  airheatman replied 1 year ago.

Next step I to determine if we are getting power to it. Do you want to get a meter and continue tomorrow?

Customer: replied 1 year ago.
I will pick up a meter but will have to continue on Wednesday
Expert:  airheatman replied 1 year ago.

Sounds good, Also if there is a wiring diagram on unit if you can take a picture and paste it here will help me guide you, I have not found the wiring diagram.

Expert:  airheatman replied 1 year ago.

Leaving for the night.Look forward to continuing on Wednesday

Customer: replied 1 year ago.
I had to take multiple photos because the print is so small but that's the diagram on the furnace.
Expert:  airheatman replied 1 year ago.

Thanks. Do you have the volt meter now?

Customer: replied 1 year ago.
Expert:  airheatman replied 1 year ago.

OK lets unplug the wires at the vent motor, Turn power off to furnace and then back on. Call for heat at thermostat and check to see if we are getting 120 volts at the connector you unplugged from vent motor

Customer: replied 1 year ago.
I'm not getting a reading
Expert:  airheatman replied 1 year ago.

OK lets do this. Unplug those plastic 7 pin connectors, look and make sure pins are seated in connector good so they make contact with boards and then plug back in

Customer: replied 1 year ago.
Done
Expert:  airheatman replied 1 year ago.

Did that make a difference?

Customer: replied 1 year ago.
No
Expert:  airheatman replied 1 year ago.

Based on what we have done, I am suspecting board but hate to condemn board without being there. I can open this to other experts who may have more ideas if you would like.

Customer: replied 1 year ago.
Would that be the board that I just replaced or is there another one?
Expert:  airheatman replied 1 year ago.

Yes the main board. Was it doing this same thing before you replaced the board?

Customer: replied 1 year ago.
Last time the fan ran constantly regardless of what the thermostat was set to, but the heat and a/c came on correctly.
Expert:  airheatman replied 1 year ago.

Wow, The newer furnaces have a light that flashes a given number of times to indicate the problem, These older ones often required trial and error .I hate telling you board is issue without being there, so let me open this to other experts to see if they have ideas.

Customer: replied 1 year ago.
Ok, thank you.
Expert:  airheatman replied 1 year ago.

Thanks for allowing me to work with you to this point.I have opted out of the question to see if perhaps other experts may have more information and can assist.Please do not rate or reply as that will send question back to my desk.Please stand by to see if another expert can assist further.

Expert:  BillyHvac replied 1 year ago.

hello, are you available now?

Customer: replied 1 year ago.
I am
Expert:  BillyHvac replied 1 year ago.

on the circuit board..locate SEC1 and SEC2..use meter to test those 2 terminals. tell me result...make sure and test meter in an outlet to make sure it reads power correctly

Customer: replied 1 year ago.
Just to make sure I'm doing this right, I've been checking it as AC, should I be checking as DC?
Expert:  BillyHvac replied 1 year ago.

AC ~ volts. That is why I like testing an outlet. If it reads 115-125 volts we are set right.

In this case we are looking for low voltage of 24v

Customer: replied 1 year ago.
I'm not getting a reading on either of the terminals but the outlet tests correctly.
Expert:  BillyHvac replied 1 year ago.

Thank you,

you have a bad 24v transformer.

To confirm...is power on to furnace?

Is door pop out safety switch taped down (if present)

Does L1 and L2 show 120v?

Customer: replied 1 year ago.
Safety switch is now taped down, SEC 1 reads ~27, SEC 2 doesn't read.
Expert:  BillyHvac replied 1 year ago.

Now thermostat wire terminals on circuit board...Terminal C with black meter lead and terminal R with red meter lead

Customer: replied 1 year ago.
No reading with thermostat terminals, L1 reads ~120, L2 doesn't read
Expert:  BillyHvac replied 1 year ago.

ok,

now..the limit on front wall of furnace...size of credit card with 2 wires attached..do you see this?

Customer: replied 1 year ago.
I see it.
Expert:  BillyHvac replied 1 year ago.

still with power on...black meter lead to any metal cabinet part..red lead on terminal of limit..and then other terminal.

Or..put the mter leads one lead on each terminal at same time...tell me result

Customer: replied 1 year ago.
No reading
Expert:  BillyHvac replied 1 year ago.

on either test?

Customer: replied 1 year ago.
Not on either test
Expert:  BillyHvac replied 1 year ago.

This may seem strange but bear with me..

1st - take handle of screwdriver and rap the side of the pilot assembly.

2nd - take a picture of the wires going to pilot and post...some of these units had a fusible link in the yellow wire to pilot

Customer: replied 1 year ago.
Done and done.
Expert:  BillyHvac replied 1 year ago.

can you please pop the front burner off?

Customer: replied 1 year ago.
Did you mean the cover? If so, here you go. If not, please clarify :)
Expert:  BillyHvac replied 1 year ago.

ok, see the yellow wire in burner section with burned fusible link?

Customer: replied 1 year ago.
Yep
Expert:  BillyHvac replied 1 year ago.

we want to cut that out and wire yellow wire direct.

We also want to get a shop vacuum and clean out the soot in the compartment...is this propane or natural gas?

Customer: replied 1 year ago.
Natural gas - we just bought the house and first time opening this up, thanks.
Expert:  BillyHvac replied 1 year ago.

Ok, give the unit a good vauum, make sure the pipes are clear...fix that wire..and your back in business.

Billy

Customer: replied 1 year ago.
Vacuumed the unit but I don't know if there's enough length to cut out the link and wire together.
Expert:  BillyHvac replied 1 year ago.

You can patch in a length of different wire. It is not pretty...but it will do the job. They stopped using this fuse after a couple of years and did away with them...

wire nut a wire below the box..run into box and wire nut to wire.

Customer: replied 1 year ago.
K, is there a special type of wire to be used since it goes into the burner area?
Expert:  BillyHvac replied 1 year ago.

no, just a standard 18 gauge wire will even do..if there is an extra thermostat wire I would use a piece of that. In theory, the box has fresh air entering from intake pipe..the heat should only be in front of burner. That is why we want the pipes clear.

Expert:  BillyHvac replied 1 year ago.

I apologize but I must go offline now. If all set just rate service..if you have more questions I will respond tomorrow

Billy

Customer: replied 1 year ago.
Ok, will have to try this tomorrow. Thanks a lot for your help, will let you know how it goes.
Expert:  BillyHvac replied 1 year ago.

any good news today?

Customer: replied 1 year ago.
Put the patch in, but did not fix problem. Fan still runs constantly and heat does not kick in
Expert:  BillyHvac replied 1 year ago.

on your new circuit board...is there a blade fuse like found in a car...purple with a 3 or yellow with a 5?

Customer: replied 1 year ago.
Purple with a 3
Expert:  BillyHvac replied 1 year ago.

can you tell if good?...or...remove fuse...power on door switch taped..meter lead on each fuse terminal..tell me result

Customer: replied 1 year ago.
Meter result 20
Expert:  BillyHvac replied 1 year ago.

can you show me a pic of side of fuse?

Customer: replied 1 year ago.
This way?
Expert:  BillyHvac replied 1 year ago.

does it appear the filament is intact?

And now that pilot wire fixed...what is reading of C to R again?

Customer: replied 1 year ago.
The filament is intact, C to R reads 0
Expert:  BillyHvac replied 1 year ago.

ok the edge connector on the circuit board where all the wires attach.....remove the connector and inspect the slot...any hot spots?

And do you have a spark box where cable plugs in that is a 2x3 or more like 4x6?...or a box called a lockout timer?

Customer: replied 1 year ago.
I don't see any problems with the connector on the circuit board. There's a black box that says spark igniter, is that what you're looking for?
Expert:  BillyHvac replied 1 year ago.

yes..is it small like 2x3 or larger like 4x6?

Customer: replied 1 year ago.
Smaller
Expert:  BillyHvac replied 1 year ago.

well we are at the end...the smaller board at the pressure switch..or the pressure switch itself.

test the orange wire at the pressure switch and tell me reading

Customer: replied 1 year ago.
No reading at the pressure switch.
Expert:  BillyHvac replied 1 year ago.

ok,

power at sec1

no power at R

no power at orange wire for pressure switch

This means the glitch is in the harness or the small board behind the pressure switch. Can you remove and look at back of the small board?....the breach is this board or the harness

Customer: replied 1 year ago.
I'm looking at the back of the small board
Expert:  BillyHvac replied 1 year ago.

this is known as the inducer board

Customer: replied 1 year ago.
ok
Customer: replied 1 year ago.
Did something happen?
Expert:  Scott replied 1 year ago.

Hi this is Scott,

I have read through the conversations on your question. I am curious of one thing at the point where you jumped the main limit is there a resistor looking thing with a female spade terminal on it? Also Billy mentioned the small inducer board have you removed the screw and wire plug and inspected the back of that circuit card?

Customer: replied 1 year ago.
Here are photos of the main limit pulled out as well as the back of inducer board.
Customer: replied 1 year ago.
The inducer photo didn't load, here it is.