Where is the high limit switch on a Trane XE90?

Does a high limit switch on a nat gas furnace have a 24v continuous current leading to it?

• Currently my Furnace's 4 blinking lights has lead me to test the High limit switch which reads closed (0 ohms). However would I read voltage going to the switch if I tested either lead to ground? If so I think I may have a problem with my control board possibly because I don't show anything going to it. The other jumper switches test good also. Thanks in advance, Steve

• Answer:

  It's a tricky question, and depends on the particulars of your furnace. In any case, I wouldn't expect to get anything to the high limit unless it was actively trying to ignite / heat. That being the case, I'd expect that yes, you should get 24v to / through it If the 4 "blinks" are leading you to the high limit switch, I'd first ask if you're sure you're testing the correct limit switch. There should be at least one high limit, a roll-out switch and possibly a vent spill switch. Roll-outs are sometimes manually reset, and vent spill switches are nearly always manually reset. (Tiny red pop-out button) The quick and easy way to test would be to simply pull the wires from the limit and put a jumper across them, guaranteeing that it remains a closed circuit, then power up the furnace, initiate a call for heat and see what happens. Give it a try and re-post. Hope this helps.