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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a trane xe-78 which is not working. The flame sensor

Customer Question

i have a trane xe-78 which is not working. The flame sensor is ok. The ignitor glowed the first time I tried it, but not since. and the blinking code is 4 blinks which is a temperature control circuit. It is snowing and I would like some heat!
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: I have checked the thermostat which is off now as I was working on it. The filters are clean.
JA: Do you plan on doing the work yourself?
Customer: Only option
JA: Anything else we should know to help you best?
Customer: Not that I can think of. I think it is relatively inexpensive to replace the ignitor and I can see how to do that. What else should I be thinking of? The unit is 23 years old, but has been fantastic.
Submitted: 7 months ago.
Category: HVAC
Expert:  Phil replied 7 months ago.

Hello, send me a photo of the units wiring diagram glued to the inside of the furnace access panel, photo must be well lit and *exceedingly well focused. and a photo of the printed circuit board where the wires from the thermostat attach.

I will mark those up with trouble shooting instructions.

Use the attach files link next to your send button to attach the files

Expert:  Phil replied 7 months ago.

The odds of you fixing this without parts in the snow however are minimal... you should have plenty of back up heat available, such as a few portable electric space heaters or a kerosene heater (use only with a window cracked open 2")

Customer: replied 7 months ago.
Ok. Sorry out of touch.
Expert:  Phil replied 7 months ago.

Thanks, ***** ***** the diagram

do these tests click here

Expert:  Phil replied 7 months ago.

If you have 24vac between R and C with the blower door switch held in, put the blower door back on and turn the thermostat OFF at the thermostat, wait 5 minutes then have someone else turn the thermostat back ON and set the heat to 90F as you stand next to the furnace listening intently for the following in this order"

Small induce fan comes on

in 2 seconds you hear a faint click, and inducer fan continues to run

in 30 to 50 seconds you hear two faint clicks as the igniter relay closes and the gas valve relay closes

next you hear the burners ignite.

If the burner ignites tell me how long it stays lit until it goes off.

You may want to repeat this test a few times to get familiar with the sounds.....I can tell from what you hear far along the furnace is getting in its firing sequence and from that what the problems are.

Customer: replied 7 months ago.
OK, Phil... I'd have you call but I don't hear well. So what is happening... I do have the 24voltage between R & C. I don't have anyone else to help with the thermostat, but I've run back and forth. The igniter relay does not work and the igniter does not glow anymore. I have replaced the igniter today, as I broke the old one when checking it. The flame sensor is clean. Now what?
Expert:  Phil replied 7 months ago.

Hello again, the printed circuit board is most likely bad, but there can be other problems.

Connect your volt meter to the female side of the igniter plug, and if you get voltage there. Next repeat the test but at the wires that connect to the gas valve, tell me what you can discover.

If you can take a photo of the wiring diagram glued to the inside of the blower service panel I can mark it up with trouble shooting instructs,. photo must be taken close up and exceedingly well focused... us the attach files link to the left of your send button to get that to me.

We can go from there

Customer: replied 7 months ago.
Here they are. Thank you SO much.
Expert:  Phil replied 7 months ago.

Thanks, ***** ***** photo of the ignition module, I need a picture of 8 x 11 inch sheet of paper that is *glued to the inside of the blower access cover. and it needs to be better focused and more close up than the photo's you sent of the ignition module.

We can go from there

Customer: replied 7 months ago.
OK. I'll try.
If the blower access cover is up above the other two panels (IMG 1005) then I can't get get into it. It is taped, screwed, etc and fixed in behind those pipes. If on the other hand the blower access cover is one of the other two covers. Then all the other info is in the other pictures. I know this must be very frustrating for you also. I have a repairman scheduled for tomorrow as my back up plan.
Expert:  Phil replied 7 months ago.

Thanks, ***** ***** work, I came up with tooth thats killing me so I am in no shape to answer now