Carrier furnace/AC
Product model #58ZAV 075-101JC
Model #58ZAV 075-JC
Series 100
Serial #2093A16 303

Natural Gas/Propane, heat furnace runs on Propane.

Problem: With the unit turned to cooling with the thermostat, the heat pre-purge exhaust fan continues to cycle on and off, sometimes intermittently, most times in quick succession continuously. Turns on, runs for 13 to 15 seconds, turns off and comes right back on, continuing on and on.

The thermost has been tried, replacing with a new, leaving the same condition.

Older thermostat was put back on system, and of course same scenario.

The Main Control Center board was replaced some years ago due to this same mis-functioning and now the conditions have returned.

The exhaust flue and cap are clear and clean. No obstructions found in the furnace or heat box.

The purge fan also continues to run even with the thermostat selected to the off position, with neither heat nor cooling being selected. It also continues to happen with the system running in auto or fan modes, in cooling and heat both.

The only time I can get it to stop is to shut the main breaker to the unit in the main breaker box for the home.

Ideas as to something that may be causing this condition? It's getting rather expensive as the boards run about $300 + installation.

Thank You
LW

Sorry to bring bad news but sounds like the board is defentally acting up again. How long has it been sense it was last changed?

sorry to bring bad news but sounds like the board is defentally acting up again. How long has it been sense it was last changed? Conveniently long enough for the last board that was installed/changed to be out of warranty, but no where near long enough to justify paying the same business another $400+ to change it for me, just to have the false sense of scurity a one years warranty offers. Hell, from the price I found on a new board from a good friend in Kentucky in the biz, I can change out 3 for the price the last one cost to have installed.

sorry to bring bad news but sounds like the board is defentally acting up again. How long has it been sense it was last changed? Conveniently long enough for the last board that was installed/changed to be out of warranty, but no where near long enough to justify paying the same business another $400+ to change it for me, just to have the false sense of scurity a one years warranty offers. Hell, from the price I found on a new board from a good friend in Kentucky in the biz, I can change out 3 for the price the last one cost to have installed.

New board will ship by noon and should be installed by Sat, possibly Friday.

The temporary fix was to open the furnace front doors, unplug the purge fan and let the system cool

Funny and annoying thing about this. Monday morning, while the purge fan/blower was in a continuous looping cycle, we shut the whole system down with the main breakers on the house box.

Turning the juice back on a little after noonish, found the purge blower acting and playing nice, with not once trying to cycle on and off during the 3 hours the ac was cooling and before I un-plugged it's 110 vlt connectors. It must be possessed.:rolleyes: