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No LED on 350MAV Control Board

4968 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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Thanks for replying. Yes I meant transformer and I measured 120V to neutral.
Let me go double check my wiring. I'll be right back.
You guys were correct about the connections! I had the L1 wire connected to COOL and vice versa. Now I'm back to where the LED is solid and everything except the blower runs then shuts down with 33 this time.
It says Limit Switch Lockout - Check for dirty air filter, check fro blocked return-air or supply grilles.
My filter is new and as far as I can tell there's nothing blocking the air intake, but I'll get a flexible wire and probe it again. What else can I check?
OK I'll go check the limit in the blower compartment.
Well the old one was pretty dirty, so that's a possibility. I couldn't find the limit switch in the blower compartment. Is it the same as the rollout switch?
There's a rollout switch on the burner compartment which is not tripped, but other than that there doesn't seem to be a limit switch for my model. I see one in the diagram for the 355MAV but not the 350MAV.
Well guys I only found the rollover switch with 2 red wires and decided to disconnect them and turn the system on. Lo and behold the blower came on and ran. Feeling brave I reconnected the red wires to the rollout switch and again powered up the furnace. This time the blower came on and everything ran for about 2-3 mins before shutting down again with 33. Now at least I know that the blower is ok.
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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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.
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.
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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