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Old 03-04-2012, 04:02 PM   #31
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Proper ignition/blower sequence in older gas furnace?


Yer Welcome. And get 2 new CO detectors for your house. 1 for your bedroom and 1 downstairs.

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Old 03-04-2012, 05:31 PM   #32
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Proper ignition/blower sequence in older gas furnace?


Very good suggestion. I do have one in the living room that I installed when I put a woodburning hearth stove in my fireplace slot. I ought to get another for the other end of the house.

Incidentally, this little digital kitchen thermometer has come in so handy since I bought it three years ago for about 10 bucks. Nicely built and seems very very accurate.

I was pleasantly surprised at how accurate the markings on that fan switch dial turned out to be. The digital unit's probe extends into the furnace cavity about four inches through an empty former screw hole.


It's interesting to watch the readout as the furnace cycles. As soon as the blower starts the temp begins to drop but the fan switch dial continues very slowly upward for another minute before ever so slowly going down again. The bulk of the bimetal coil and it's metal housing stores enough heat to make it pretty slow to responsive. For the purpose it's doing its job just fine though.

Last edited by frascati; 03-04-2012 at 05:37 PM.
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Old 03-04-2012, 06:19 PM   #33
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Proper ignition/blower sequence in older gas furnace?


While that burner was out, did you get a chance to get a light & mirror in there to check out the exchanger?
If your furnace temp is not rising above 175F while running, I'd leave the pulley sizing as it is for the quietest possible operation. If your furnace does run hot then a split pulley will give a wider range of options but will probably also involve a motor position adjustment, fan limit nib position changes, possible belt change and more noice.
I/4 hp will do for a straight motor swap out. Because of the age of this unit, watch that the spiral wire cover connections are really solid or that the motor wiring includes a ground line.
If the furnace does run hot then you should let us know before you choose a new motor.
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Old 03-04-2012, 07:31 PM   #34
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Proper ignition/blower sequence in older gas furnace?


No, the furnace, according to my digital thermometer never exceeds 135 degrees. I'll leave the pulley in place. I don't believe that overheating was ever actually the issue here. That upstairs thermostat "heat anticipation" setting was always too low and the burner never stayed on long enough to overheat.

However, since I posted last, and for the first time in two days, the motor balked and hummed and refused to start. Guess the starter winding has just had too much. I was resigned to replacing it, but was hoping against hope that all my adjustments (knowing full well that they had nothing at all to do with the starter switch and windings on this motor) might have put me in good graces with this old furnace sufficient to have it pay me back. Of course that was misplaced hope. Of course I'm going to replace the motor. Just sayin.

So tomorrow it's off to Grainger or Holland Electric Motor to get a 1/4hp replacement.

While I'm here, let me pick the brains a bit more. That Leeson 1/4hp high efficiency motor I listed ...
http://attachments.temcoindustrialpo...M090602.00.pdf
...is spec'd to run at half of the amperage of the motor I presently have. It's described as split phase start, capacitor run. I cannot find a good description of this in the online tutorials. I had thought that the presence of a capacitor hump on the body of the motor indicated an improved starting torque, but it is for 'run' only and not for start. I'm learning more about electric motors this week than I ever thought I would. Apparently, the capacitor on a capacitor start motor does not supply "oomph" from stored energy so much (as I'd always supposed it did) as it merely induces the motor to the optimal phase angle. That's beyond my ken, but I'll accept it. In other words, adding a start capacitor to a split phase motor would accomplish nothing since the windings are not set up for it in the first place.

So what is the advantage of purchasing a "capacitor run" motor like the one I listed? Other than the obvious in this case.... higher running efficiency.

Last edited by frascati; 03-04-2012 at 07:34 PM.
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Old 03-04-2012, 07:54 PM   #35
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Proper ignition/blower sequence in older gas furnace?


Quote:
Originally Posted by biggles View Post
if the stat is calling heat the burner always runs...the supply fan is the last thing to come on and the last thing to go off....that Honeywell limit controller should be in the heat exchanger area not the plenium.it need to see the heat asap to react either it be fan ON or Hi limit for burner
Can't. The radiant heat would peg the limit.
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Old 03-04-2012, 08:05 PM   #36
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Proper ignition/blower sequence in older gas furnace?


Quote:
Originally Posted by frascati View Post
No, the furnace, according to my digital thermometer never exceeds 135 degrees. I'll leave the pulley in place. I don't believe that overheating was ever actually the issue here. That upstairs thermostat "heat anticipation" setting was always too low and the burner never stayed on long enough to overheat.

However, since I posted last, and for the first time in two days, the motor balked and hummed and refused to start. Guess the starter winding has just had too much. I was resigned to replacing it, but was hoping against hope that all my adjustments (knowing full well that they had nothing at all to do with the starter switch and windings on this motor) might have put me in good graces with this old furnace sufficient to have it pay me back. Of course that was misplaced hope. Of course I'm going to replace the motor. Just sayin.

So tomorrow it's off to Grainger or Holland Electric Motor to get a 1/4hp replacement.

While I'm here, let me pick the brains a bit more. That Leeson 1/4hp high efficiency motor I listed ...
http://attachments.temcoindustrialpo...M090602.00.pdf
...is spec'd to run at half of the amperage of the motor I presently have. It's described as split phase start, capacitor run. I cannot find a good description of this in the online tutorials. I had thought that the presence of a capacitor hump on the body of the motor indicated an improved starting torque, but it is for 'run' only and not for start. I'm learning more about electric motors this week than I ever thought I would. Apparently, the capacitor on a capacitor start motor does not supply "oomph" from stored energy so much (as I'd always supposed it did) as it merely induces the motor to the optimal phase angle. That's beyond my ken, but I'll accept it. In other words, adding a start capacitor to a split phase motor would accomplish nothing since the windings are not set up for it in the first place.

So what is the advantage of purchasing a "capacitor run" motor like the one I listed? Other than the obvious in this case.... higher running efficiency.
If i was you i would buy a 1/3 hp, For that type furnace a never stocked a 1/4 hp. If you was to check the amps with that size blower
you are are probably close to pulling too many amps all the time. You can buy a 1/3 hp ,same mount, same rpm and it will not over amp. Paul
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Old 03-05-2012, 06:32 PM   #37
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Proper ignition/blower sequence in older gas furnace?


Well, for the time being I think I'm ok. I'll post the following for the off chance that anyone else finds themselves here with a similar malfunction.

And incidentally, this really does seem to be a very good value for a belted furnace blower replacement motor...
http://www.electricmotorwholesale.com/LEESON-M090405/

Runs at nearly half the amps as similarly rated motors. It's about six lbs heavier than others as well. The website suggests that this is in sturdier end castings and higher copper content in order to meet efficiency goals.

Anyhoo..... before clicking on "put in basket" at that site I decided, since I'm such a cheap bastard, but just as much because I hate to give up, to remove the motor, put it on the bench, and cycled it over and over and over until I could get it to balk. Just when I was beginning to think it was only going to do so under load.. it balked. It just sat there and hummed. Peering into the vents I could make out that the centrifugal swash plate was stuck.

I took the rear end off and looked into things closer. The swash plate is driven by two stamped metal flying weights held in place by two springs. When fully extended under high rpm the whole mechanism is so extended that it puts very tiny pressure against the plastic swash plate. It is that pressure that starts the plate back on its way to closing the starter contacts when rpm drops. My mechanism was exerting almost zero pressure against the swash plate at full extent. Seriously. This was the only thing wrong. The springs are mounted on four tabs on the arm weights. I bent each tab every so slightly backward, thereby exerting a tiny bit more, but substantial, pressure on the swash plate at full extent. Anyone remotely familiar with this mechanism can picture this.

Put everything back together. It's been running without a hiccup for over 24 hrs.

There's nothing wrong with the contacts or the windings. The starter contacts were often not closed when they were needed. The humming was the motor trying to start via the run windings alone. Without the starter windings, these windings, literally, didn't know which way to turn These windings are much more robust than the starter windings so probably didn't suffer any damage from this. Just shut off the overload switch. A couple of such cycles were sufficient to nudge the rotor and snap the swash plate back against the starter winding contacts and presto, it would finally start. Meanwhile, when the starter contacts were suddenly brought together under current, a condition they weren't designed for, they flashed and started breaking down.

So all's well for now. I only saved 160 bucks, but the feeling of triumph is priceless.

I'll just put that 160 toward a new furnace in a few years.

Thanks again for the advice and the fun here.

Last edited by frascati; 03-05-2012 at 06:38 PM.
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Old 03-06-2012, 07:26 AM   #38
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Proper ignition/blower sequence in older gas furnace?


Still... the supply at only 135*? on a furnaces designed for a 160* ...?

The temp rise on those beasts are between 80 and 100*.

Either the gas press is too low or your are wailing air thru the system or you temp tester is off.
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Old 03-06-2012, 09:46 AM   #39
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Proper ignition/blower sequence in older gas furnace?


Quote:
Still... the supply at only 135*? on a furnaces designed for a 160* ...?
Or are you saying that I should leave the cut in at 130 and that the burner should remain lit and capable of continuing to raise the plenum temp to 160, with the blower operating, then maintaining that 160 until the room thermostat is satisfied?

So...

1 thermostat tells burner it needs heat,
2 burner lights,
3 blower starts when furnace temp hits 130,
4 blower and burner work together while continuing a climb to approx 160 degrees,
5 when room thermostat is satisfied with the room temp the burner shuts off,
6 then the blower continues until the furnace temp is reduced to approx 90 to 100 degrees.

I should raise that "anticipator' setting then to keep the burner on longer yet and see if I can get the furnace temp higher during blower operation?
If that does not suffice then I need to investigate either why the burner is not hot enough or whether the CFM is in fact too high rather than, as I feared, too low.

********postscript****** just went down and went through the sequence again for the first time since I've had the motor running correctly.
The blower starts at 135 degrees. The temp drops within about one minute to 125 and then slowly rises to 145 degrees staying there. Burner shuts off and temp goes down and blower stops at about 95 degrees.

All in all, rather than having too little blower air as I originally suspected, I may have a tad too much. That would probably limit that droop to a few degrees initially and allow the operating temp to rise closer to 160.

Not sure if it's worth a new pulley and belt. Is it?

Last edited by frascati; 03-06-2012 at 10:52 AM.
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Old 03-06-2012, 11:35 AM   #40
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Proper ignition/blower sequence in older gas furnace?


In my temperate area, these furnaces are not uncommon.
If it's efficiency that you are after, the earlier the fan comes on and the
longer that it stays on after the burners shut off, the more you save.

My customers with lower operating temps on this style of furnace are getting longer lifespans and better efficiency from their exchangers.

My oldest units are using two speed motors that have a continuous air flow and lower fan settings and temps that provide surprisingly even home temps.

If you do want to increase the temp, then a steel split pulley will give you more speed flexibility. Hell, even a more restrictive air filter will do that but it would not be my advise to increase the operating temp of a 45 year + heat exchanger..

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