Trane Furnace / White Rodgers Controller

[coopsterj]

I have a Trane Furnace Mod# TDE100AN45K0, with a White Rodgers controller Mod# 50A50-571.  The furnace will not come on, when heat is called for.  The indicator light on controller flashes 2 times, indicating "System lockout, no flame.  Check line polarity".  When heat is called for, the fans start up, and gas flows, however the ignitor won't light.  There hasn't been any work done on the system, and it worked last winter.  I'm assuming the controller has failed.  Looking on-line, there is a universal replacement, White Rodgers Mod# 50A55-843.  The picture looks considerably different than the 50A50-571.  First question, is this the right assumption, and if so, is this an easy switchout?  Or should I be looking somewhere else.  Any help is much appreciated.

[JWWebster]

If you getting a lockout that means the control ain't getting back a confirmation of ignition. You either have a bad ignitor , a dirty flame sensor, or a rollout switch popped due to some sort of air restriction or a partially clogged proving switch tubing. I came across a high efficiency order of ignition video that I thought was kinda nice:
This first one shows a furnace with a proving switch problem, at about the minute fifty mark after the flame goes out and re-ignites look above that at the tubing moving. That little bit of movement opened a hairline air leak crack and caused furnace shutdown just for a sec till the switch re engaged;



That one was for proving switch, let's seee, I have the other one somewhere which show sequence of operation:

[coopsterj]

JWWebster, thanks for the info.  It's amazing what a person can find on youtube.  I would never have thought to go there.  While the links you provided were useful, only the 2nd video applies to the unit I have.  There is only one piece of tubing, which apppears to be in good condition, it is only 4-4 1/2" long, comes from the furnace unit itself, and connects to what looks like is a gas flow valve.  (Similar to what you might find on a propane tank).  After watching the videos, I am going to go with bad ignitor.  It appears this is an easy replacement.  What are your thoughts?

[JWWebster]

Unplug the ignitor and check it for continuity. It has a quick plug just like a dryer.

[coopsterj]

This is where it gets tricky for me.  I understand the concept of continuity, but what type of instrument will I need to check for this, and exactly how will it be used?  I apologize in advance for what may seem like ignorance regarding this, but in my years of fixing things, I have not come across the need to know how to check this type of situation.  Again, I appreciate any direction you can give.

[JWWebster]

Each component in a circuit must have continuity. If a light bulb is bad it no longer has continuity, and the circuit is interrupted at that point. To diagnose the problem in most anything you have to locate the interruption in the circuit. Heaters as you may know produce a great deal of heat. Today's modern heater no longer has a a pilot light. It lights itself. That ignitor is just a real mean light bulb. It gets hot enough to light the heater. In the same circuit is a series of safety switches that monitor the heat. If it gets too hot these open and kill the circuit. To test these various components you need an ohms meter. You can get a cheap one anywhere. The power must be OFF to check for continuity. A wire must be removed from each component to prevent a false reading. Any open component is gonna be the problem.
Here is the Fearless leader's handy dandy guide to using test equipment: How to use test equipment

[Icehouse]

This is where it gets tricky for me.  I understand the concept of continuity, but what type of instrument will I need to check for this, and exactly how will it be used?  I apologize in advance for what may seem like ignorance regarding this, but in my years of fixing things, I have not come across the need to know how to check this type of situation.  Again, I appreciate any direction you can give.

[Icehouse]

And this : http://www.allaboutcircuits.com/vol_6/chpt_2/2.html

[coopsterj]

Ok, have my multimeter, a Cen-Tech 92020.  (It's digital)  (Icehouse, I appreciate the diagram showing an analog unit, but I could not find one.)  The Cen-Tech has selections for ohms from 200 to 2000K.  Following the printed manual regarding my multimeter for ohms, I set the selector knob at 200, (which is @ 6 o'clock).  Touching the leads together would not zero it, it would only go to 00.3, and vascilate between 00.3 and 00.6.  The next step up, the 2000 setting would get a zero reading when touching the leads, only without the decimal point.  Regardless, when testing the ignitor itself, and the meter set @ 200 the meter read 93.1, and when set at 2000 it read 094.  When testing the connector coming from the controller, it didn't register anything.  Is the ignitor bad?  I truly appreciate your tutelage.

[jumptrout51]

Please be more specific regarding:
 "the connector coming from the controller".
Thank you

[JWWebster]

Post some photos so we can see what you have.

[Icehouse]

http://www.ehow.com/using-a-digital-multimeter/

[Icehouse]

http://support.fluke.com/find-sales/Download/Asset/1260898_6116_ENG_M_W.PDF

[coopsterj]

The connector I was referring to is the one that connects the ignitor to the controller.  It's where I disconnected the ignitor to check it for resistance, and I thought what the hell maybe I should check going back to the controller.  What would you like photos of?

[JWWebster]

The furnace, the ignitor, the panel. The burner assy. Whatever you got.