Short time lurker , first time poster . I had a Trane XV 95 furnace , XR 14 a/c , Trane Clean Effect air cleaner installed today . The furnace didn't pass the "sea trials" , the diagnostic light tripped , blinking 4 times saying the upper limit switch was open . They opened the blower cover , it tripped again . They drilled holes in the vents and got temps of 135 F . I didn't get scared till they started adjusting the high and low screws on the valve , which didn't stop it from shooting codes . They are sending a service tech out tomorrow w/ a new upper limit switch . I'm hoping that solves the problem . What a disapointment for all of us , nothing worse than getting to the end and not having it work . Forgot to mention it takes about ten minutes till shut down . I hope it is as simple as the switch . I assume it isn't a common problem. Sorry if this was a long read.