Good afternoon all,

My question is in regards to the Bryant 373LAV Downflow/Horizontal gas furnace. A good friend of mine called for my help because about a month ago, her furnace blower randomly began running all the time and the only way she could shut it off was to flip the breaker on the furnace. She was told that her control board (the CESO1100-57-00) was bad and needed to be replaced. She ordered a replacement board (the ICM281) which I installed for her last night but the problem still remained. After replacing the board, I flipped the breaker and sure enough, about 10-15 seconds later, the blower started up again.

I have been doing some research for her to see if I could resolve this problem and have seen references to the Limit Switch and Fan relay, with the possible cause being the Limit got stuck open. I assume (but am probably wrong) that the fan relay is located on the board, so the replacement would have taken care of that if it were the problem? Also, the blower starts even when the thermostat is disconnected. I'm not sure of the model Thermostat she has, but it is a battery powered one that can be taken off the wall, to reveal a number of colored wires that are screwed in to the back panel of the thermostat. So with this being said, I'm assuming it isn't the thermostat either, which leads all back to the Limit being stuck open? I have the User information Manual for this model of furnace and see on the Furnace component legend that there is a "Manual-Reset Auxiliary Limit Switch" listed as (when used) and also a Manual Reset Limit switch with (2) listed after it.

I guess I wanted to ask if I am on the right track and if anyone has any tips/tricks/suggestions regarding this type of problem before I went further poking around in the furnace and cause possible damage to the unit, myself or my friend's house.

I thank you all for your assistance and if I'm leaving any information out, please let me know as summer is coming up and I'm sure she'd love to be able to use her A/C w/o having to go in and out to her Fuse box every time.

with the possible cause being the Limit got stuck open

This could cause the problem. When the limit is tripped it causes the blower to run all the time since a tripped limit is a indication of a furnace overheat prblem.

It could also be a crossed or shorted thermostat wire. The way to test that is to remove the G wire in the furnace from the terminal strip OR you could remove all the wires from the terminal strip. With wire/wires removed the blower should not run.

with the possible cause being the Limit got stuck open

This could cause the problem. When the limit is tripped it causes the blower to run all the time since a tripped limit is a indication of a furnace overheat prblem.

It could also be a crossed or shorted thermostat wire. The way to test that is to remove the G wire in the furnace from the terminal strip OR you could remove all the wires from the terminal strip. With wire/wires removed the blower should not run.

Thank you very much for your quick reply!

If the limit was tripped, how should I go about resetting it?
Going off the legend on page 3 of the following manual I would assume that the listed Reset Limit switch(es) are buttons? Dials? Screws? http://www.gogeisel.com/geiselonline/support/Bryant/373LAV_376CAV_383KAV_395CAV_Gas_OM.pdf
Also, what could cause possible overheats? Hot days? Dirty Filters? (I just want to get as much info as I can to pass it along so it doesn't happen again.)

And as for the possible shorted thermostat wire, when you says remove the G wire from the terminal strip, are you referring to the screws on the control board (as showed on the bottom of this PDF http://icmcontrols.com/downloads/ICM281-fcl.pdf )?

And as for the possible shorted thermostat wire, when you says remove the G wire from the terminal strip, (Yes this is where the G wire lands).

On the other link look for number 12 manual reset for upflow and number 11 and 2 for horozontal or downflow. Should be a small red button in the center.

Thanks again for the follow up.
I will check this out and get back to you.


Cheers!

I got a chance to check out the furnace again today and found 3 limit switches and pressed them all. That didn't seem to solve the problem either. I then unhooked the wire from the G terminal and the motor still kicked on when the power was restored. Any thoughts? Thanks again for your help, by the way. It is very much appreciated.

It is possible the replacement board was wired incorrectly.

It is possible the replacement board is defective BUT if new that is usually not the case.

Test the limit switches. Just pressing the button does not mean they are good. Usually the button will pop out when tripped BUT a test with a meter or jumper will tell the true tail.

Service manual here

http://www.docs.hvacpartners.com/idc/groups/public/documents/techlit/sp04-62.pdf

How many blinks or codes does the board show. Usually if there is a fault the board will blink.

Did you follow the directions EXACTLY for the new board? Did you do a test on the new board as described in the directions below? Did the test show any problems? Is the polarity correct for the 120 volts applied to the board? It has polarity protection as described in the instructions BUT it still needs to be correct.

Is the board grounded correctly?

Did you notice and water damage on the old board?

SEE the directions here

http://www.icmcontrols.com/downloads/icm281_ag.pdf

The blower motor is controlled by this board so something is wired wrong.

Did you disconnect the G wire on the circuit board as requested in a previous post? This will tell us if the thermostat wiring is causing the problem. You did not post back with those test results about disconnecting the G wire from the board.

Every time you test something if the blower does come on give it a minute or two to turn off as there is a built in time delay on this board and you may think the blower is running because of a problem when it is just the time delay function.

Post back with results.

Hi HVAC 1000,
I am having the same problem today. Blower would not shut off last night, had to remove the front panel so the safety switch would shut it down. I followed your tests, removing the G wire and then all thermostat wires did not shut down the blower. I pressed the reset buttons on 4 different limit switches and the blower still runs. The LED code is 33 and remains 33, did not go to 13. Can't afford a technician, have to figure it out myself. Please help me if you can. Thank you, Jerry