Trane XE90 High Limit after 5 min of use


  #1  
Old 11-24-13, 11:01 PM
I
Member
Thread Starter
Join Date: Feb 2009
Location: USA
Posts: 303
Upvotes: 0
Received 1 Upvote on 1 Post
Trane XE90 High Limit after 5 min of use

Had a few hiccups with this system but was working fine last winter. Replaced a failed ignitor and had to clean the flame sensor a few times with some steel wool but now after the first time the heat was called for this season, the unit is shutting down after 5-10 min of use.

The blower fan was replaced last year as it completely failed and that was during the cold months, worked fine after that and the speeds are correct. I cleaned the flame sensor and the contacts, cleaned the contacts of the high limit switch, but I didn't check for continuity yet.

Filters are clean and there is good airflow through the registers. Does this sound like a high limit switch or possibly a board? I will check again tomorrow and see if it is still acting up but after I did the cleaning it did satisfy the stat once so far and stayed running. Could be a fluke but who knows.
 
  #2  
Old 11-25-13, 09:12 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 65,108
Received 3,986 Upvotes on 3,578 Posts
cleaned the contacts of the high limit switch
High limit switches are usually sealed. I'm not sure what you cleaned.
The flame sensor rod has no bearing on this problem.

If the burner is shutting off due to high heat exchanger/plenum heat issue then it's usually caused by a filter, blocked return vents, too many supply registers closed or dirty A/C evaporator coil.
 
  #3  
Old 11-26-13, 08:14 PM
I
Member
Thread Starter
Join Date: Feb 2009
Location: USA
Posts: 303
Upvotes: 0
Received 1 Upvote on 1 Post
The high limit switch, I suppose it's the 3" long, 195 deg piece just under the plenum? I just made sure the two spade connectors were clean.

Now the A/C coil is where I think you may have guessed it...this isn't my system but I'm fairly confident it hasn't been touched in 4-5 years. I will check it out.
 
  #4  
Old 12-01-13, 07:06 PM
I
Member
Thread Starter
Join Date: Feb 2009
Location: USA
Posts: 303
Upvotes: 0
Received 1 Upvote on 1 Post
Update....unit still kicks off after about 4-5 min. I puled the A/C coil out and cleaned it, used a brush on the inside and was in pretty decent shape....not too dirty but a slight hint of dust on the coils.

Here's what I have and the ohms measurements with the leads disconnected.
 
Attached Images  
  #5  
Old 12-01-13, 07:44 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 65,108
Received 3,986 Upvotes on 3,578 Posts
What I would do is set the meter to read 24vac and when the unit fails..... measure across the switches.... one at a time. If the switch is open/faulted you will read 24vac.
 
  #6  
Old 12-01-13, 08:35 PM
user 10's Avatar
Member
Join Date: Mar 2004
Location: NA
Posts: 1,829
Received 57 Upvotes on 50 Posts
If the high limit is what's tripping...

1. Measure the temperature difference between the supply and return. Make sure that it's within the range spec'ed out on the nameplate. (temp rise is the properly term)

2. Clock the meter (Clocking a Gas Meter - Home Energy Pros) to make sure that the furnace isn't overfired. If it is, call a tech to check the gas pressure.

If not, check the blower wheel for dust and dirt -> if the wheel is dirty, the secondary heat exchanger right above it probably is too. (have blower + secondary cleaned)

Rule out the obvious stuff like closed vents and maybe if you're using one of those 1" pleated filters, try fiberglass.

Raising the fan speed may be an option after everything else is ruled out.

---------------
Normally coil cleaning should never be necessary.
 
  #7  
Old 12-24-13, 07:39 AM
B
Member
Join Date: Dec 2013
Location: USA
Posts: 3
Upvotes: 0
Received 0 Upvotes on 0 Posts
A relief

To those of you who have an XE90, I found the problem of limiting out due to overheating. After many failed attempts by "furnace experts", I totally disassembled my furnace down to the heat exchangers, then reassembled only to have the same problem. I took my filter out so I could see the top of the fan and felt the blades to see if they were dirty. There are noise dampeners surrounding the cabinet that houses the fan. I started the furnace while looking in the cabinet and when the fan started it sucked all three of these dampeners right to the fan thus suffocating any air flow and causing my furnace to limit out. After tearing those pieces out the furnace sounded like a jet engine. Everything is running perfectly now. I have been fighting this for two years and will probably never call another tech as all they wanted to do is sell me a new furnace. Very poor design by Trane. Hope this helps a ton of other people with the same problem.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: