MIL calls says her furnace is out. I guess it must be catching. Anyway, I go out there and the controller trouble light is blinking 4 times: open high limit switch.
This furnace has two limit switches, one in the plenum where the burner tubes are, and one up on the blower housing. A tripped limit switch is not to be taken lightly, but I've experienced these switches opening for no good reason before. The blower is on the intake side, so that should never be warmer than room temperature. My suspicion is that it's the switch by the burner that has tripped. That switch is also a lot easier to reach. I tried jumping it and it made no difference. Groan, the other one is impossible to reach without doing some disassembly. 30 minutes later I have reached it. I notice that one wire is dangling free. A-ha, simple fix. I reconnect the wire and buckle everything back up. Turn on the furnace and --- 4 blinks, open high limit. DAMN. I must have knocked that wire off earlier when I was feeling around for the switch before I realized I would need to take things apart to get at it. Even with the obstructing parts removed, I still can't see the switch directly. It's on the rear side of the blower fan housing. I have to use a small mirror. It looks like there is a small tab in the center that looks like it might be a reset. I press it, and it clicks. Hopefully, I reassemble the furnace for a second time. Turn it on, and it lights up! So, I'm happy, but still there's that nagging thought "why did it trip out in the first place?" I walk around the house and feel the registers. Not much airflow. I changed the filters while I had everything apart, so it can't be dirty filters. What's going on? About 5 minutes have passed now and the furnace shuts off. 4 blinks: open high limit. WTF? I start removing pieces for the THIRD time, and my hand touches the back side of the blower motor. It's scalding HOT. A-ha, I think again, NOW I now what's going on, the motor has a bad bearing, it's not turning fast enough, and the furnace is overheating. So out come all the parts again, plus a few more so I can get the blower out. It's actually pretty easy to remove, 5 screws and the whole assembly slides out. So I have it on the floor and I spin the fan. It spins freely. I was expecting it to be hard to turn. So now I'm wondering if I'm chasing another dead-end. Can an electric motor have a bad bearing or otherwise overheat and not be obviously hard to turn? I'm going to take it in to a shop tomorrow to see if it can be tested; unfortunately the one real electric motor specialty shop here has gone out of business, but there is another electrical supply shop that says they service motors. Allan _______________________________________ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
