2008 Armstrong Air Furnace Blower Not Starting

[Jimhefel7]

Gas valve is on, batteries in thermostat are new. Pressure switch lines and ports have been checked and are clear. Water drain pan and line are verified clear. I could be wrong but I thought that the first event in the sequence for the furnace to fire was the blower starting up, and that is not happening so I was not expecting to see the igniter glow, and it does not. When I turn on the Tstat it signals the furnace and the furnace clicks and then sounds like it is trying to start up, but only hums. It sounds like it is a seized motor, but the blower starts up fine when the A/C is turned on, it is only when trying to fire up the heat that the blower is not starting. Here is the exact sequence.

1. Thermostat is turned on and can hear the switch click at the thermostat.
2. Furnace receives signal when tstat is turned on and clicks at the furnace.
3. Furnace hums as though it is getting juice and trying to start.
4. Red LED comes on on the little circuit board and stays on for a couple seconds.
5. Red LED goes off for a couple seconds, then blinks 3 times.
6. Red LED continues to blink in clusters of 3 times.
7. Furnace continues to hum as though it is trying to start but nothing fires and no blower comes on.

Whatever switch or relay or solenoid or capacitor that controls the blower kicking on during the heat function I assume is my issue, but not sure. Wondering if there is a quick way to check this. I have a multimeter on hand at home. Hope some of this info helps. As far as exact make and model, I would have to give that info when I get home, I'm at work now.

 

[Reach4]

I don't know your furnace. Is this one where the combustion air comes from outside and the blower you are referring to is the little blower for the combustion air? Or are you referring to the big blower that blows air through the house? That big blower only goes on once the flame has made the air area hot.

Does your furnace have an automatically lighting pilot light? I expect so. The pilot light will have to light before the big burner goes on.

 

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[Jimhefel7]

Hmmmm, I don't believe the combustion air comes from outside. It is a glowing ignitor not spark or pilot. In the past when it worked, the blower was the first thing to go on, then the ignitor, then there was flame and heat. Now the blower does not kick on, so there is no igition and no flame. I'm assuming there is a relay that kicks the blower motor on. The blower motor works fine for the A/C just not the heat, so I was assuming that there are two relays, one for the High speed (A/C) and one for low speed (heat), and I figured the relay that starts the low speed is bad. Just wondering if I am correct in that there are indeed two separate relays, and if so, how to go about testing the relay to see if it works. Don't know an awful lot about furnaces, just from what I've read up on.

 

[Jadnashua]

The hum could be the gas valve trying to open. Your furnace probably has a flame detection sensor, and the red flashing light is probably indicating that the flame was not detected. No flame, no blower. Do you ever see the flame coming on? Many furnaces do not turn the fan on until the heat exchanger is at least warm, otherwise, it can be uncomfortable blowing cold air.

You answered while I was typing, so I'm adding a bit more. If you don't have the manual, look online. But even then, there's almost always a wiring diagram inside of the thing on one of the removable panels. Sometimes, they're a little hard to figure out, but if it's an interlock, you should be able to isolate it. That may also have the error codes listed for the flashing light.

 

[Jimhefel7]

Yeah, I think I'm going to tackle this when I get home, I can't do much from work. Was just trying to find out if there are typically separate blower motor relays for heat and A/C and how to test them.

 

[Jimhefel7]

Apparently the 3 flashing LED signals a "pressure switch open with inducer on" hopefully this helps.

 

[Jimhefel7]

I don't know your furnace. Is this one where the combustion air comes from outside and the blower you are referring to is the little blower for the combustion air? Or are you referring to the big blower that blows air through the house? That big blower only goes on once the flame has made the air area hot.

Does your furnace have an automatically lighting pilot light? I expect so. The pilot light will have to light before the big burner goes on.

The combustion air inducer is not starting, yes, you are correct, this is the "blower" I was talking about, sorry not the main blower. The combustion air inducer has to start before the ignitor will light correct? The three flashing LED's indicate "pressure switch open with inducer on." If the air inducer is not running, the inches of water column to the pressure switch will be such that it will not turn on (close) correct? I am assuming that there is power to the air inducer so the unit thinks it's on, but the hum is the motor trying to run and it is seized up for some reason, so it is throwing a code for the pressure switch when in fact it is a seized air inducer motor. I am not at home now so cant check if the motor turns freely but does this sound like it makes sense?

 

[Reach4]

I am assuming that there is power to the air inducer so the unit thinks it's on, but the hum is the motor trying to run and it is seized up for some reason, so it is throwing a code for the pressure switch when in fact it is a seized air inducer motor. I am not at home now so cant check if the motor turns freely but does this sound like it makes sense?

I don't know those. But generically, does that motor have a capacitor? If so, that starting capacitor may be bad. If the motor is just a 2-wire device, I would try to see if voltage was being delivered to the motor. Voltage but no rotation would seem to point to a failed motor.

 

[Jimhefel7]

Ok, when I get home I will check for voltage to the motor. If there's no voltage, that must be a bad capacitor or relay, which is what I was trying to get at but my knowledge and vocabulary pertaining to furnaces is limited so I was pretty unclear. If there is voltage to the motor, then it must be a bad motor. I will give a look see if the motor spins freely and check for power to it and get back to you. Thanks for the help and pardon my ignorance.

 

[Jadnashua]

If that fan is not turning, you need to find out why. But, if it is, there could be a bad vacuum sensor/pressure sensor, a cracked fitting or split hose going to it, or a bad or corroded contact, or something is blocking the air intake sufficiently to restrict air movement. The interlocks should be shown on the wiring diagram. To verify, you may be able to momentarily bypass the suspected switch/sensor with a jumper, but if you are not comfortable with this, hire a professional. Usually, the interlock uses 24vac, but not always.

 

[Jimhefel7]

Well, I found the problem. A sparrow flew in my combustion air vent and made its way all the way to the combustion air inducer blower impeller and lodged itself in there and seized up the impeller. The thing was completely mummified. Put it back on and it fired right up. Sucks to be that bird.

 

[Reach4]

Nice. Well done -- I mean you-- not the bird.

I presume you are going to add a course screen to keep future birds out.

I was troubleshooting and tracking voltages in a gas dryer that would not keep its gas open. I found a bird nest and two crispy birds. I had the old single-flap exhaust, and replaced it with the newer 4-flap model that does not let birds in.

 

[Jimhefel7]

Hahah yeah it didn't go so well for the bird.

I'll look and see what I can find. I've got to get a coarse screen to put around my fireplace exhaust as well, birds nested in that thing the past two years. That was a little more obvious though with a bunch of grass and feathers stuffed in it. Would like to find something either plastic or coated for the combustion air pipe so it doesn't rust. Just glad that it was a quick fix and didn't cost anything. I think I spent about 4 hours searching, reading, and researching, then spent about 15 minutes on the furnace itself. Thanks for the help.

 

[Reach4]

Take a look at the aluminum mesh made to mount atop gutters.

 

[Jadnashua]

Whatever you use, you don't need or want something that has a fine mesh or covers very much surface area...some of those air intakes on gas appliances are really picky about air flow.

 

[Jadnashua]

Whatever you use, you don't need or want something that has a fine mesh or covers very much surface area...some of those air intakes on gas appliances are really picky about air flow.