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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Heat and fan lights flashing and no heat

Customer Question

Heat and fan lights flashing and no heat
Submitted: 1 year ago.
Category: HVAC
Expert:  BillyHvac replied 1 year ago.


is the light on the circuit board in bottom of furnace solid or blinking?

Customer: replied 1 year ago.
I don'e see any lights on at all
Expert:  BillyHvac replied 1 year ago.

see page 10 HERE

do you see this circuit board in bottom?

Expert:  BillyHvac replied 1 year ago.

I apologize as I am not currently configured for phone call. I will transfer you


Customer: replied 1 year ago.
Thank you. Hopefully soon? I am somewhat cold!
Expert:  Phil replied 1 year ago.


These fixes are not always fixable in short order, it can take a day or two to get parts, and depending on what I can do here and what your skill level is, you may have to call in a local HVAC repair company.

Please attach a well focused, close up photo of the wiring diagram glued inside the service panel,you can use the paper clip icon at the right end of the toolbar at the top of this dialog box,Include a picture of the thermostat wire connections to the printed circuit board in the same area.

If there is no paper clip icon, look for the '+attach files' link at left of your send button.

I can mark it up with trouble shooting instructions. You will need a multi meter ($30 at a hardware store) and some experience working with appliances, let me know a lot about your skill sets in those regards.

We can go from there.

Customer: replied 1 year ago.
Attached. Also I had requested a phone call. Do I need to do that again?
Customer: replied 1 year ago.
Did you get the photos?
Expert:  Phil replied 1 year ago.


Notice however that photo is taken at an angle and that the legend on the lower left is not readable, it will help a lot if you can follow up with a straight on photo, try to eliminate that glare spot if you can, it can block out part of the diagram if you change the angle.


Use a hair drier to slowly and gently warm the card to 120F(warm to the touch but not hot and not over140F)... if you get any change in behavior that means the card is bad...

A micro crack has opened in the printed circuit at a solder joint, or inside its CPU in that case .... or a short circuit has developed as the card expanded when you heated it.

Constant expansion and contraction as these electronics heat and during their duty cycles over the years is what wears these cards out.

It is also a good idea to replug all of the connections in the unit,that burnishes any oxidized terminal connections and will sometimes solve the problem, especially at the printed circuit card and in any sensor molex connectors. Do that with the power off to the unit of course.

We can go from there.

Expert:  Phil replied 1 year ago.

I only got the wiring diagram photo,

Customer: replied 1 year ago.
More photos attached.
It's currently 57 in my house. Is s phone call going to be more efficient?
Expert:  Phil replied 1 year ago.

Hello again, if you are on a cell phone, with your multi meter in one hand and your cell phone in the other hand and talking to me live as you do the tests I ask for, that will work... if not this dialog box allows for the diagram exchanges I need to coach you effectively.

If the pictures of the legend are not on the same picture as the wiring diagram, I have to fill my screen with both, and toggle back and forth between the two, and that leaves me no room to type in my dialog box... an all in one photo is best, ***** ***** needs to be from straight on...your focus is superb however, thats for that.

A phone call will not help a lot, and gives you no time to find points I need tested,

Customer: replied 1 year ago.
I took the door off and laid it fkat for the photo.
I don't have a multi meter. Do I need to get one?
Expert:  Phil replied 1 year ago.

That is perfect, thanks.

You need a 'self ranging multi meter' and some practice using it.

Customer: replied 1 year ago.
Not sure that does me any good. If I can pick one up at some point I can recontact you but have to leave house now for other business.
Expert:  Phil replied 1 year ago.

Hello again, you can log off, shut down your computer and leave the house.... then later simply log back into your JA account, click on your question and resume the conversation.