Put the system in Auto, call for heat, same thing, exhaust fan turns on igniter on, fires, hits high limit, flames go out then blower goes on. Short answer is the board needs to know when to start the timer. Installed all that plus a new 24v transformer. Connect the w and r terminals to see if the issue is furnace or control, next I'd look to see if there is a connection specified on the schematic for gas valve, and how many wires are scheduled to be there. He has been running the system for the last 2 years with the system in "FAN ON" mode instead of auto. With all that said my attempt to repair was to replace the main board and since the blower motor was making noise and going bad I replaced that too. Also look for blower to start immediately when limit is tripped which is a common attribute for most controls. Different manufacturers accomplish this from 2 main methods, internal to the board, or external. Is there a possibilty that the gas valve controls the blower on after it calls for heat? Ill try to download and review the schematic to see if I can find any more details that may be helpful. Blower timers are sometimes set for 90 sec or more so check to see what the blower timer is set for, and time the burner run time from ignition to limit cut out. Armstrong Ultra SX-80- Vintage 1996 Let me explain- Furnace calls for heat, system goes on triggers the exhaust fan, igniter lights, flames come on 30 seconds later the blower is suppose to turn on but does not turn on until the high limit triggers. I am trying to fix a furnace for my neighbor, problem seems very obvious but hit a couple bumps. I havent measured there yet to see if that is working, that is probably the culprit. The Delay on is set to 30 seconds The delay off is set to 140 seconds, both are default settings I have tried the others From what i have found the gas valve has a terminal for EFT electronic fan timer that is supposed to energize when the gas valve opens and de-energizes when the gas valve closes. To add to the clues, I was told the gas valve was changed out for some reason a few years back but I could not identify if the existing valve was the exact replacement or not. The gas valve appears to be functioning properly but I am thinking it may not be the exact replacement losing that function.。
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