Spent more time yesterday than i should have on a rooftop trying to figure out why in the hell it kept tripping on high limit. Manual says gas should be at 3.5" on hi fire. Turned it down to 3.0-2.9". Couldnt increase fan speed due to duct noise being the issue or having air blow on you while you're eating. (Restaurant) Manual said nothing for LED codes. Only thing i could figure out was to keep fan on all the time to keep heat exchanger cool. I am probably missing something or the unit has a ghost
Help!
Did you check the temperature rise? Sometimes there's a filter hidden inside that might be dirty.
If the filter, airflow and temperature rise are good then it might just be a bad control board locking out. Was the limit actually open when you were there? There may have been a dirty filter in the past that caused the limit to trip and reset repeatedly. The limit may just be weak and worn out.
Ductwork noise is sometimes a sign it's not big enough to handle the appliances airflow. Maybe it's a bad design / install that causes the unit to overheat.
Forgot to mention the unit was installed 2-3 weeks ago. Filters were brand new. Did not check temp rise. Other thing too is that there were 2 alarms showing up after a while. Said coil 1 and coil 2 were locked due to freezing up.
That's what it came down too. Either the unit has a shitty board, has defective sensor the ducting is sized to small.
Just frustrating when you tell the client "yeah hey.. there is something wrong but I don't know what it is".
Is there an economizer stuck open?
I'd check everything mentioned and also if you think faults are erroneous I'd also check for proper voltages (line and control) and proper grounding.
If it's a re and re, is it bigger unit than what came out?
When does hi limit tripping happened? How long for the blower delay? You say "keep fan on all the time", it can solve the problem?