[majmetro]

Hi there,

12 year old Trane natural gas furnace, Model UD100R9V5J

Furnace sequences through:

1. Draft blower comes up to speed
2. 1st stage pressure switch closes
3. Igniter comes on for 10+ seconds
4. No gas to burners
5. Igniter goes off
6. Sequence repeats

Observations: Flashing LED on circuit board shows flashing slow then flashing fast (calling for heat). I haven't observed any other error flash codes.

I disconnected the leads to the gas valve and ran through the startup sequence above. Used multi-meter and found no 24V DC between the common and Low Fire.

Bad board??

Thanks in advance..

 

[yuri]

You are supposed to get 24 volts AC not DC. No DC controls in furnaces.

If the igniter is glowing then the safeties are proven and it should get power to the valve.

Do you have a gas water heater or other appliances and are they working? If not you may have a problem with your gas meter or regulator.

 

[majmetro]

Dang,

Everything's AC, Okay. Didn't know, just saw the schematic showing 24v.

I'll retest the the gas valve leads..

Yes, gas log lighter, gas hot water is working just fine..

Thanks for tuning in on a Sunday!!

 

[majmetro]

Checked gas valve leads this time looking for AC. Digital multi-meter fluctuates around .05 volts, which I'm surmising nothing is being powered.

Control board part number: CNT 3078

 

[roughneck]

Is there power at the output plug on the board?

 

[majmetro]

Is there power at the output plug on the board?

Not sure what you mean by the board's output plug.

When I tested the power to the gas valve, I examined the wiring from the board to the gas valve's 3 pin connection, which appeared to be in good shape and connected solidly to the control board. I next disconnected the plug at the gas valve and tested for voltage in the connector leading from the board.

Are you suggesting I disconnect the wiring to the gas valve at the control board and test the board's output pins? I guess there's a possible chance one of the connections are corroded or the wiring to the gas valve has a short or is broken. Kinda doubt this, but it's worth a try..

 

[roughneck]

Yes. When tracing an electrical problem, keep backtracking till you can pinpoint the issue. No reason to replace the board if it's something else causing the issue. Be sure before ordering parts.

 

[majmetro]

Checked voltage at board.. nothing. Checked 24V side of transformer at board input --> check good.

 

[majmetro]

Bought a Trane kit 15815 which includes the control board and new igniter (read somewhere igniters may be either 120 volts or 90 volts). Installed kit and everything is working properly.

 

[yuri]

Glad U got it going.:wink2: