I went down and opened furnace, Combustion blower was running, checked pressure switch with ohm meter, switch was closed. Pilot not lighting.
This is 10:00 at night, did not know what else to do. (Used to work as auto mechanic, sometimes taping a component would get car to start, or motor to falter, depending on suspect component.
Anyways, tap on board,(RobertShaw SP735A)lightly with stick. Tic-Tic-Tic-Tic-Tic-Tic- goes the igniter, pilot is lit, click-click-click goes the gas valve, burner lights, have heat rest of night. Next day SOS. Order new robertshaw SP735A, while I'm at it the other thing this furnace always did, was as soon as the T-Stat call's for heat the blower-fan always started right away. Furnace would cycle,(normal length of time) shut off, 10 seconds or so later fan kicks back on for about 1 minuet, shuts off till next heating cycle.
Suspect limit control, remove cover, find wire on left side burnt about 1/4" from switch, remove limit control, fix wire, same old story.
remove limit control again, open switch find contact points on that side(left as looking at it)burnt, find points staying open, switch arm not moving.
OK bad limit control.
Replace board and limit control, burners lighting all the time OK, fan still coming on from "get go"(manual/auto, on new limit control set to auto, Auto/fan on, set to Auto at t-stat also)
I left the hi-low voltage break-away tab in place, as that's the way the old one was.
Three wires total on this limit control, blue upper left, red upper right, black bottom.
Furnace (burner and fan) will run for a while, burner will kick off, (blower still running)
"Seems" to kick off(burner) at point when limit control should turn fan on.(I have it set to 120)
Waite a while watching limit control, almost to fan off point, burner will kick back on.
Looking at wiring diagram that came with new limit control upper left is fan control.
If I turn off furnace, disconnect blue wire, turn furnace back on; fan still starts from get go. There is 120Volt at disconnected blue wire with furnace running.
I wonder if its possible that the blue, (upper left) and red,(upper right may be reversed it the junction box?
Or other wise wired wrong? Or possible bad relay?
Furnace is warming house, thermometer in T-Stat even with set point, but this system is running almost constantly. Will shut off, (fan and blower) then less than a minuet later back on. Seems this system is running WAY TOO MUCH.
It is cold ~ 15 degrees, but this still seems like system is running too much.
Any thoughts, (Other than calling a repair tech) appreciated.
SWMBO say's it's coming on,and heating the house,so it's OK, and does not want to put any more money into it.