Bryant 80 won't fire, no code

Reply

  #1  
Old 12-19-16, 10:20 PM
Member
Thread Starter
Join Date: Dec 2016
Posts: 5
Bryant 80 won't fire, no code

Bryant 80 furnace won't fire. The inducer fan runs, the igniter gets red hot, the gas valve relay engages for about 1 second. As soon as the gas valve relay opens the ignitor goes out. No smell of gas. I measured the voltage to the gas valve, ~25 volts for about 1 second. With the gas valve solenoid disconnected or the switch on the gas valve in the off position I measure 26 volts going to the gas valve for 5 seconds, the ignitor stays red the entire 5 seconds and doesn't go out until the gas valve relay opens. With the gas valve connected and switched on the valve solenoid draws about 220mA measured with a Fluke 88 in series, but only for about 1 second. I can hear the GVR energize and de-energize. I measured the secondary of the transformer with no heat call the voltage is 26.2VAC, when the Gas Valve is energized the voltage only dips down to about 25.5VAC. I can feel the solenoid on the gas valve engaging. It's as if the GVR can't provide enough current to keep the gas valve solenoid energized. That would make sense if it was an SCR or a solid state relay but it appears to be a elctro-mechanical relay. The air pressure switch is made when inducer fan is running, measured 24VAC to ground on both sides. The high limit switch is made, measured 24VAC to ground on both sides. Ground wire from the gas valve is connected to chassis ground.

Any ideas what I'm missing?
 
Sponsored Links
  #2  
Old 12-20-16, 04:39 AM
Member
Thread Starter
Join Date: Dec 2016
Posts: 5
I should also add that the Gas valve was replaced and all measurements and operation is the same with either the original gas valve or the new gas valve.

I also tested the inlet pressure of the gas line by disconnecting the gas valve and connecting a manometer to the incoming gas line where the valve would connect. The gas valve has an inlet test port that's 1/16" and I only have a 1/8" threaded barb for my manometer so I had to disconnect the gas valve to do the test. I read 6.5" w.c. of gas pressure.
 

Last edited by seafur; 12-20-16 at 05:30 AM.
  #3  
Old 12-20-16, 10:21 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 50,580
Likes Received: 108
Welcome to the forums.

If you measure the 24vac with the gas valve disconnected but not when it is connected suggests a defective/arced relay. (bad control board)

Be sure to check the voltage at the board as well in case of a corroded terminal.
 
  #4  
Old 12-27-16, 12:51 PM
Member
Thread Starter
Join Date: Dec 2016
Posts: 5
I tried a new 24V transformer since I had one laying around and that didn't fix the problem. I replaced the GV relay, K5, on the control board, yes I'm "that guy" and that didn't fix the problem. I soldered some test wires on the coil of K5 and measured 13.8VDC while the control board was trying to energize close K5 but that was only for about a second as it did the same thing and opened up almost immediately. The control board in the furnace was a replacement from the previous homeowner and the original control board in unknown condition was left behind. Took a chance and put back in the old control board and the furnace fired up and ran, it's been running for 4 days now with no problem. Only thing I can figure is the 250mA load of the GV solenoid was enough to drag down the DC voltage on the control board to the point of the driver transistor not being able to keep the relay closed. The AC out of the transformer was fine but I never measured the DC voltage on the board while it was trying to energize the GV solenoid. Interesting the micro didn't reset as the power sequence didn't start from the beginning after the GV solenoid attempted to energize. It's working now and it now has a brand new gas valve to boot. I'll keep an eye on the old control board but it's been working for 4 days now and if it fails I'll know what to go after.
 
  #5  
Old 12-27-16, 03:38 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 50,580
Likes Received: 108
We can't help you much with the processing voltages on the board as we have determined that board repair is not a DIY project and that we can only recommend a replacement and no repair.

Usually a voltage sag is caused by a corroded connection or even a defective limit switch as all the power for the board runs thru those switches.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes