Need help 20 year old furnace

First off I did a search in the forums first before posting, no luck on my problem. By the way the forum looks great.
I have a DM-OLSEN natural gas furnace model HBS-105-5 forced air Im guessing about 20 years old. So here is my problem, the pilot light is working but the furnace wont start. I can hear the Hunter thermostat send the signal to the furnace but it wont fire up. I have replaced the thermocoupler it seemed to work better for a few days but now Im back to the same situation. The funny thing is the only way I can get the furnace to work is to turn on the fan manually and turn it off 3 times then it lights up. Any ideas?

Thanks in advance
Fres

 

If turning the fan on & off (via the thermostat?) makes the furnace come on, I suspect you have a thermostat problem. An easy way to check is remove the wires from the stat, writing down which wire goes to which terminal, & hook the wire from terminal RH to the wire from terminal W. If the furnace fires, replace the stat. I do not advise using Hunter. They have the worst reputaiton in the industry. White-Rodgers or Honeywell are the two best.

 

Sorry to mislead you, when I turn on/off the fan via the switch on the furnace itself. So in otherwords when the furnace quits I go into the basement and press the button for the fan and turn it off 3 times then it fires up the burners. Then the furnace will function as intended. Could it be the limit swt? The on/off swt for the fan is on the same control as the limit swt. It looks like it has three setting on a dial on the limit switch, one is set at about 80, the middle one is at 105, and the last one is at 200.

Thanks alot Grady
fres

 

Honestly, I have never encountered nor heard of such a thing. Obviously, I'm guessing but there may be a second limit somewhere in the furnace keeping the gas valve from opening. Another possibility is the fan & limit control (the control with the manual fan switch) is somehow malfunctioning. Sorry I can't pin it down any more but you do have a strange one on your hands. Once you get it fixed, please post back with the cause.

 

The fan/limit you describe sounds like a honeywell L4064...Is it possible one of the wires on the limit side is loose and when you move I'm guessing the "fan on" stem of the control you are just wiggling the wire and it makes contact???

 

Yes it is the L4064 I will check the connections, this could be it! Last night it failed when I was at work it was 13'C in the house very cold outside. There is 3 adjustments on the dial what should they be at? Thanks grady & mbk3 will post back

Thanks for the help
fres

 

Settings should be 95.......130.......180 These are generic settings..your furnace may need fine tuning..

 

Thanks alot (Grady/mbk3) I went out and got a new limit switch $70 not bad. It seems to work so far we will find out tonight when the wood stove burns out. The old switch didnt seem to operate smoothly like the new one, the old one was jerky when it was turning. Well I hope this works, I will post back in afew days to let you know.

thanks so much
fres

 

its a 100% I cant that u guys enuff

thanks
fres
:wmann3: