I am a HVAC contractor looking for anyone who may have seen this issue before. I was on a service call today for a bryant 80plus 395CAV and the control board was showing error 31 pressure draft safegaurd/ Aux Limit.
Of course this could be a potential problem with either the draft fan,pressure switch or aux limit but all checked ok. Aux limit was not tripped and was closed. Inducer runs and operates correctly. Pressure switch shows open when inducer is off and closed when inducer runs. I checked voltage on the common side of the draft switch and monitored to make sure the draft switch was not droping out while inducer was running and found everything to check fine.I noticed a few things that seemed odd to me. (1) Ignitor would still energize when control board showed 31. (2) when checking common side of pressure switch to ground on initial start of the draft fan,I removed my test leads and the furnace would suddenly shut down almost as if there was a power bump. (VERY ODD). I checked the molex connector at the board and it looked fine didnt see any obvious issues. I consider myself to be very competent and I always refuse to randomly change parts and fix thru process of elimination but Im leaning towards replacing the conrol board and my questions are:
(1) Could this be some sort of intermitent faulty ground issue ?
(2) Has anyone seen anything like this before (a known issue with this board)?
(3) I have never seen ignitor energize when showing draft or aux limit failure, ignition sequence should never start. What do you think? Curious to know.