Ask Me Help Desk - Gas furnace

Hope someone out there can help, because it's going to get cold this weekend!

I have a split HVAC unit with furnace in attic. Written on front of unit is Intertherm. Inside panel of unit says Nordyne, and the Ignition Control is Robert Shaw. The unit is 13 years old and the heat worked fine last year. Here's what happens (or doesn't happen.)
I turn on heat and everything sounds normal... except blower doesn't start. I go upstairs and notice the coil glows for a few seconds then goes out for about 15 seconds. This sequence repeats 2 more times. The unit will run for a long time before I finally turn it off. The flame never comes on. Also, if it matters, the blower works in the -on- position.
Afer much surfing, I even cleaned the sensor coil and also checked for loose connections.
Please advise so I can have an informed idea before I make the dreaded service call!!

Thanks in advance for you time!

Quote:

Originally Posted by diygirl

Hope someone out there can help, cos it's going to get cold this weekend!

I have a split HVAC unit with furnace in attic. Written on front of unit is Intertherm. Inside panel of unit says Nordyne, and the Ignition Control is Robert Shaw. The unit is 13 years old and the heat worked fine last year. Here's what happens (or doesn't happen.)
I turn on heat and everything sounds normal...except blower doesn't start. I go upstairs and notice the coil glows for a few seconds then goes out for about 15 seconds. This sequence repeats 2 more times. The unit will run for a long time before I finally turn it off. The flame never comes on. Also, if it matters, the blower works in the -on- position.
Afer much surfing, I even cleaned the sensor coil and also checked for loose connections.
Please advise so I can have an informed idea before I make the dreaded service call!!!

Thanks in advance for you time!

Member "Northern Heat" will be along soon to fix you up. He is the only one I know who can for sure troubleshoot this complicated problem for you. Hang tight...

I think the gas valve should open a timed delay after the ignition. You might be able to hear it or feel it if you have your hand on it. If it isn't opening, check for 24 volts AC on the terminals. If it has power, and no flame, it is bad.

If no power, something on the board may be bad. I replaced the board on my furnace, $$$$$$$$. Not sure if I could the gas valve.

Nordyne used several different safties in series with the gas valve. It can be a pressure switch not closing or a roll out limit that tripped. You are going to have to test for voltage to the gas valve. Start at the PC board and follow the wires all the way to the gas valve. After the ignitor starts to glow the board only sends voltage to the valve for about 10 seconds, after the 3rd time it will lock out and you will have to turn the furnace off and on again to reset it. If your lucky it's a roll out limmit, just push the little button between the 2 wires that connect to it. You will hear a small click from the board after the ignitor glows sending voltage through the on-board relay to the gas valve, if there is not 24 volts from the board after that click or no click the board is probably bad. Sorry best I can do from here.

Quote:

Originally Posted by rickdb1

Member "Northern Heat" will be along soon to fix you up. He is the only one I know who can for sure troubleshoot this complicated problem for you. Hang tight...

I had a similar problem last year.It turned out to be a bad Thermocouple.The thermocouple is a temperature sensor for want of a better word.This has to be satisfied temp wise before the main burner will come on.