American Standard, Flame out, when blower starts

[viper75x]

Model Number

AUD120R960J1

Age

More than 10 years

Hello everyone,
American Standard Freedom 80; year about 2007.
Board: CNT03077

1st Problem: no ignition. Repl. igniter. Worked fine for several weeks.
2nd Problem: no heat. Repl. board, with board CNT06424 from NorthAmericaHVAC.com, which they recommended as an upgrade/replacement. The board came with an igniter.

So the furnace appears to operate through a normal cycle, until minute 1:36. At this point, the flame goes out and the blower motor kicks on. The indicator light flashes red 12 times, which means igniter failure.

Cycle goes like this:

1. Power on
2. LED flashes green - standby
3. draft motor starts
4. i hear 3 clicks
5. igniter lights
6. 1 click
7. Gas lights
8. 1 click
9. i think this is the 1st heat stage.
10. 1 click, then another a few seconds later
11. 2nd heat stage
12. 1 click
13. flame goes out
14. blower on

There may be an extra click in there towards the end, but i am not sure.

Advice?

 

[viper75x]

I have tested both pressure switches by removing them and sucking on the port, with a meter connected. Both have continuity and both open when vacuum is removed. Both close in the operation of the furnace, tested with meter during furnace cycle.

All limit switches are closed before operation and none seem to fail open (tested after flame kicked off and shut power off).

I cleaned the flame sensor, no change. I tried to measure the current in the flame sensor wire, but I cannot determine if there is a change in the current when the flame exists. (Perhaps my meter does not have the precision/accuracy needed.)

I measured the voltage going to the igniter, 110VAC. Which I thought the OG igniter was an 80V and the new was 40V (strange???)

I hope we have some HVAC techs available...

 

[viper75x]

Had an HVAC tech come out yesterday, couldn't determine the cause. He said he had never seen this problem before. So, first thoughts are a bad ground, defective igniter or defective board - both of which are brand new and came together in the appropriate kit.

After poking around later that day I found that the power coming into the furnace is old knob and tube...traced it back around underneath the basement stair case intertwined with a mass of spider webs, and somehow it is on the same circuit as the kitchen lights, some upstairs bedroom lights and a couple of other things! What an electrical nightmare! Needless to say, there was no ground going to the furnace, and whoever installed the furnace should have grounded it, as it was done in 2002 ish.

So, my son and I began replacing the power line to bring in an appropriate ground and put it on a different breaker, with a LOT less power draw (on that circuit). We will finish it tonight and see what happens.

 

[Jake]

Sounds like you found the problem, good job.

Jake

 

[viper75x]

Hopefully!