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No LED on 350MAV Control Board

4973 Views 32 Replies 7 Participants Last post by  samworkss
I have a 350MAV036060F Bryant Plus 90 furnace whose blower had stopped working and control board LED was flashing 31.
I could cycle the emergency switch to reset but after a couple mins it would shutdown and flash 31 again. Having checked the meaning of code, I performed the following:
1. Checked the vents and intake PVC lines to ensure no blockage.
2. Checked the lines on the pressure switch.
3. Checked the condensate trap.
4. Checked the filter condition.

Not having solved the problem, I saw somewhere online I can test if the blower motor is good by jumping L1 and the blue 'heat' line. When I did that I heard a soft humming sound and the yellow LED went off. Fearing that I had messed up the control board (HK42FZ014), I bought one online and replaced it properly only to find that the LED is still off. I checked the 3A fuse on both old and new boards and it appears good. I used my multimeter and I am getting 120V coming thru the door switch when I tape it shut. I do not get any voltage going to the capacitor and thus no 24V coming out of it. HELP PLEASE!!
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The rollout was not open. I just tried disconnecting/reconnecting it. However I just found the limit switch. I couldn't identify it as a switch because the only visible part is the two terminals. Here's a pic that helped me identify it. The question is how to reset it?
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If it's not resetting on it's own then it needs to be replaced. It has a temperature range printed on it, you need one of the same.
They are inexpensive. Smacking the end sensor can reset it but it's just going to mess up again. Your replacement needs to match the temp setting, overall length and make sure the base will fully cover the furnace probe hole and match the screw positions.
Update. I tried bypassing the limit switch by bridging the 2 wires to see if the blower would work and it did not. I know it worked earlier but now I can't recreate that condition. I am a bit confused by that.
by passing the limit will not cause the blower motor to run.... I am getting confused lol.....:no:
If the limit were open the fan would be blowing cold air.
Guys thanks for your patience with me. So far I have determined that the blower is not running and the limit switch seems to be doing what it was designed to do which is shut the furnace down if the high temp limit is reached. Each time I get a code 33 I power the unit off for about 5 mins and then when I power it back on the inducer motor and burner runs (but no blower) until the limit switch shuts it down and code 33 flashes again. Is there a definitive way to test that the blower motor is ok? Please correct me if I'm wrong in my analysis.
sure...wire the motor direct to line voltage..... :eek::eek::eek:
Sounds like blower is ok , Do you have a wire on cool terminal and heat terminal going to fan motor?Cool usually black and heat blue but doesn't really matter the colors used.
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Common problem with old black CB is bad fan relay problem, which is why new replacment is different board.
Yes. Black to cool and blue to heat.
You were correct. The blower motor is ok. I replaced the run capacitor and all is well again. Thanks to everyone for your expert assistance. The 5uF 370V capacitor cost all of $4.00 and I ended up with an extra control board which I don't mind too mush since I have 2 of the same units in the basement. I still saved money on having to call someone out but the real plus is that I've learned a whole lot!!!
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