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Old 01-25-2011, 05:12 PM   #1
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Trane limit switch


A buddy of mine went to work on a Trane furnace 2 days ago.

Furnace is about 6 years old.

I asked what it was doing or not doing, the only info. that he said that was useful was it blinked a code for an open limit.

So I looked at it yesterday this is what I found.

He bypassed the upper limit and installed a new ignitor.

I ohmed out the limit it was good

Gas valve would open but no flame, so I lit it with a torch.

Every thing worked fine.

So we robbed the ignitor from another furnace in the attic and the unit was up and running.

I then put the removed ignitor "the one he thought was bad" on the doner furnace and both were up and running.

We were getting ready to go and a roll out limit tripped.

We jumped it out and he went to replace it today, only to find out the other roll out tripped.

I was busy on the other side of town so another tech went to help him out.

They increased the fan speed and put new limit switches on it.

I can't see how both limits could have been bad, there was no sign of the flames rolling out.

It worked all night but stopped this morning.

Could the fan be cutting out to make the limits trip?

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Old 01-25-2011, 05:50 PM   #2
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Trane limit switch


Could be fan,gas over fired or too small of duct tripping the limits. None of that would make a roll out switch trip though. That would be a cracked heat exchanger, blocked flue or inducer dragging. A magnahelic on the inducer will test the draft and also use it to test the duct . Every tech should have one or a digital equivalant on the van.

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Old 01-18-2012, 12:49 PM   #3
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Trane limit switch


wow.............
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Old 01-18-2012, 01:00 PM   #4
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Trane limit switch


Tripped roll-out limit means plugged flue or ht ex or a cracked ht ex cang.

Fan has nothing to do with it. Both switches did what they should do in case of an unsafe issue arises , they stopped the gas flow.
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Old 01-18-2012, 01:35 PM   #5
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Trane limit switch


Quote:
Originally Posted by harleyrider View Post
wow.............
Quote:
Originally Posted by hvac5646 View Post
Tripped roll-out limit means plugged flue or ht ex or a cracked ht ex cang.

Fan has nothing to do with it. Both switches did what they should do in case of an unsafe issue arises , they stopped the gas flow.

I agree....Lucky nobody died..... and hopefully significant additional damage has not been done from bypassed safety devices... Flame rollouts don't need "flames" to work.

Last edited by Technow; 01-18-2012 at 01:37 PM.
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Old 01-18-2012, 09:27 PM   #6
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Trane limit switch


I hope your buddy is not a service tech. If he is he is going to kill someone. We all started off like him trying to do this field but something like that is not good. Most Johnstone supply offer monthly classes.
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Old 01-18-2012, 11:16 PM   #7
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Trane limit switch


Wow old thread.
FYI he is 11 years older then me and pretty much a parts changer.
He put in a universal ignitor that didn't work so the unit was down until the next day when I went to look at it with him.
It was a two system in the attic so the other furnace was 3' away, in less the 5 minutes I robbed the ignitor from the working furnace on put it in the down furnace.
I asked what it was doing before he messed with it and all I got was babble, so I got up the tools and was heading out when the roll out kicked the unit off.
We were in his truck and he had no roll out switches so when we got back to my truck I gave him a switch he said he might go back that day or the next.
This gets even better the next day he takes a so called lead tech. out there to help him, this so called lead tech. sold him a 3 phase unit the other day and tried to tell him it would work on single phase power by hooking up two L1 and one L2 to it.
Well guys that's how it goes in a right to work state where pride and quality never gets in the way of getting the job done.
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Old 01-18-2012, 11:46 PM   #8
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Trane limit switch


who or why do these old threads keep getting resurescted? can we lock them after a certain time frame?

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