This article describes steps taken by an InspectApedia reader to diagnose and fix a blower fan that would not start when it should, accompanied by tracking down the source of a buzzing noise.

Bad Furnace Blower - Buzzing Circuit Breaker?

This Q&A with InspectApedia.com Marty describes a sequence of steps in diagnosing a heating system blower fan that was not working but produced buzzing noises traced to the circuit breaker.

On 2022-03-22 by Inspectapedia Com Moderator - Furnace wouldn't shut off and then wouldn't turn on and there is buzzing at the breaker

@marty,

Reviewing a bit:

• Watch out: Buzzing at a circuit breaker could indicate a defective/unsafe circuit breaker or panel: what are the brand and age of your electrical panel?
  
  Don't ever ignore a buzzing or hissing, arcing, spitting circuit breaker as the risk is an electrical fire. Turn off the circuit.
• Buzzing at a control relay on your heating or air conditioning system blower unit often indicates a failing relay on a control board or a failing low-voltage transformer.
• Buzzing or more-likely humming noise at the blower fan motor could indicate a bad start capacitor.

Any of those defects can explain the failure of an HVAC blower fan to start when it should. At the end of this page we list other buzzing noise and blower-fan diagnosis and repair articles you'll want to review.

Be sure to confirm that power is being delivered where it should be: if you don't know how to use a DMM or VOM to do these tests you really need onsite help from a service tech as you could be shocked or killed if you make a mistake.

There are usually 1, sometimes 2 transformers on heating systems in general:

The low voltage 120v to 24VAC transformer powers the thermostat and sometimes a control board or relay at the heater

On oil burners a high voltage transformer makes spark that ignites the oil flame.

On an electric furnace the transformer ought to be only addressing the thermostat. The fan normally would be a 120VAC device, though a control board and relay operating the fan might indeed use the low voltage circuit.

In general, if an electric furnace heating element doesn't work and doesn't heat the air in the plenum, then the fan wouldn't come on.

The starting problem: that the furnace would not turn off even when the thermostat was satisfied, would lead a tech to check that the furnace thermostat is properly wired and then to replace the fan limit controller.

If in doing those steps there was a wiring error or an error that blew a fuse that'd prevent the heater from working afterwards.

On 2022-03-22 by marty - I suspect a bad/wrong new sequencer.

@Inspectapedia Com Moderator, Thank you for all of your input, this has been the only help I've found.

I was thinking.. if the transformer was bad, would that cause the fan to not turn on?

Example: it had enough juice to power the fan(in fan only) OR to power the heating element, but not both at the same time), or would nothing work at all if the transformer was bad?

That's why I keep circling back to bad/wrong new sequencer.

On 2022-03-19 by Inspectapedia Com Moderator - snap-disc fan limit replacement didn't fix fan problem

@marty,

I agree it's a frustrating diagnostic problem - and apologize that we can't be smarter from our remote spot relying just on text.

It's worth checking that your wires and connections are all intact and correct.

On 2022-03-19 by marty - replacing the fan limit control didn't help

@Inspectapedia Com Moderator, I just replaced that, and it did not work. I'm out of options. I've replaced the sequencer, the breaker, all 4 fuses, and the 2 fan limit/discs(of which I've had 3 different double stack discs on there) The only thing I've not changed is the transformer and capacitor. To my knowledge, there is no control/circuit board.

The furnace heats up, so the thermostat is working as its sending signal to warm up. The fan works when turning the switch on the unit itself(there is no 'fan' option on the thermostat)--so I'm ruling out the motor to the fan and capacitor.

Unless the new sequencer is bad, not compatible, or I've mis-wired something, I'm out of options.

The last time it tried to work correctly, it heated up and then acted like it had tried to start the fan but didn't complete the crank and gave up. That is before I changed the breaker, and it wouldn't even turn on in FAN mode.

On 2022-03-13 by Inspectapedia Com Moderator - identify the type of fan limit control - dial vs snap-disc

@marty,

OK;

I asked because if it was a dial type fan control you could watch the dial turn in response to heating of the supply plenum air and that'd be diagnostic.

With a snap-disc limit control all you can do is confirm that the burner runs and the air in the plenum gets hot and the fan isn't coming on in response to temperature.

If you establish that the fan will run manually then that points to a bad limit disc controller - it's a small and inexpensive next step. Try swapping in a new one. Be sure you're using the manufacturer's specified operating temperature range.

On 2022-03-13 by marty - I replaced one of the snap-disk fan control switches

@Inspectapedia Com Moderator, it's a disk.

I've changed one of them because it was cracked, but it has a smaller one I've not replaced yet. The diagram from the manual says "Limit, D.P. and Limit, S.P." which I assume stands for Single Pole and Double Pole.

On 2022-03-13 by Inspectapedia Com Moderator - is there a dial type fan limit control you can watch?

@marty,

Is there a fan limit control with a dial you can watch or is it controlled by a snap disc?

For a review of diagnosing your original problem: the furnace wouldn't turn off, see

• BLOWER FAN WONT STOP - LIMIT SWITCH
• BLOWER FAN WONT STOP - THERMOSTAT SWITCH
• HEAT WON'T TURN OFF
  

On 2022-03-13 by marty - original problem was furnace blower would not turn off

@Inspectapedia Com Moderator, I completely understand it was confusing. The original problem was the furnace kept running well after the desired temp was reached, and would only stop by turning off the breaker.

After replacing the thermostat on the wall, the limit switch, 2-60 amp fuses, main breaker for it, and the sequencer; the problem is now the elements do turn on, but the fan does not. The fan will work in 'FAN' mode on the unit, so the fan works/is getting power.

On 2022-03-13 by Inspectapedia Com Moderator - furnace blower fan won't kick on when thermostat set to higher temperatures

@marty,

When we have a furnace fan that works OK until the thermostat is set to a higher temperature I suspect that the longer on-time at the furnace (to meet the higher temperature demand at the thermostat) is causing a furnace component to overheat.

At the FAN-OFF-LIMIT upper end of a heating furnace limit control operation the system will turn off completely to avoid over-heating and damaging the plenum (dangerous risk of CO leaks into building air).

At the FAN-ON end of a heating furnace fan control, the blower will turn on once the plenum temperature has reached the FAN-ON temperature (thus avoiding blowing cold air on building occupants)

I confess the range of observations and comments in your question make me a bit confused but I can offer some general explanation that might be helpful.

Higher amperage fuse on an electric heating system usually are controlling individual electric heater elements

Voltage Transformer found on a heating system is usually converting 110 volts to 24 volts that is internal used to power controls such as a wall thermostat.

Keep in mind that most heating furnaces will not turn on the blower until the air in the supply plenum is sufficiently warm because the system doesn't want to blow cold air on the occupants.

So if your electric heater elements are not turning on then the blower would probably not turn on.

While you pay the Valiant effort to fix your heating system at this point it would probably make sense to bring in a trained heating professional who's familiar with working on electric furnaces.

On 2022-03-13 by marty - Intertherm furnace fan won't work at high thermostat settings - shotgun blast of possible causes

I apologize in advance for the long question..

I've recently had trouble with my electric furnace. It's an older heat-only Intertherm furnace. I was originally having trouble with it in regards to it not shutting off. If the thermostat on the wall would be set to 65 degrees, it would kick on and off like normal.

However, if it were to be set on 68 or higher, the furnace(heat and air), would not kick off well after it was past 70 degrees and could only be turned off by flipping the breaker.

So originally, I bought a replacement fan limit switch, thinking that was the problem as the old one looked damaged. It still continued running for long periods of time after I replaced the limit switch. I then replaced the 2 60-amp fuses, due to them being old and one looked slightly scorched (I do not have an electrical voltage/ohm/amp meter of any sort and fuses are cheap to replace).

The unit also has 2 smaller 30-amp fuses, also older, that I have not replaced yet. That resulted in no change in how the furnace acted.

Then this week, the furnace simply would not come on at all. The breaker was not off or kicked, so I changed the breaker--I would sometimes hear buzzing coming from the breaker when the furnace had been on a while-right before I turned it off. I thought the breaker could have been going bad anyway. The breaker and furnace were the same age, 35 years.

It then worked like it had been.. running for long periods of time if the thermostat was set at 68 or higher, and 'normal' if it was set lower. But then it quit working again. So I replaced the sequencer.. it's not an exact match part, but I'm fairly certain the wires are matched up to what they should be from the old part.

Still not running---however, when I turn the switch on the furnace to 'FAN', the fan comes on.. and when I adjust the thermostat to make the furnace come on, the heating elements come on also.

I can see the glow emitting from the elements and feel the heat. The fan itself isn't coming on now when set to 'AUTO', but the heat works.

I'm running out of options of what to replace. The 30 amp fuses, the transformer, and the fan capacitor are the only things left I can think of.

The fan works, so I know it's not the blower motor, and I'm fairly certain it's not the capacitor or the fan wouldn't even work in FAN mode, right?
I have no idea what the transformer or 30 amp fuses do. Unless I've somehow miss-wired it or a part I just replaced is already faulty, I'm out of options.

 

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Continue reading at BLOWER FAN WONT START, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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• HUMMING NOISES in BUILDINGS - topic home
• LOW VOLTAGE TRANSFORMERS, TRANSVERTERS, CONVERTERS
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• RELAY CONTROL SWITCHES - causes of chattering humming or buzzing relay controls

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