combo fan and limit switch - Contractor Talk - Professional Construction and Remodeling Forum

02-08-2004, 04:29 PM

All right people I have a older furnace with a honeywell combonation fan limit sw model # l4064b2954.This unit is 1 year old.I replaced it prior because of no gas flow.Well I woke up this am and it was 12 degrees in the house.I have played with the sw and now things are working,but my question is what should the 3 on off switches be set at.Originally when i replaced the unit i just transfered the old unit settings.I live in central Alberta.The second part of my question.On a mercury sw thermostat two wire, how come you can see a spark from the glass bulb when you wiggle test it(normal current flow) but today i cant get any flash.Does this mean ive got a t-stat problem. Im an automotive tech by trade and I deal with a lot of auto electrical.Im kicking myself for not haveing my dvom at home.

Steve Wiggins · 02-08-2004, 05:06 PM

An improperly installed fan/limit switch can cause all the above problems. You should have your furnace checked by a professional for safety if nothing else. You definately don't want to wake up dead.

Bjd · 02-09-2004, 05:15 AM

Could you please give us a few more parameters in the type and the design of you furnace, as it a gas furnace or oil. Is it a conversion from gas to oil?
Natural draft or power vented? Does it have AC
Thanks
Bernie

02-09-2004, 11:19 PM

Its a gas furnace made by Furnace-Aire model # 125tc.
Way to big for a house,was told by the gas company guy last year its made for one of those small apartment blocks.125,000 btu's.forced air no ac.
Thanks

don-ohio · 02-14-2004, 03:29 AM

125K is NOT too big for most houses, ESPECIALLY where YOU live.Ha!.
This fan-limit switch......is it the really old type that the wheel has pointers on a temp scale and you set the pointers? Describe it. don-ohio

02-26-2004, 02:11 AM

The setting going clockwise are around 100,150,200 degrees.The first one is the temp the fan shuts off at the second is the temp the fan turns on at the third is the temp at which the burners shut off at to protect the furnace from over heating.The flash you see in the bulb in the tstat is because you are making and breaking a electrical circuit.ouch the battery positive and negitive terminals in a car you get the same results.No spark in the tstat could be a bad stat or if there is not a complete circuit to the furnace there is no spark.There maybe something else open in the circuit.