Ask Experts Questions for FREE Help !
Ask
    jjet555's Avatar
    jjet555 Posts: 3, Reputation: 1
    New Member
    		  
    #1

    Jan 13, 2007, 12:17 PM
    Fan on lennox furnace won't run
    Hello

    I have a 20 year old Lennox Conservator 3... gas furnace/AC combination unit.

    The problem started as: When I set the thermostat to "heat" and fan on "auto", the burner would light and stay on for a few minutes then shut down (as it is supposed to do) because the fan was not coming on. If I turned the fan to "on" and set the thermostat to heat, the fan came on and the heat came on... that worked OK in a pinch except the fan didn't shut off when the heat shut off (as it is supposed to do because the fan was in "on", not auto). I have a fan limit switch ordered for Monday, because I thought that was the problem. Today, the problem has changed. Now the fan won't come on at all, in either position. When I put the fan to "on", I hear the relay come on (I assume) and the squirrel cage looks like it is trying to run (barely moving) and you can hear that something is straining to run, but that is all it does. The squirrel cage turns free when I rotate it.

    I blew out all the dust that I could get to in the motor, but I don't know what else to check for. The fan limit switch I have is the exact one you have pictured above. Could this be the problem?

    I appreciate any help or suggestions.
    y4hdesigns's Avatar
    y4hdesigns Posts: 5, Reputation: 2
    New Member
    		  
    #2

    Jan 13, 2007, 01:59 PM
    Dumb thought, but have you verified the thermostat is good? I wonder if it's not sending the right signal to the furnace.

    Also, I had a situation where my furnaced stopped working because there was a small hole in an internal line that caused the safety mechanism to kick in.

    Just some thoughts, sorry not of more help.
    labman's Avatar
    labman Posts: 10,580, Reputation: 551
    Uber Member
    		  
    #3

    Jan 13, 2007, 02:14 PM
    I doubt the thermostat is the problem. You can easily verify that by jumpering the R and W terminals at the furnace. In heating mode, all the thermostat does is to connect them. If the blower still won't run, the problem is in the furnace. Quite often the relay done it, but your other info suggests the blower motor is dying. You have separate windings and relays for low and high speeds in auto and ON. Sounds like first the low speed winding died, and now the high is going too. You can check it again with a jumper from the incoming 120 volt black wire from the house to each hot lead of the blower motor. If the blower motor takes off and runs, turn you attention to the relays. Give the 120 the respect it deserves.
    map electric's Avatar
    map electric Posts: 3, Reputation: 1
    New Member
    		  
    #4

    Mar 14, 2009, 06:22 PM
    Quote Originally Posted by labman View Post
    I doubt the thermostat is the problem. You can easily verify that by jumpering the R and W terminals at the furnace. In heating mode, all the thermostat does is to connect them. If the blower still won't run, the problem is in the furnace. Quite often the relay done it, but your other info suggests the blower motor is dying. You have separate windings and relays for low and high speeds in auto and ON. Sounds like first the low speed winding died, and now the high is going too. You can check it again with a jumper from the incoming 120 volt black wire from the house to each hot lead of the blower motor. If the blower motor takes off and runs, turn you attention to the relays. Give the 120 the respect it deserves.
    What ever you do do not jumper r to w its r to g.
    map electric's Avatar
    map electric Posts: 3, Reputation: 1
    New Member
    		  
    #5

    Mar 14, 2009, 06:25 PM

    What ever you do do not jump r to w its g to r
Not your question? Ask your question View similar questions
 

Question Tools Search this Question
Search this Question:

Advanced Search

Add your answer here.


Check out some similar questions!

Lennox Furnace schematics [ 5 Answers ]

Hi, I need the wiring schematic for a Lennox forced air gas furnace Model #CH7D-51M. Thanks.

Lennox G12 furnace [ 3 Answers ]

Hello, My daughter has an old Lennox G12 furnace and the pilot light went out. I know this should be a simple task to relight, but we are not sure where the pilot light is and don't want to just stick a live flame in to "search" for it. Thanks, Chele

Lennox A/C unit won't run [ 4 Answers ]

Hey all, I'm hoping to get some pointers. I noticed last week that while the fan on the inside unit was running in my house, the outside Lennox (HL26 I think) was not running at all. I usually don't try to fix this kind of stuff myself, so I called a local HVAC/Electric company to come look at...

GMC Gas Furnace Fan Won't Run [ 3 Answers ]

Hi, I have a friend with a GMC gas furnace that will not start. We are receiving a three blinking LED code that says pressure switch failed to close. We found this switch on the main air fan and discovered the fan will not run in auto or manual. We checked for 120 VAC output on the circuit board...

Lennox oil furnace [ 3 Answers ]

What is the proper procedure for cleaning a oil furnace, such as cleanouts to heat exchangers and where could I find a exploded view of a lennox oil funace

View more questions Search