Gas pack blower fan won't shut off, replaced fan board

[jesandor]

So a local hvac company came out and diagnosed my fan control board as being bad. My gas pack indoor fan and combustion fan kick on as soon as I send power to the unit. I replaced the board with a new Honeywell st9120u (the new board) and it did the same exact same thing. I'm racking my brain as to what else could be causing this to happen. I find it hard to believe that the new board could have the same exact problem the old board had. We were able to bypass the board and call for heat to fire up. Really thought the new board would fix this problem. Any help would be appreciated. The unit is a comfortmaker gas pack PGAA36E1K7.

[rglasgow]

You might callback the company who diagnosed the board as bad. Should not be too difficult with a meter and the proper know how.

[jesandor]

Yeah i ordered and installed myself based on diagnosis. I would find it statistically difficult that a brand new board would have the same exact issue as the old one.

Is it possible there is a bad limit switch? I noticed on the wiring diagram there is a rollout switch and a limit switch. I've heard of these being faulty and causing this same issue?

[SBKold]

Wait a sec.

Did you order and install the board yourself?

Maybe third ones a charm.

[rglasgow]

About a month ago I came across a furnace whose board would not turn blower on in heating mode. With a meter I diagnosed as a board issue and replaced. Furnace doing same thing with new board. Pulled out meter, rechecked everything, reread INSTALLATION manual for any changes. Installed third board and works fine.
MORAL is you need a meter AND the proper knowledge to diagnose and not just change parts until it works.

[jesandor]

troubleshooted using the LED and it threw a fault for an open limit switch. checked both switches and the rollout switch was stuck. Fired everything up and worked fine, but the rollout switch has tripped again. is it possible the switch needs replaced or something else causing this issue? the tech noted that if the heat exchanger was cracked that my CO detector would be picking it up, so he didn't suspect that as a problem.

[hvacvegas]

troubleshooted using the LED and it threw a fault for an open limit switch. checked both switches and the rollout switch was stuck. Fired everything up and worked fine, but the rollout switch has tripped again. is it possible the switch needs replaced or something else causing this issue?

It's possible that they would have replaced the board, found the new issue, and gave you back your money on the board.

Instead you decided to do it yourself.

Anythings possible.

[jesandor]

the board was cheap, so I'm not upset about that. i'm just curious why the rollout switch continues to trip. i know from experience that this can be a serious issue. has anyone heard of rollout switches failing over time? the unit is about 10 years old and the switch is above the burner where some rust has accumulated.

[SBKold]

Did you find your tech on craigslist? That's horrible advice.

[beenthere]

Your gas pack has problems. Probably a cracked heat exchanger. Stop using until its verified safe, or replaced.

[rglasgow]

Bad heat exchanger will not always set off CO detectors. Time to find a professional to inspect your unit.

[jtrammel]

Get another company to come inspect heat exchanger, I think you got "pony" the first time.

[rglasgow]

I have not heard from "pony" as of late. Is he still with us?