Trane furnace four flash diag code after 10 mins


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Old 01-07-09, 01:37 PM
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Unhappy Trane furnace four flash diag code after 10 mins

Trans xl14i TDD100R9V5F4 furnace. Three zone. Thermostat controlled via zone controller. Doesn't matter what zone is calling for heat.
Furnace runs for about 10-15 minutes after flame kicks on, then shuts off flame, even though call for heat is still there. Motor continues running. Then after about 20 minutes, repeats. Does this cycle 3-4 times, then blower only. Diag LED flashing 4 times, stops, then repeats each time flame goes away. Panel says "open limit switch"
Any ideas? Air flow seems good at registers, all filters replaced on 30 day interval. Blower hasn't been cleaned in two seasons....

any help is always good help... Thank you all for this forum..
 
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Old 01-07-09, 03:44 PM
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It sounds like the furnace is overheating.

You can test that by checking the temperature at which the limit switch is supposed to open (usually stamped of the switch). Then measure the warm air temperature coming out of the furnace. If that warm air temperature get up to the switch setting and the burner shuts off--- bingo! The furnace is overheating. I'd also measure the voltage on the limit switch and verify that the switch opens, shutting off the voltage and the burner.

If that's the case, you need to check why that is happening. Very likely something is impeding the air flow through the furnace, allowing it to over heat.

I'd check the cold air return register(s) to make sure they aren't covered up and the controllable dampers to be sure they are actually opening. Check the blower wheel to see if it is clean or possibly loaded with dust or debris of some kind.

You may want to use a monometer to measure the static pressure across the furnace and long the ductwork to see if it exceeds the maximum specified on the rating plate of the furnace.



That it takes twenty minutes to get to this condition suggests it's not an extreme condition.
 
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Old 01-07-09, 04:00 PM
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Thanks

I'll take a look at all that.... thanks for the info...

ED
 
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Old 01-07-09, 04:40 PM
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where is it

where is the limit switch you recommended I check and what voltage should I be seeing? I, like many others I'm sure, wish I had a manual for this unit. exploded view would be nice. The door panel has the scat on it, so I know where everything is "electrically" but physically I'm hunting with a blind dog.
 
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Old 01-07-09, 04:44 PM
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If you can post some picture using the insert image icon on the posting page, perhaps we can point you in the right direction.

Pictures of the whole furnace and the burner compartment would be valuable.
 
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Old 01-07-09, 05:58 PM
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I do not have the means to take digital photos at this time....
 
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Old 01-08-09, 03:33 PM
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pictures

I posted some pics on Flickr. search for edvan41 under people. there are 5 pics there.
 
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Old 01-08-09, 04:09 PM
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My guess is that per your second photo, it is the reddish fiber looking plate, that looks to be about 2 x 3 1/2 inches on the furnace to the right of the burners, and to the left of the upper Hot Chaud.

It would be 120 volts AC or 24 volts AC. Set your meter to a range that is at least 120, and 24 will also show up, if that is what it is.
 
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Old 01-09-09, 03:19 AM
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will check it out, thanks for the info
 
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Old 01-09-09, 03:32 PM
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it's me again...
here's what I saw now that I am looking at it more closely. Since I don't have a helper and my furnace is in the attic, I wasn't sure how long the blower stayed on after flame started.
So, here's what I did.
I turned the heat up 5 degrees from room temp, ran up to attic and observed. vent motor started spinning, ignitor glowed, flame kicked on, blower was blowing hot air out around where the ac line goes into the coil (it's not 100% sealed). everything was working fine. then, no more air flow! flame still rolling along, draft motor spinning away, just no blower blowing. in about 15 seconds, the flame went out. so I think everything in the limit circuit is working as it should, thank goodness, cuz it got hot really quick without airflow.

what would cause the motor to just shut off like that? since it's two stage, what can I check on it? the furnace is only 5 years old, which means we are in our 4th heating season. blower bad already?
tell me if I am crazy or not, please.
 
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Old 01-09-09, 05:02 PM
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You likely have a board where you can find where the wires from the blower motor are plugged in. Look for words HEAT and COOL (or A/C) and PARK. There will be more wires connected to the board also. For example, you probably have HEAT1 and HEAT2. I'm really not sure, exactly, but the bottom line will be these are your blower (speed)wires and any wire plugged into HEAT will be the hot feed to the blower motor. Use voltmeter and test to see if you have 120 volts at both HEAT connections, by testing between one of them and to the white neutral wire. Do both HEAT(s) to neutral. And you can also test from HEAT connection to metal of the furnace. Make sure connections are tight. Let us know what volts you have at those conections when blower runs and what happens when blower quits.

The board may be located in a metal box perhaps mounted in front of blower motor.

This post is just some general info that may help you, not based on your model furnace, per say, but general furnace operations.

If you show power continues at HEAT connections, even though blower quits, and the connections are good, suspect motor going out on overload.

But if the HEAT connections to blower go out, then I'd say you have some kind of relay (located on or off the board) or timer control, that is bad. I can't help you much more than that, without being there and seeing where wires go, myself. And/or to look at some wiring diagram.

And -I am not sure if your stat is wired in some way to 2-stage fan, as opposed to simply all controlled at the board, with a 2 stage set-up like you have. Someone like moderator Jay11J, could shed some light on this, as he often answers people about thermostat issues and wiring and 2-stage set-ups. Or, others here that may care to jump in.

After re-reading your post - the fact the flame then goes out 15 seconds after the blower, and yet there is this call for heat still going on, I find interesting. There is something more going on here than just the blower motor (circuit). Maybe. Seems pretty odd the furnace would high limit and shut off the flame in only 15 more seconds. Unless it was already on the cusp. But I'm sure the high limit SOLEY is not the issue, because the flame should shut off right away when limit trips (I think - unless you have a relay that delays it), and not the blower first. Actually, when most newer furnaces limit they actually cause the blower to keep running, to cool the heat exchanger back down to acceptable levels. And that too makes it seem unlikely you have a limiting issue.

Test your thermostat circuit to make sure that current that is flowing out of low volt terminal strip in furnace is not shutting off during call for heat. That is what I'd check for starters. I sound like a broken record with that reply in many of my posts, but it is important to rule out if stat functions are shutting off even if call for heat still exists. The tests are fast and cost nothing. Go right on down the line and see if you have R to common, W to common, G to common etc., etc., and still have it when the blower quits, and also when the flame quits (with the call for heat stil going on)
 
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Old 01-09-09, 05:16 PM
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Thank you for the information. I do know the heater has been working for quite some time now, so don't know if thermostate wiring is an issue. could be and just caused a slow failure over time of something. maybe others can help out. i hope so, with the economy, i don't have the money right now for service tech and it's frickin cold.
 
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Old 01-09-09, 05:43 PM
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Look at things I suggested. I can't help any further. Multiple stage systems are more complex. Some others are online now and still others (like mods) may be out for Friday fish fry?
 
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Old 01-13-09, 12:06 PM
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Thumbs up

Turned out to be the board.... thanks to all who gave suggestions/information.
 
 

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