Lennox G12 Blower Runs Constantly

______________________________________________________________________ Hi, Guys. I’ve checked the existing posts on this subject. They are different in that they started from a “known good” condition. I am not. I acquired this house as a rental. The renters complained that the blower ran all the time, so I hired a service guy to come out and fix it. He fiddled around, told me the blower motor was bad, charged me $300 or $400 to replace it (I forget), then left.The renters didn’t complain anymore, so I didn’t realize it was still broken until I moved into the house myself. The furnace has 4 wires going to a Honeywell T8084 thermostat. 2 of the wires are connected. I had presumed this was normal, and fan control is normally done by the furnace (limit switch). However, I suspect somebody has done some “amateur wiring” on this. Where the power comes out of the wall, it feeds into two, single manual switches (marked “fan” and “heat”) before feeding into the furnace. I do not understand what I am looking at. Here’s why: It would make sense if these only functioned as some sort of cut-off. However, if you flip either one of them on, the fan runs continuously. The flame cuts on and off correctly, but the fan runs at all times. Also, I have never seen switches wired like these. They look like regular 120V single pole switches (like a light switch). But a normal switch would have a wire at the top, and a wire at the bottom, making connection when you flip it. These are wired at the top only, and the switches are jumpered together at the top. If you flip either one, the fan goes on. Would it make sense to eliminate these switches, and run power straight into the furnace? I am trying to eliminate as many variables as possible so I can check for correct basic function. If I do wire straight in, and the blower runs all the time, can I assume there is a problem with the limit switch? My Domestic Goddess wanted the heat to totally cut off at night, so, while tinkering with this, I have replaced the thermostat with a Lux 500 programmable that has wire connections for fan control. Would it make any sense to connect this, or am I just confusing the issue? I am pretty ignorant on HVAC, so if anybody could confirm that normal operation for the G12 is two wires to thermostat, fan control accomplished at furnace by limit switch, that alone would assist in troubleshooting. Any suggestions from you folks who are proficient in this arena would be greatly appreciated. Have a good day, Steve Replies: Xenos Webmaster “Re(1):Lennox G12 Blower Runs Constantly” , posted Tue 10 May 21:50 ______________________________________________________________________ I wouldnt worry too much about the switches since both appear to operate. instead I would concentrate in the fan/limit switch Xenos. The best way to escape a problem is to solve it. chronicnetpro “Re(2):Lennox G12 Blower Runs Constantly” , posted Wed 18 May 21:17 ______________________________________________________________________ Thanks for that suggestion. I replaced the fan/limit control, Honeywell L4064A (8 inch) with Honeywell L4064B (8 inch). I guess my number was obsolete and this is the replacement. Anyway, after replacement, symptom doesn’t change. I noted this warning on the new switch:”Failure to remove brass jumper, if limit switch is in low voltage circuit, can cause electrical shock hazard or damage low voltage controls.” I wasn’t sure about this, so I checked the old switch. Slightly different style, so I couldn’t tell if it had once had a jumper. Checked it with ohmmeter, no continuity, so I assume whatever type of jumper it once had has been removed. For that reason, I removed the jumper on the new switch. Could this be the problem? I can’t imagine having the same issue with a brand new switch. Xenos Webmaster “Re(3):Lennox G12 Blower Runs Constantly” , posted Wed 18 May 22:20 ______________________________________________________________________ Acording to the wiring diagram the limit is low voltage and the fan side is high. The fan side if the fan/limit switch controls the low speed ( red wire) fan and the fan relay controls the High( black wire) Xenos. The best way to escape a problem is to solve it. chronicnetpro “Re(4):Lennox G12 Blower Runs Constantly” , posted Thu 19 May 14:06 ______________________________________________________________________ Thank you. My understanding from that message is that the limit control IS in the low-voltage portion of the circuit, so the jumper SHOULD be removed. I believe it is correct. The furnace functions as it did before fan limit replacement (blower runs constantly). Would I be correct in thinking that the fan relay might be faulty? Is it included in the fan/limit housing or located elsewhere on the furnace? If I can locate this, I will try replacing it as well to see if symptom stops. Xenos Webmaster “Re(5):Lennox G12 Blower Runs Constantly” , posted Thu 19 May 21:35 ______________________________________________________________________ It’s looking that way to me. Xenos. The best way to escape a problem is to solve it.

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