Heil NTGM 100 circulating blower runs all the time


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Old 01-06-12, 08:40 AM
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Heil NTGM 100 circulating blower runs all the time

Hello Everybody,

I found a thread from back in 2007 about a Heil furnace that prompted me to sign up. Someone named Pflor supplied some great info about this furnace.

Can anyone help me? The circulating blower in my Heil NTGM 100 never shuts off. I use the furnace in my workshop. From the moment the t'stat calls for heat, the blower runs. When the furnace is cool, I shut it off manually. The furnace cycles up OK, runs OK, and the gas shuts off OK, the blower just never shuts off. I've replaced the 1013104 (was 1010575) switch on the side of the burner box, and both P&B relays on the board. Any ideas? Thanks.
 
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Old 01-07-12, 05:55 PM
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Have you tried changing the timings for the fan as shown on the wiring diagram here? http://icpindexing.toddsit.com/docum...4003100301.pdf
 
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Old 01-09-12, 08:44 AM
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Fan timing

Hi Grady,

Thanks for the reply. By "fan timing" do you mean the little 3 position switch down in the lower left of the board? If so, yes. I just tried changing the settings (thinking that maybe the switch contacts were corroded) and nothing changed. When I turned on the main power to the furnace, the circulating blower started. This is a problem that just popped up. The furnace was OK when I shut it off at the end of the last heating season. When I turned it on this year, the circulating fan came on and won't shut off unless I turn off the main power to the furnace. How does the blower (if it's running correctly) know when to turn on and off? Is it strictly by time after the gas turns on and off? Or is there a sensor like in the old gas furnaces? Thanks for any help you can give me.

Al
 
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Old 01-09-12, 03:50 PM
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On most gas furnaces the fan operates strictly on a timer. The exception would be if there was a limit switch open but in that case the burners would not fire.

Something you can try is if there is a wire connected to the G terminal (where the thermostat wires connect to the furnace), disconnect it. If that cures the fan staying on problem, either there's a short in the t-stat wire or the stat itself is problematic.
 
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Old 01-11-12, 07:12 AM
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T'stat check

Hi Grady,

There's no wire on "G." I've got the t'stat hooked to "W" & "R." Just for the halibut (fish pun), I disconnected the t'stat and replaced it with a jumper. Everything was the same, so the t'stat is OK (it's a brand new heat only t'stat). The circulating blower and the exhaust blower both start up as soon as the power is turned on.

Al
 
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Old 01-11-12, 07:28 AM
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What do you mean by the "circulating blower"? I presume you mean the fan that circulates air around the house.

If so, there is a relay on the circuit board which is failing to open and shut off the fan reliably.

Replace the circuit board.
 
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Old 01-11-12, 04:33 PM
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I agree with S/P. You have a stuck relay on the board. Just had to rule out the wire/thermostat possibility.
 
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Old 01-12-12, 09:12 AM
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Circulating Blower and relay

Hello Grady and S/P,

Thanks for the help. I've already replaced the two big relays on the board (they're only about $3.15 each), but I discovered there's a little one, too. I'm gonna try replacing it too, before I spend big bucks on a board.

BTW, by "circulating blower" I do mean the one that blows warm air into the house.

It's probably gonna take a few days to get the relay, but I will definitely post another response to let you know how I make out.

Thanks again.

Al
 
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Old 01-27-12, 11:13 AM
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Hello Grady & Seattle Pioneer,

I promised to let you know how I made out, so here it is: I changed the other relay (K1) and that didn't fix it. But.....when I was changing it I noticed something I hadn't seen before. The pad which connects Z10 (a zener diode) to R39 (a resistor) looked as if it had gotten hot (the solder wasn't smooth). I checked Z10 and it looked bad, so I unsoldered it and took it off the board. When I took it off, part of the pad lifted off the board, so it had gotten hot. I checked the zener on the bench and it was bad (I used a ohmmeter and discovered that current flowed in both directions. Current should only flow from + to - , not in the opposite direction(+ is the end with no mark and - is the end with the black stripe). I found the diode (1N5231B) on eBay, put it in and it works!

K1 (Zettler AZ8-1CH-2$DE) cost me $.95, K2 & K3 (Potter & Brumfield T9AS5D12-24) cost $3.15 ea. and the 1N5231B cost $.23!

So I spent $7.25 on relays I didn't need ( I should have checked them out first) and ended up fixing the problem for $.23! Oh well, at least it's running. Thanks for your help. I hope somebody else can use the information, Too!

Al
 
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Old 01-27-12, 03:43 PM
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Al,

Thanks for the info on finding the cure. Sounds like you know your way around circuit boards. A diode allowing current flow in both directions would certainly cause your problem.
 
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Old 01-27-12, 09:33 PM
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Finding the problem

Hi grady,

I've been in the electronics business for 46 years, but only as a lowly tech. I can build the stuff, but I really don't know how it works (but I do keep my eyes and ears open, and I've picked up a few things along the way). Thank God I had that "hot spot" on the board to point out a good place to look for the problem. Otherwise I never would have found it.

Al
 
 

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