Carrier 58TUA - LED code 34. No flame. Ignitor doesn't glow but measures 90 ohms.

I don't expect the thermostat since I'm getting the code 34. Cleaned flame sensor even though the ignitor isn't glowing. If I disconnect the ignitor can I measure for voltage? Or will the little bugger not engage the relay with the ignitor disconnected?

I also suspect the ignitor relay but it's soldered on the control board and the control board is very hard to access. From what I can see I would have to bypass the cabinet door switch and have the control board completely apart. Not sure that's a good idea...

Any thoughts would be appreciated.

-Neil

 

Welcome to the forums.

Yes.... you can disconnect the igniter and check for 120vac.
90 ohms is close to the max resistance on most igniters.

 

Thanks Pjmax!

I just ran through a startup with my DVM set to AC on the ignitor contacts - ignitor disconnected. On startup I saw 3VAC (induction, possibly?) which after its 90s statup rose to 5VAC then to 7VAC at which point the indicator LED changed from no fault to code 34, same as when I had the ignitor connected.

I'm not sure if the three different voltages were all induction. Either way it's low enough for me to think it's stray voltages. I can try to order the ignitor relay but but I'm not sure I'll find one.

 

You would see the full 120vac present there if it was there.

There are no parts considered replaceable on the control board.
The control board is replaced as one complete and tested unit.

That being said.... what you do on the side is up to you and the relays can be found at electronics parts distributors if you look.

 

Found the relay at Mouser. Gave me an excuse to order the parts to repair an amp that's been on my bench for six months.

The relays aren't easily replaced with an iron and wick but I have a desoldering iron that will make short work of it. Fingers crossed that the relay is the problem...

Thanks for your help!

 

Mouser is the ideal place and is where I get most of my parts like that.

 

So the relay arrived and it was easy to replace. Unfortunately it did not solve my problem. I can't seem to find any obvious issue (cooked resistor, bad diode). I'm worried that it's the microcontroller. I've looked online and here in Canada, a replacement will be pricey. Time to call a local to come look at the furnace.