Carrier furnace lockout question

[tlb]

Have Carrier furnace mod#58MXA100-F-1--16 ser#0503A10693.It is twinned.Was doing scheduled service and found the left furnace locking out on code "13",which is limit circuit lockout.Check limit circuit at board where it goes into plug adapter.Circuit was closed.Also the 13 code is only supposed to show if the limit circuit is open for more than 3min.If the limit opens it is supposed to give a 34 code until the 3min has elapsed and then switch to the 13.This furnace would not give 34 but go straight to 13 in less than the 3 min.I assumed board was bad,replaced but same thing happened.I checked the limit circuit multiple times I am sure it is closed.Any help would be appreciated.

[jbooker56]

I only found a poor wiring diagram but it looks like there is a resetable flame roll out switch in the limit circuit.

[tlb]

Yes,there is a manual reset rollout and a auto reset hi limit in the circuit.Again I have checked the limit circuit at the control board multiple times and it reads closed.Also I forgot to mention the furnace locks out before it even fires.

[jbooker56]

I feel bad that I have nothing for you. In the back of my mind I am almost sure I have had the same thing before and I would love 10 minutes with the furnace. please let me know when you beat it'

[pauls heating &]

if im not mistaken unless you have the old origional board as a replacement..
in twinned applications both boards must be replaced w the new upgraded mxa board
conversion kits

[jbooker56]

Probably too late but I ran into basically the same problem on a bryant furnace with similar board. Limit and reset checked out but still had code 13. Found the problem was in the exhaust system with pressure switch not making which explained why the code came before any heating. It must be a hitch in the board which is why it seemed familiar.

[tlb]

jBooker56 you were right.Checked draft switch with inducer running and it was open.Disassembled venter and got to excavate 4 birds out of the vent pipe.Put back together and worked fine.Crazy why it was giving the 13 code.Thanks for the replies.