Armstrong furnace, Blower runs from the start

[bubinga1]

On a older Armstrong furnace, Its a Ultra II model EG6E, (circa 1990)
Were these systems designed/wired so as to have the blower come on right away with the t-Stat "call for heat"?, instead of relying on the limit control temp's on setting to power up the blower?
Looking at the schematic and studying it, and studying the relay's, it appears that the NC side of the fan relay (not energized in heat mode,energized with A/C only ) is getting power via the energized NO, STDP combustion relay, and cant help but power up the blower low speed with the initial start up of the furnace.
The limit control has been replaced.
Manual/Auto on limit control is set to auto.
Fan on/Auto on T-Stat is set to Auto.
Sorry I don't have a scanner to scan/E-mail the schematic.
I will try to get it scaned so I can post it.


Thank You, Anthony Diodati

[mdshunk]

I can't dig up a schematic on the Armstrong EG6E. I know it's a condensing gas furnace made about 1991. It has a Robertshaw ignition module, but that has nothing to do with the blower, as it is not one of the newer integrated ignition modules that also control the blower. One simple check you could go is see if you have 24VAC on the G terminal at the furnace (sould be a green wire). Check for 24 volts between G and the metal of the furnace, and see what you get. If you have 24 VAC here, then the stat is causing it to run. Thinking as I'm typing.... you said it only runs the blower on call for heat and not all the time.... better try to post a schematic.

[bubinga1]

Originally Posted by mdshunk

I can't dig up a schematic on the Armstrong EG6E. I know it's a condensing gas furnace made about 1991. It has a Robertshaw ignition module, but that has nothing to do with the blower, as it is not one of the newer integrated ignition modules that also control the blower. One simple check you could go is see if you have 24VAC on the G terminal at the furnace (sould be a green wire). Check for 24 volts between G and the metal of the furnace, and see what you get. If you have 24 VAC here, then the stat is causing it to run. Thinking as I'm typing.... you said it only runs the blower on call for heat and not all the time.... better try to post a schematic.

Yes, A schematic on the Armstrong EG6E would help.
Let me try to clear it up a little.
The blower fan runs at start up, or apon call for heat, IOW it does not let the burner come up to the fan limit control of ~120-130,and then come on. It (the blower) continues to run with the burner,then, when the t-Stat is "happy" with the room temp. the burner will shut ,the blower fan will continue to run till the fan limit reaches the 90 degree "fan off" temp, The fan limit control is set to as per the manual.
Here is a longer explation, Hope this makes sense. It is the best I can explaine it.

IOW is designed to operate the blower motor on low as soon as the t-stat calls for heat, instead of allowing the burner to burn for a few minuets before starting the blower.
All the looking at the schematic that I have done, and testing voltage at the relays and testing the relays for proper operation, according to the schematic, as far as NO/ NC/ and the opposite continuity/or lack of when the coil is energized. being confirmed, and again studying the schematic, leads me to believe this system is working as designed. I'll try to explain this the best I can.

It appears to me, + power comes in, (goes through the interlock)
to a 3 way connection; 1st to the power in side of the fan limit, 2nd to the 1st pole of the NO combustion blower relay,
a STDP relay (power is then bridged to the 2nd pole of the NO combustion blower relay, but that side is for the combustion blower) and then to the fan relay, (NO terminal (R2,S2 of the relay goes to the High of the blower motor, but that’s only used for the A/C, the fan relay is not energized in the heat mode.)

Now out of the Combustion blower relay, comes a red wire, and (when the t-stat calls for heat this NO relay is energized, and in now closed) sends power to the Red wire, that runs all the way up to the fan side of the limit control, and also taps off before limit control, to the NC side of the fan relay (R2, through the NC side, (witch is closed because the relay is not energized), out of there and to the low connection on the blower motor.
So IOW the power is fed out of the combustion relay, into the NC side of the fan relay, out of the NC side of the fan relay to the motor(low speed). After the burner shuts off the combustion blower relay drops the voltage to the NC side of the fan relay and the NC fan relay now gets its power from the Limit control.
See if I remove the red wire from the combustion relay, the blower does not run at the start of the cycle, but only comes on when the NC (side) of the fan relay gets power from the limit control.

The way I am reading the schematic, and have tested the relays , It seems to me the blower has no choice but to run at initial start-up.

Well I'm sure I made this "clear as mud" I wish I had a scanner to post the schematic, so You could see what the hell I'm talking about, If I am correct, or if I am missing something.
I may try to get someone to scan it and put it on a floppy so that I can post it.
I tried to find a schematic on line but had no luck.
Maybe the public libary in town has a scanner they will let me use.
Hope this makes sense.
Thanks, Tony D.

[Wgoodrich]

Limit relay is supposed to shut off the burner if gets too hot yet blower continues to run normally. Some limit controls shut all down.

I have tried to redraw what you are discribing but can not whip it.

In my personal feeling and by past experience I am suspecting a bad fan relay.

Watch the furnace and have someone turn it on by the Tstat. Watch the flame and see if it is licking out of the combustion chamber and liking up toward the fan switch. If this is happening then I suggest you clean your furnace burner vents being clogged and replace the fan switch.

I am suspecting you have a bad fan switch. Furnaces in this era you are talking normally have the blower over where you look in to see the flame. If the furnace needs cleaning flame will lick out the front of the burners and lick the fan switch.

Best suggestion I have is replace the fan switch.

May be wrong but not that expensive to prove me wrong then we can eliminate that fan switch being the culprit.

Suspect it is the culprit.

Let us know if this helps

Wg

[bubinga1]

See if this schematic helps any.

Unless I am missing something, this thing is wired to where the blower fan can "not help" but come on once the STDP NO Combustion blower relay is energized.

I have highlighted the "path" I suspect the voltage is taking.

Like I said, once the burner kicks off, the Blower fan is then receiving voltage from the fan limit control. Limit control then cools down to fan off temp of 90 degrees, and turns fan off as it should.

Hope this makes sense, and the schematic is large/clear enough to see.

Fan limit control is new last week
You May have to save it,and open picture view to enlarge it.
Thanks, Tony D.
**EDIT***This is Small, I am going to try it as an attachment as well.
I can also E mail the attachment if needed, please provide E mail address.
ThanksTony D.

[mdshunk]

I'm sorry to say that I can't make out a thing on the wiring diagram. It's just too small. I'm going to get the full sized wiring diagram from Armstrong (really it's a Lennox sister line) on Monday. It costs 35 bucks to get info faxed on weekends from Lennox, so I'll get it this .... WAIT .... Monday is some sort of holiday, Tuesday I'll get it. It's free during regular business hours.

[bubinga1]

Originally Posted by mdshunk

I'm sorry to say that I can't make out a thing on the wiring diagram. It's just too small. I'm going to get the full sized wiring diagram from Armstrong (really it's a Lennox sister line) on Monday. It costs 35 bucks to get info faxed on weekends from Lennox, so I'll get it this .... WAIT .... Monday is some sort of holiday, Tuesday I'll get it. It's free during regular business hours.

Hey Great thanks a lot.
Even if I e mailed it it probley won't be much better.
I had the liabary scan it to a floppy, but she said the next size up would'nt fit on a floppy.
I dont have a digitial camera either or I might be able to take a picture of the one on the blower door.
I can read that one OK, in picture view, if I zoom in on it 2X but then again, I'm used to looking at my copy.
Thanks for the help.
Tony

[bubinga1]

See If this one is a little better.
I have highlighted in red the path I supect the voltage is taking at start-up.

I did not highlight the second path, but you can see, after the burner shuts off, the combustion blower relay is no longer energized, and the blower then recives voltage through the Fan limit control.
Thanks for looking, Tony D.

[mdshunk]

Yep... It appears like the furnace is factory wired to bring the blower on at the instant the thermostat calls for heat. The furnace heats up, closing the fan switch so that the fan switch holds the blower on after a call for heat ends until the fan switch is cooled back down. Kinda different. There's one connection you could change in the junction box to modify this, but I'm still thinking why they did it this way. There's two events that will turn on the blower... call for heat and fan switch making on heat exchanger temperature rise. Normally, heat exchanger temperature rise is the only event that will turn the blower on. Some of the real new furnaces will turn on the blower permanently to alert the homeowner of trouble, but this is not the case with your furnace.

There is a wire on terminal 1 of R1. The other end of this wire goes to a wire nut junction box connection, and then directly to the normally closed contact in the transformer/relay center. If this wire, instead of going to the wire nut connection, went to the other side of the fan switch, the unit would operate "conventionally". I know this will work, but I'm still struggling to think of what the implications would be. There must be a reason that it is factory wired this way. Perhaps that it is a "fail safe", self preservation strategy for an otherwise flimsy heat exchanger? (many furnace heat exchangers nowadays are crimped instead of welded... not my first choice how I'd build a furnace. Dishonest technicians can do things while servicing your furnace to literally "pop" your heat exchanger in an effort to sell you a new furnace.)

I think the short answer is... your furnace ain't broke. No repair required.

[Wgoodrich]

Guys, look at the schematic again. Look at the hot and grounded leg [aka neutral] feeding that furnace.

Think that the dotted line is the grounded leg not the hot. Think that the black line goes to the high limit then to the thermostat.

Key point on this schematic is that switching and safety circuit are wire on both the hot and the grounded leg [aka neutral].

If you look close you are seeing red tracer is tracing the neutral wire not the hot wire. Takes both to operate. Track with a green marker or other obvious marker the electrical path of that hot wire feeding into the furnace. You should find until the fan switch closes the fan will not start.

You should also notice that the dotted line [grounded leg / aka neutral] is where the door switches [aka safety circuit] and other controllers are controled [switched] by the dotted line [grounded leg / aka neutral side]

Contorl switching on this furnace uses both the hot and the white wires [aka neutral / grounded leg]. This is approved by teh NEC for motor control wiring using the neutral in the switching of control wiring.

Suspect this is what is throwing you off.

I picked up that you have changed the fan switch. Is this true? If so check to see if your high limit has tripped out.

Wg