RobertShaw SP735A Follow up.

[Anthony Diodati]

Don't know if you can help me with this issue, but here goes. The Unit is a Armstrong Ultra II . The maintenance Instructions cover model series EG6E And EG7E. This is the EG6E,according to the model #. Ok, Last week, Girlfriend wakes me up, Cold in house, said burner was not lit.) We had replaced Combustion blower last winter, system worked OK after that.)

I went down and opened furnace, Combustion blower was running, checked pressure switch with ohm meter, switch was closed. Pilot not lighting.

This is 10:00 at night, did not know what else to do. (Used to work as auto mechanic, sometimes taping a component would get car to start, or motor to falter, depending on suspect component.

Anyways, tap on board,(RobertShaw SP735A)lightly with stick. Tic-Tic-Tic-Tic-Tic-Tic- goes the igniter, pilot is lit, click-click-click goes the gas valve, burner lights, have heat rest of night. Next day SOS. Order new robertshaw SP735A, while I'm at it the other thing this furnace always did, was as soon as the T-Stat call's for heat the blower-fan always started right away. Furnace would cycle,(normal length of time) shut off, 10 seconds or so later fan kicks back on for about 1 minuet, shuts off till next heating cycle.

Suspect limit control, remove cover, find wire on left side burnt about 1/4" from switch, remove limit control, fix wire, same old story.

remove limit control again, open switch find contact points on that side(left as looking at it)burnt, find points staying open, switch arm not moving.

OK bad limit control.

Replace board and limit control, burners lighting all the time OK, fan still coming on from "get go"(manual/auto, on new limit control set to auto, Auto/fan on, set to Auto at t-stat also)

I left the hi-low voltage break-away tab in place, as that's the way the old one was.

Three wires total on this limit control, blue upper left, red upper right, black bottom.

Furnace (burner and fan) will run for a while, burner will kick off, (blower still running)

"Seems" to kick off(burner) at point when limit control should turn fan on.(I have it set to 120)

Waite a while watching limit control, almost to fan off point, burner will kick back on.

Looking at wiring diagram that came with new limit control upper left is fan control.

If I turn off furnace, disconnect blue wire, turn furnace back on; fan still starts from get go. There is 120Volt at disconnected blue wire with furnace running.

I wonder if its possible that the blue, (upper left) and red,(upper right may be reversed it the junction box?

Or other wise wired wrong? Or possible bad relay?

Furnace is warming house, thermometer in T-Stat even with set point, but this system is running almost constantly. Will shut off, (fan and blower) then less than a minuet later back on. Seems this system is running WAY TOO MUCH.

It is cold ~ 15 degrees, but this still seems like system is running too much.

Any thoughts, (Other than calling a repair tech) appreciated.

SWMBO say's it's coming on,and heating the house,so it's OK, and does not want to put any more money into it.

Anthony Diodati

[Anthony Diodati]

Got it. Manual called for a anticipator setting of .9 ; This one was only set to .3 Set it to .9 furnace is cycling perfect now. Burner is staying on for full cycle,burner shuts off, blower fan continues to run till limit control reaches off point of 90 degrees(as per manual.), then blower turns off. blower fan is still starting upon call for heat, but I guess I can live with it for now. Guess I lucked out. Thanks, Tony D.

[TURTLE]

This is Turtle.

If you want to fix the fan coming on when you call for heat. Read the instruction for installing the fan / limit switch and set the tempersture settings where they are suppose to be to stop this problem.

TURTLE

[Anthony Diodati]

Thanks Turtle,

Yes I'd love to fix the fan coming on from get go,But here's the thing. I do have the on temp set to ~120,But the fan seems to be receiving power from somewhere else. Looking at wiring diagram that came with new limit control upper left is fan control.(Blue Wire)

If I turn off furnace, disconnect blue wire, turn furnace back on; fan still starts from get go. There is 120Volts already, at disconnected blue wire with furnace running. And there is NO voltage at fan side of limit control(wire still disconnected) UNTIL limit control reaches ~120.Then the fan side of the limit control receives power from the Black wire/terminal.

Then I wondered if it was possible that the blue, (upper left) and red,(upper right may be reversed it the junction box? But no, according to the schematic and the color codes they are wired correct in the junction box. I do see on the schematic that there is a relay(after the limit control) ,R2(red wire in)/S1(red wire out, to low of blower motor.) These two contacts,(R2/S1) are closed full time until 26 volts is applied to the windings of the relay,("G"/"C") but there is no voltage at the windings with the furnace in operation, only if the A/C is turned on, so I "assume" this in normal.

Also thinking that since the blue wire was burnt on the old limit control near where it pushes into the limit control, Possibly had shorted to another wire elsewhere like in the junction box or near the blower motor, but these all appear to be OK. Thanks, Tony D.

[CBhvac]

Much poking and prodding and parts changing snipped.

Define too much if you dont know the design temp of the unit.

Yea...but you wont like it.

Then short of putting in a new fan control relay, or calling someone in that can prob fix it for less than its going to cost running all the time....well..dont.

[Anthony Diodati]

Well you know cb, The fact is ,maybe you should re-read my OP of this thread. The fact of the matter is, the system is NOT running all the time anymore. Bumping up the anticipator from .3 to .9 as per the manual took care of that. The fact remains the board WAS bad, as it is always lighting now and IFAIK the ground was good, because I even carefully ran a new ground wire to the old board. (thank you for that"bad ground" tip BTY) The limit control WAS bad, because when I opened the switch(limit control) as I stated in the OP, the points were burnt, and the arm that the "cam, or off-sets" move to open the contacts was stuck. (contact points open) It was like I said last year to your "yellow pages" reply."After bench testing the combustion blower, and proving voltage to the combustion blower, I determined that the combustion blower was bad, and needed replaced 1st. and then go from there." Same in the case of the limit control and the board.

As far as the fan relay, I don't think I want to "throw that part at it" yet, because according to the schematic, and my bench test of both relays, ( 24 volt A/C power supply,Ohm meter)they seem to be working as they should. I believe,according to the schematic,(not certain now) the relay on top, marked R1 on the schematic) is the combustion blower relay, And the relay that plugs into the junction box/transformer is the fan relay.(?) If you care to be so kind, may I ask is this relay supposed to be energized all the time,(furnace on of course) or just with the A/C? ,(Hi blower) As this is the only time the relay coil is energized.(with the A/C)The relay coils are wired to "G"&"C" of the transformer. However,I noticed if I remove the black wire ,marked # 3 from the (combustion relay?),relay R1, at furnace start up, the blower will shut off, and then will not kick back on till the limit control reaches the on temp setting.

The schematic show's black wire ,power in to terminal #3, then off of terminal 3, "bridges" over to terminal # 6. # 3 sends power to # 1 when the relay is closed.

So actually, that's the only problem we are having at this time, (Unless I create more :>) I.E. the blower is starting from "get go" Now as far as the fan off, that seems OK, as after the burner shuts off, the blower runs till the limit control reaches it's "off" set point of 90 degrees.

You already know I don't know what I doing 100% or maybe not even 20%, but I am learning some things. What if Thomas Edison had been told to "quit f***ing around" ,and he listened. We both might not have jobs today. LOL. BTY how long did you *1st* have to go to school to learn this? Of course I know fresh out of school, there is still a lot to learn, but just the initial schooling? As I may have the chance to go back to school. I know, I need to Right? Serious question above though. Thanks, for reading.Tony D.

[CBhvac]

First...dont take matter of fact statements as being smartassed, altho, its obvious you did. Its ok...not here to win friends, or worry about enemies, just try to be matter of fact in the dealings with equipment..thats all. There are times, when it looks like your best, and cheapest fix WOULD be a tech, and thus, the Yellow Pages reply at times. Most guys in the trade will not even bother with this group and as most know in here, the other group is very non helpful 90% of the time, as it was originally intended. There was no offense intended, altho, it may at times appear that way...

Now that thats been enshrined in Google forever, or until the database crashes and cant be recovered, back on point about your relay.. See below.

Yup...should be...probably a Honeywell R82000 series, or a steveco 90-300 something series...might be a steveco 902** series as well...depends...if its a SPDT, SPNO, or a SPNO coil. More than likely, its a stevco 90-380, and thats a SPNO-SPNC coil..

Well...since on that furnace, the fan limit switch controls the fan when in heat mode, unless the fan switch is shorted, then the relay does indeed control the fan in AC mode, unless its shorted...or stuck. Depending on the configuration of the relay, there should be 24VAC on ONE side of the coil, possible that its on both sides if the unit uses another switch, like the thermostat to close the circuit to close the relay, and if its only got 4 terminals on it, it should have 110-115 only on one side of the relay in heat mode. G is your fan control from stat. C is your common to the system, meaning, the OTHER wire on the secondary 24VAC output side of the transformer

Ok...got a picture in my head...and it says.....relay stuck...but have you checked across the load side to see if its closed or open? Sure sounds closed to me..

Understood.

Depends on what you call school...formal college? LOL..please...I was bored out of my freaking skull there...

1 month, and I quit. Thats the tech end of it. A fella out in CA took me under his wing, and I got my 4 years apprenticeship, and was running calls solo with a zero callback ratio in less than 6 months. He still tells people to this day he let me leave because I was making him look bad..LOL.. Seriously...I dont know why, but I have never had a problem with tech items. I dont know if it was the time in Germany with MBB aircraft, or what, but show me a diagram, get out of the way, and its right in moments....no..I am NOT perfect. Far from it. I have made a few mistakes on the way, and I would be a liar if I said otherwise. Its just that there are times, particularly when the liability is so high, that short, and non sugar coated answers are best, and when you see professionals screw up and get killed or burned to a crisp in front of you a time or two....its hard to start handing out advice at times...no matter how long ago it was.

Good...seriously....just make sure its the trade, or profession you want and enjoy..

Never said that...Turtle says it best...Every day is like my first day on the job...and if its not, then you are NOT learning..

[Anthony Diodati]

Thanks CBhvac. Sometimes e mails and posts can have a way of coming off as they weren't intended. I think my last reply may have too. I took the heat a little the 1st time, but I was cool with it this time. I was actually sort of laughing when I was typing the last response. It's a lot different if your talking to someone in person. And I understand your point about the danger of fooling around with something your not experienced with. I am certain that system has potential to do great personal injury and property damage.

But it wasn't like I was in there just changing any and every thing I saw.( gee, wonder if I change the Gas valve next,that will fix the fan? ;>8), I had a *basic* understanding of how this thing was supposed to work, and last week when the system would not light,and the combustion blower was running, and the pressure switch was closed, it was sort of a "last ditch" effort to tap on the board. Lucky for me it worked, cause I'm sure it could have been many other things. So then I did a little more reading, and learned about the limit control, and went from there. I'll have to study your reply a little more, and maybe recheck the relay with that in mind. I see what you mean about guys in the trade not bothering, that's why I did not post at alt.HVAC, it seems that's more of a group for the trade guys to shoot the breeze.

You were lucky you got someone to "take you under there wing" and get into a good trade. I was too much of a young dumb ass when I was young, to listen to anyone and get into one of the trade unions. So now I am still trying to get into a decent paying field. None of the Electrical or HVAC company's in the area seem to want to hire a helper/apprentice. (Wheeling WV) It's bad around here, I might move back to the Pittsburgh area.

So I'll look at the system a little more with the above in mind. Thanks, Again, Tony D.

[Anthony Diodati]

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. You May have to save it,and open picture view to enlarge it.

Fan limit control is new last week

Got a lead/Phone # of the local #33, going to call him monday to see about the apprenticship program. Thanks, Tony D.

[Anthony Diodati]