Old Lenox Furnace - request for assistance

[Bourbon Guy]

My elderly parents have an old Lenox natural gas furnace, ID 68-110-M-1, which was installed around 1964(?). Yes, they should replace it, but right now, in the middle of winter, they are having a problem. I live five hours from them and will be driving there tomorrow to get them some heat as their forecast is for single digit temperatures. But I would sure appreciate some professional advice before I take off.
Simply, the blower is not kicking on. All of the fuses from the main to the box/switch on the side of the furnace are OK. The unit has a standing pilot, which is lit. The gas valve opens when the thermostat calls for heat and the burners ignite. After a short time (90-180 seconds), the burners shut down. There is not an inducer fan on this older model, nor is there the newer control board. There are two items mounted on the plenum: A limit switch with two wires attached, and a unit marked "time" which contains two dials and has four wires attached. The blower is powered by a belt-drive Dayton 1/3 hp split-phase motor, model 6K0306. My dad thinks the motor was replaced some years back. He can't locate a wiring diagram in the furnace box or on the door.
Without being there, I can't check continuity on the switches or check the motor. Since I likely will be fixing this during non-business hours, I would like to take the parts with me that I need to repair the unit, or order them and have them shipped to my parents' house. What part(s) would most be suspect and needing replaced? Motor, run capacitor, limit switch, other switch, or something else? And do you know where I can get parts for a furnace this old? (or are there interchangable/universal parts that can be used?) Anyone have a wiring diagram?
I really do appreciate any assistance you can provide. I certainly am not an experienced HVAC tech, but with the right information I feel comfortable making repairs. Thank you.

[HayZee518]

first thing to check would be the plenum switch with the two wires. there is an aluminum dial when you take off the cover that rotates and makes up a set of contacts under the dial. there are two sliders to set minimum off time and on time. if basically is the proportional band the blower stays on. the other thing with a timer I have no idea what it may be - quite possible two of the wires operate the timer motor and the other two are from a switch. check to see if the plenum has any overheat "klixon" devices that might be connected to the control board for an overheat lockout.

[paul52446m]

My elderly parents have an old Lenox natural gas furnace, ID 68-110-M-1, which was installed around 1964(?). Yes, they should replace it, but right now, in the middle of winter, they are having a problem. I live five hours from them and will be driving there tomorrow to get them some heat as their forecast is for single digit temperatures. But I would sure appreciate some professional advice before I take off.
Simply, the blower is not kicking on. All of the fuses from the main to the box/switch on the side of the furnace are OK. The unit has a standing pilot, which is lit. The gas valve opens when the thermostat calls for heat and the burners ignite. After a short time (90-180 seconds), the burners shut down. There is not an inducer fan on this older model, nor is there the newer control board. There are two items mounted on the plenum: A limit switch with two wires attached, and a unit marked "time" which contains two dials and has four wires attached. The blower is powered by a belt-drive Dayton 1/3 hp split-phase motor, model 6K0306. My dad thinks the motor was replaced some years back. He can't locate a wiring diagram in the furnace box or on the door.
Without being there, I can't check continuity on the switches or check the motor. Since I likely will be fixing this during non-business hours, I would like to take the parts with me that I need to repair the unit, or order them and have them shipped to my parents' house. What part(s) would most be suspect and needing replaced? Motor, run capacitor, limit switch, other switch, or something else? And do you know where I can get parts for a furnace this old? (or are there interchangable/universal parts that can be used?) Anyone have a wiring diagram?
I really do appreciate any assistance you can provide. I certainly am not an experienced HVAC tech, but with the right information I feel comfortable making repairs. Thank you.

I believe the one marked time, 4 wires, is your fan switch. You will have one hot line going to it and one line going from it to the blower. The other two wires will be low
24 volt wires and they make a heater switch, which takes about 60 sec. to
heat up and start the blower. Is this a up flow or down flow? They still make
fan switches with heater in them, if you can find a dealer that has them.
When the thermostat call for heat the fan heater switch is energized and that is what starts the blower, after it heats up. later paul

[Bourbon Guy]

Paul...you asked if this were an up or down flow furnace. The unit is in the home's basement, so the heat is forced up and the return air flows downward. Is that considered an up flow or down flow?
In the event their is no availabilty of the old-time fan switch that creates heat to start the blower, is there a down side to installing a more conventional fan switch ... other than some cold air being pushed throught the duct work upon start up?

Thank you to both Paul and Hay Zee for sharing yoru knowledge.

[paul52446m]

Paul...you asked if this were an up or down flow furnace. The unit is in the home's basement, so the heat is forced up and the return air flows downward. Is that considered an up flow or down flow?
In the event their is no availabilty of the old-time fan switch that creates heat to start the blower, is there a down side to installing a more conventional fan switch ... other than some cold air being pushed throught the duct work upon start up?

Thank you to both Paul and Hay Zee for sharing yoru knowledge.

That is a basement model. Honeywell makes a fan a limit that goes into the hot air plenum, and you can get it with a heater switch in it. You can get them in either a 8" or 12" stem. later paul

[Bourbon Guy]

Thank you again for your insights Paul and HayZee. As an update, it turns out the blower motor was the problem. I started checking each of the components (as you had recommended) and went down my list. Because it had been replaced some years ago, the motor was last on my list to check, but it was the culprit. Finding a replacement and swapping out was an easy task. As a tip to others, the black and red wire connections (typically) inside the cover plate control the starter windings on a split phase motor. Reversing the position of these two wires changes the direction the motor turns.
So, a new motor, a new belt, everything greased and oiled, and a new filter and my parents should be set for the rest of the winter. I wish they would take advantage of the rebates and offers to obtain a more effecient system, but it just isn't to be right now.
As a side note, I did find a universal replacement Honeywell fan/limit switch available through Grainger. They had replacement motors too, but we bought from a local business.
Thanks again guys! I really appreciate the service you provide to do-it -yourselfers through this forum.