Furnace clicking noise, blower runs continuously

Spydey · 01-06-2013, 06:55 AM

I just replaced the blower motor on an old Lennox forced air furnace and now the blower runs continuously while the burners cycles on and off. When the thermostat is satisfied, I can hear weird clicking noise, then I can hear burners shut off for several seconds. The clicking noise starts again and then the burners fire up. After a min or so the cycle starts again. The clicking sounds like an electrical shorting type noise. If I turn the thermostat down the blower will shut off but will not fire up again till I turn the thermostat up. There's 2 separate limit switches. One is a fixed limit switch and the other is a fan control. Would both of these switches be faulty? Any help would be appreciated. Attached are some pictures of the furnace, which is a Lennox.

The clicking seems to be coming from the gas valve looking component where the thin copper tubing is connected. The tubings are part of the flame sensors.

scottmcd9999 · 01-06-2013, 07:32 AM

Can you show a pic of the blower motor and wiring?

Is there air conditioning on that beast?

Spydey · 01-06-2013, 07:47 AM

The furnace seems to stop cycling right now and I don't hear the clicking. The burner just came on again and I heard a slight click but the blower hasn't stopped. Below are the pics of the blower motor and the wiring leading to the fan limit switch. There's no AC on the furnace.

**beenthere** · 01-06-2013, 09:20 AM

The copper line goes to a reg, doubt its making the clicking noise. probably either the gas valve or the limit.

Are you sure the blower motor is spinning the right way.

Spydey · 01-06-2013, 09:40 AM

Quote:

Originally Posted by beenthere

The copper line goes to a reg, doubt its making the clicking noise. probably either the gas valve or the limit.

Are you sure the blower motor is spinning the right way.

I'm leaning towards the limit. Yes, the motor is spinning the correct way. I know because there's heat blowing out of the vents. I cleaned the pilot and flame sensors with a scotch pad, wonder if that had anything to do with it.

You think its the fixed limit or the fan limit? If either one is faulty, would it cause the symptoms the furnace is having?

**beenthere** · 01-06-2013, 09:46 AM

Probably the limit.

Is it blowing out as much air. more air, or less air then the old blower motor.

A motor spinning backwards will still blow out air.

Spydey · 01-06-2013, 09:59 AM

Quote:

Originally Posted by beenthere

Probably the limit.

Is it blowing out as much air. more air, or less air then the old blower motor.

A motor spinning backwards will still blow out air.

There's only 2 wires on the motor to change the rotation and the diagram says to interchange the wires to reverse rotation. I left the wires in its factory state when I first installed the motor and it was spinning the wrong way because very little air was coming out of the vents. So I interchanged them and now its spinning the right way.

The circled prongs in the photo is where the 2 rotation wires go. The other 2 wires in the photo attached by the nuts, I guess, are the power wires. I interchanged them once to see if that changed anything but it did not so I connected them the same way as the old motor.

Which limit? The fixed or the fan?

**beenthere** · 01-06-2013, 10:09 AM

Fixed. The fan switch/relay, is not a limit per say.

Spydey · 01-06-2013, 10:11 AM

Quote:

Originally Posted by beenthere

Fixed. The fan switch/relay, is not a limit per say.

Ok, thanks a lot for the replies and advice. I'm gonna take the limit switch out and check for continuity.

**beenthere** · 01-06-2013, 10:15 AM

Probably won't tell you much. Unless the contacts are pitted or carboned up.

Limits may be weak and opening early. Is the air coming out of the registers hotter then it use to be, or about the same or cooler. the limit may have become weak from when the old motor stopped working.

Spydey · 01-06-2013, 10:27 AM

Quote:

Originally Posted by beenthere

Probably won't tell you much. Unless the contacts are pitted or carboned up.

Limits may be weak and opening early. Is the air coming out of the registers hotter then it use to be, or about the same or cooler. the limit may have become weak from when the old motor stopped working.

Air seems to be about the same as before. You might be right about the limit becoming weak because I noticed yesterday that it ran like it was suppose to for a short time. Seems the limit hasn't completely failed just yet. I should just change it as it's not a very expensive part and see if that fixes it.

**beenthere** · 01-06-2013, 10:35 AM

Yep, they're cheap parts.

Spydey · 01-06-2013, 10:39 AM

Quote:

Originally Posted by beenthere

Yep, they're cheap parts.

I'm still wondering about the blower running continuously. Would a faulty limit cause that also?

**beenthere** · 01-06-2013, 10:46 AM

No, that would be the fan switch on that furnace.

Spydey · 01-06-2013, 10:56 AM

Quote:

Originally Posted by beenthere

No, that would be the fan switch on that furnace.

Ok, so you think both my switches are faulty? The fan stays on continuously while its doing the whole clicking and cycling thing. The fan will only turn off when I lower the temp at the thermostat. The furnace doesn't seem to turn back on until I raise the temp at the t-stat. Basically I turn up the t-stat to just under 70 and I can hear the burners light, then the blower comes on and it will stay on constantly. When the t-stat is satisfied, the rapid clicking starts and the burners shut off for a few seconds and then I hear the rapid clicking again and then the burners fire up again. Burners stay on for about a min or less and then the hole cycle repeats itself with the clicking each time before the burners light and just before they shut off. During this cycling the blower is on constantly until I turn the t-stat down to about 60 and then the blower will shut off after about a min or two. At 60 or slightly above the furnace doesn't start again on it's own it seems. But if I turn the t-stat up a little it will fire up again.