Over Temp Fault, checked everything, ideas? - http://www.hvacmechanic.com/ Forums
Original message
| Pldbryan
 |  "Over Temp Fault, checked everything, ideas?"
, posted Fri 6 Jun 18:01  
This has been a very helpful forum and I have been using it for the last few days and has provided some good guidelines.
That said I have a Trane XB80 that keeps faulting on code 4 High Temp Limit. I have pulled filter and replaced, opened up the AC Coil area adn cleaned it although it seemed very clean. Dampener is in the correct position and vents are clear. Everytime I reset it, it will run for a bit and then fault again. The switch can not be stuck becuase it will reset.
I am thinking about replacing the entire control board but would like to narrow it down so that I know that will fix the problem.
If there are any ideas out there are all please let me hear them!
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Replies:
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| theduke03
| "Re(1):Over Temp Fault, checked everything, id" , posted Fri 6 Jun 18:43:
Was that the top side or the bottom side of coil that you cleaned? The bottom side is what has to be cleaned. I see no reason to replace the control board unless you're trying to give away money. If so let me know. I could use some.
Is the blower running?
"My dad was the most feared furnace fighter in Northern Indiana."
[this message was edited by theduke03 on Fri 6 Jun 18:44] |
| | Pldbryan
| "Re(2):Over Temp Fault, checked everything, id" , posted Fri 6 Jun 18:49
That would be the bottom side and the top side. Yes the blower is running. I have also tried to run it without the filter in just to double check and it still faults.
Potentially a bad temp sensor? Not sure on how to check besides open and closed.
Trying to save some $, that is why I am posting here as opposed to being on the phone with the heating company to come out here.
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| | theduke03
| "Re(3):Over Temp Fault, checked everything, id" , posted Fri 6 Jun 19:21
So you're saying that you removed the A plate on front of coil and cleaned the underside? There are really only 2 reasons a limit switch would trip. 1= lack of airflow. You say coil is clean, vents are open, dampers are open, blower is running, filter is clean. Do you have a zoned system (more than one stat)? If so you could have a zone damper stuck closed.
Otherwise take a temp reading at vents with furnace running and post results. I would like to know the return temp and supply temp.
"My dad was the most feared furnace fighter in Northern Indiana."
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| | beginner
| "Re(3):Over Temp Fault, checked everything, id" , posted Fri 6 Jun 18:57:
Have you clean the condensing coil? It is the outside unit.
[this message was edited by beginner on Fri 6 Jun 18:59] |
| | theduke03
| "Re(4):Over Temp Fault, checked everything, id" , posted Fri 6 Jun 19:13
quote:
Have you clean the condensing coil? It is the outside unit.
...
How is that going to cause the furnace to shut down on limit?
"My dad was the most feared furnace fighter in Northern Indiana."
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| | beginner
| "Re(5):Over Temp Fault, checked everything, id" , posted Fri 6 Jun 20:37
Oh sorry, I didn't know you were still in the heating mode.
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| | Pldbryan
| "Re(4):Over Temp Fault, checked everything, id" , posted Fri 6 Jun 19:01
No, would this be on the AC unit outside?
I have cleaned the filter and also the AC Coil inside the furnace. If there is another one, point me to it and I will clean it!
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| | Pldbryan
| "Re(5):Over Temp Fault, checked everything, id" , posted Fri 6 Jun 19:42
Yes I pulled a kind of two piece cover off and then there was an A Shaped radiator/coil inside. It had a metal shield that covered the A Shape so I pulled that off.
There was no debris or build up on the surface so I took some low pressure air and blew though the coils. Nothing really came up and it looked clean so I figured it has to be letting air go through.
All of this seemed pretty wierd to me too. I will have to see if I can take a temp reading on the air. Should I just put a thermometer on a vent?
A bad sensor would make sense but I am not sure if I can check the resistance on it or what to make sure it is operating to sped.
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| | theduke03
| "Re(6):Over Temp Fault, checked everything, id" , posted Fri 6 Jun 20:02
OK so the coil is clean. I just had to be sure you weren't being a homeowner about it. The sensor you speak of is a limit switch. It simply is open or closed. The reason for checking temps is I want to know the temp rise thru furnace. There is a range on the nameplate inside furnace something like: Temp. rise 45-75 degrees. If your temp rise is higher than nameplate specifies then your problem is with airflow. If not it could just be a bad limit switch but this should be verified.
You should jumper the limit switch to do this test so it doesn't shut off prematurely. Or just remove the 2 screws and pull it out of the furnace. Post results.
"My dad was the most feared furnace fighter in Northern Indiana."
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| | Pldbryan
| "Re(6):Over Temp Fault, checked everything, id" , posted Fri 6 Jun 19:52
Well I reset it and put a temp gauge on a vent. It trips after about 1 minute of running and my temp gauge does register the change fas enough.
It is a single zone system and I have the dampner set correctly.
??????
Any other ideas are welcome.
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| | Pldbryan
| "Re(7):Over Temp Fault, checked everything, id" , posted Fri 6 Jun 20:07
I will jumper it, good idea.
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| | Pldbryan
| "Re(8):Over Temp Fault, checked everything, id" , posted Fri 6 Jun 20:43
OK, Vent temp got up to about 91*, intake temp was about 71*.
I pulled the jumper out and started it back up and it immediately tripped on hight temp limit.
I am going to let it cool down and restart. I would guess that it will run for a bit and then trip.
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| | theduke03
| "Re(9):Over Temp Fault, checked everything, id" , posted Sat 7 Jun 08:36:
There is no way you have a 20 degree rise thru the furnace. Do the test over. You can stop reading supply temp if it passes the temp rise listed on nameplate. Having said that it shuts down in 1 minute suggests it's just a bad switch. When you replace it we will know for sure.
So how was the airflow at your vents?
"My dad was the most feared furnace fighter in Northern Indiana."
[this message was edited by theduke03 on Sat 7 Jun 08:37] |
| | Pldbryan
| "Re(10):Over Temp Fault, checked everything, i" , posted Sat 7 Jun 13:39
AIrflow was really good at most vents and did seem a little weak at two of the vents. I have probably 15-18 vents around trhe house. I may go get a new switch and try it out.
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| | Pldbryan
| "Re(2):Re(10):Over Temp Fault, checked everyth" , posted Fri 20 Jun 17:42
Just as an update it did end up being the control board that needed to be replaced. Did it and all is good.
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