I have a 30+ year old forced air furnace. currently, when the thermostat is turned up to call for more heat, the burners ignite normally. when the heat exchanger-HE- gets to temperature (which seems to take a long time) the fan switches on normally.

HERE'S WHRE THE PROBLEM STARTS

The fan runs for approx. 1-2 minutes and shuts off. it repeats this continually, over and over. the burner does not shut down.

I believe the burner doesn't shut off because the thermostat is still calling for heat.
I also believe with all the on/off/on/off at some point the breaker trips. regardless, i have shut the furnace down before it can complete enough fan cycles to heat the house completely to the temperature the thermostat is calling for.

right now the fan limit switch has 3 temperature indicators settings visible.
let me describe:
1. it is a round silver (tin) disc with a temp. range at the bottom.
2. the three settings from low to high are 80F., 130F., and 205F.

My guess is 205F. is the HE limit. the the low limit is 80F. and the high limit is 130F.

what are the correct temperature settings for a fan limit switch. from low to high
(keeping it as simple as possible)


Thank you,


look forward to your answer, Egg

answers to your standard questions:

Manufacturer:

SUNBEAM

Model number may or may not be helpfull.
Age of equipment:

30+

Efficiency: Natural draft, 90%, 80%.

NATURAL DRAFT (PIPE TO CHIMNEY)

Plastic flue pipes are 90% Metal flue pipe and a draft inducer blower are 80% metal flues with no
draft inducer fan are natural draft.

Type of system:
Heat pump, hot water, forced air, etc.

FORCED AIR

Type of fuel:
LP, NG, oil.

NG

Tell us:
Does anything start. Any noises or blowers run when you turn it on?

DESCRIBED ABOVE


Try to turn fornace off and on at power switch or breaker.
Did this do anything?

YES. IT TURNS IT OFF AND ON NORMALLY


Modern furnaces will lock out, either whats called a soft lock out or hard lock out, if it detects a problem 3 times.
I hope this will help speed up the process of you getting a faster more accurate response.

NorthernHeat

Can you see the dial move back down after the fan starts? The first pin is fan off, set to 80, I usually set this around 95. The second pin is fan on, set to 130, I would try 140. And the tird pin is limit, safty off. Leave alone. The fan limit control could just be weak and in need of replacement. If in fact it is the fan limit turning the fan back off. Could the furnace be pulling unusually cool air from somewhere? The attic?

bharr07

you may also have a bad blower motor, this is why your motor is short cycling and tripping the breaker , and also check the cupped blower blades for lint build up after 30 years i can imagine what it looks like even if its not the blower motor , the blades should be cleaned for better air flow ,