Trane XE 70 will not light.

Old 12-13-11, 08:16 PM
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Trane XE 70 will not light.

My Trane XE70 Model No. TUS100B936A will not light. When I turn it on I can hear a click, a pause, then I hear what might be the gas valve opening and what I think is gas for a second or two then all shuts off. I don't see the glow of the electronic ignitor at the time it is supposed to come on. What can I do to troubleshoot?

I've included pictures to help. I've also posted photos and a video below. Be sure to turn up the volume when you view the video so you can hear the noises I am talking about.
Old 12-13-11, 09:25 PM
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Here is where the manual ofn the ignition control can be found:

In a typical system, a call for heat is initiated by closing the
thermostat contacts. This will energize the 50E47 control.
If the system is equipped with prepurge, the prepurge fan
or interfacing relay is also energized through the thermostat
contacts. In the prepurge mode, the 50E47 control will
delay 30 seconds before applying power to the 767A
silicon carbide ignitor. If prepurge is not an option, the
ignitor is powered within one second.
The ignitor is then allowed to warm up for 17 or 45 seconds
depending on the 50E47 control dash number being used
(see Timing Specifications table). Various ignitors on
the market must use the 45-second option to allow them
to fully attain ignition temperatures at low voltage conditions.
The W-R 15-second ignitor is especially designed
to heat up quickly at a low voltage condition without
overheating at a high voltage condition. Thus, the W-R 15-
second ignitor may also be used with a 45-second warmup
time without detrimental effects.
At the end of the ignitor warm-up time, both valves in the
36E manifold gas valve are opened. The ignitor will
remain on for an additional one second (ignition activation
period). A four-second ignition activation period is also
available. Flame must be detected within four seconds (a
seven-second trial for ignition period is available as a
separate type). If flame is not detected, both valves are
de-energized, the ignitor is turned off, and the 50E47
control goes into lockout.

There should be a seventeen second warm up period for the hot surface ignitor before the gas valve is switched on.

If your description is accurate, you aren't getting that warm up period. If so, you need to replace the module.

Double check to be sure that the gas valve is being energized and not the hot surface ignitor. Check the voltages on both to see what is actually happening.

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