Trane XV80 No Heat

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Old 11-05-11, 08:07 PM
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Trane XV80 No Heat

House was a little chilly today, turns out the furnace isn't coming on. Forgive any wrong terms - experienced DIY'er, not somuch with HVAC

Turn thermo up - hear 'clicks', blower comes on, inducer spins for a few seconds then shuts off. I don't see the 'glow' of the igniter at all. Red LED is flashing 9 times then pause. According to manual that means "Check ignitor circuit and line “N” to 24VAC “common” voltage (<= 2 volts) [possible grounding problem]."
I noticed the '9 blinks' a few days ago but the furnace was still functioning then.

Any thoughts or things to check?
 
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Old 11-06-11, 12:10 AM
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You aren't providing enough detail to understand where the furnace is stopping in it's "sequence of operation."

Take the cover off the burner compartment of the furnace.

Turn the thermostat up and describe in detail the sequence of events you see happening.
 
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Old 11-06-11, 12:30 AM
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As soon as I turn the thermostat up to call for heat, I can hear 'clicks' like it's starting the normal routine, I can't tell exactly where they're coming from, just sounds like some kind of relay in the top part of the unit

The blower starts and will continue until I shut off the system.

I observe the inducer motor start, but almost immediately starts to slow down until it stops - this seems to be where the startup sequence (as I understand it) stops

The red LED that you can see through the view port starts blinking fast 9 times then pauses
There's a green LED on the board that looks to be labeled DS3 that comes on at that time as well

I don't hear/smell any gas and I don't see the igniter glow at all

I've cleaned the 'flame sensor' and checked that the hose from the inducer to the pressure switch is clear.

It also may help - there's a 'combustion air' fan in the room that comes on when the furnace is called. It's functioning normally, so I know the call is being made from the thermostat
 
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Old 11-06-11, 05:10 AM
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on the back of the blower door in the schematic is a legend to tell you what the flashes mean. Please post the 9 flash definition here.
 
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Old 11-06-11, 06:54 AM
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You know the thermostat is calling for heat effectively. The next step is that the inducer motor (and power vent motor) should turn on and stay on.

Since the inducer motor is slowing down, you either have a bad inducer motor or inadequate or unreliable voltage to the inducer motor.

Use an AC voltmeter to measure the voltage to the inducer motor. If that voltage stays at 120VAC you have a bad inducer motor. If the voltage is signioficantly below 120VAC the circuit board controlling the inducer motor is bad and needs to be replaced.
 
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Old 11-06-11, 07:42 AM
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hvactechfw

on the back of the blower door in the schematic is a legend to tell you what the flashes mean. Please post the 9 flash definition here.
The back of the door says for 9 blinks it's "Ignition"
The manual says "Check ignitor circuit and line “N” to 24VAC “common” voltage (<= 2 volts) [possible grounding problem]."

Since the inducer motor is slowing down
To be clear - the 'slowing down to a stop' is because it's no longer energized. I probably didn't explain that well. I can dig up my multimeter.
The timing is consistent - I've watched this cycle at least a dozen times now and it's stopping the sequence at the same point and in the same amount of time. The inducer seems to be energized for just a second or two every time.
 
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Old 11-06-11, 10:08 AM
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Well... I have heat now.

I pulled out the trusty multimeter and decided to check the resistance and voltage of the HSI before I checked the inducer motor. From what I've read, it looked good (resistance ~ 14, voltage to during start up ~ 123)
Reconnected the HSI and energized the unit to test the inducer and poof... ignition. I know if checked that for a loose connection before, but didn't actually re-seat it.

Before I claim victory over such a simple solution... could that have fixed it or just coincidence it started this time? I want the house to warm up a bit before I risk cycling it again But I have cycled it at least a dozen times over the last day, probably closer to 20

Thank you both for your time and patience - I am very familiar with how difficult it can be to try to remotely diagnose a problem when the person on the other end can't precisely describe what's happened or use the correct terms/verbiage.
 
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