Hello,

I have a Trane XE80, model number TDD080C936E0. A few weeks ago, it started blowing only cold air with error code 4 - high temperature limit open. If I shut it down, and start it up again in about an hour or so, sometimes it comes back on, sometimes it doesn't (produce cold air only). For those times when it comes on, sometimes it stays on for half an hour, sometimes a couple hours. This sympton makes me think something is causing the furnace to sense a high temp and the high temp switch is probably working as it supposes to. Does it sound right? I have all the ducts cleaned about a year and a half ago, the air filter is new. I'm thinking of having the ducts cleanned again and that may solve the problem. Do you have any suggestions? Should I replace the high temp limit switch, or the circuit board?

Thanks for your time!

Don't rush to start replacing parts until you assure there aren't underlying issues with the system. You are correct in suspecting overheating, but replacing the limit won't solve a problem like this. Duct cleaning has the potential to stir up all sorts of dirt, and it may have collected on a secondary heat exchanger surface or an air conditioning coil, creating an airflow restriction. I would recommend a professional evaluation for the long-term benefit of your system and your wallet.

I was just out talking to my neighbor and apparently he said his furnace (also an Trane XE80) had a the similar problem about a month ago. A technician friend of his replaced the circuit board for him for $350 and he said it's been fine since then. This technician also just recommended me to do the same thing. Since his furnace quit completely, and mine is kind of off and on, I hate to spend $350 on something which may not be the underlying issue like you said. From my description here, do you think the board could have been fried? He was very sure that it is the board but I am not 100% convinced.

Trial-and-error parts replacement is a potentially costly alternative to effective troubleshooting. What does "similar" problem mean-no heat? Just because your neighbor's headache required neurosurgery, doesn't mean yours will also. Even if you both have the same hat size. Use some of the thread tools to see if you can find any cases of the "same" problem as yours, and what the corrective action was.