Power Vent Induction FanMotor can be HOT-WIRED to start, but wont start normally

I'm new here and looking for help.

My problem is with a Goodman-Janitrol series "GMP" gas furnace not working, and of course it is like 5 degrees out now - the coldest day of the year so far here in Michigan.

Someone, I think, messed it up (the tenant) and now I'm trying to fix it.

I think the cause of the problem is that the power vent induction motor will not start running (thus the rest of the ignition cylce does not occur).

I took the power vent induction motor leads off the motor, and HOT-WIRED it to test it (I ran wires from an AC outlet directly to the motor leads, and it turns on and runs strong). I also OHM'd the leads on the motor, and did get an OHM reading there.

With the motor HOT-WIRED, the rest of the furnace starts (the igniter and main burners come on) - at least for a minute or so. Then a red LED flashes twice, which the panel diagram says is that the "vent pressure switch is closed" - and the furnace shuts down. I may have a bad pressure switch, but keep in mind I had to HOT-WIRE the vent induction fan motor to even get this far.

My first question is why won't the vent induction fan motor start NORMALLY? I have checked that the fuse on the circuit board is good, and also checked the voltage going to the vent fan motor - and there was no voltage there! Is this no voltage to the vent blower fan due to a bad circuit board?

The thermostat was working, and I even took the thermostat off the wall and I twisted the two thermostat wires together to make those wires demand the furnace on. (I did check that the thermostat wires had voltage, and they had about 20 volts at the thermostat before I twisted the wires together - just to be sure).

I did have to "fix" the power vent motor, as "someone" had broken one of the leads off it. I clamped on a new lead to a thin wire that was near where the lead should have been, and that seems to have gotten the motor able to run when it is HOT-WIRED (as I said above).

My second question has to do with the 2 wires coming off the CAPACITOR. For some reason, one of the wires is just hanging there inside the furnace box, and the other goes to a lead on the circuit board. This hanging wire does not seem correct, but where should it go - and does it have anything to do with the power vent fan induction motor not getting any voltage normally?

What could I check next? (I can follow directions, and could really use some good direction right now!

My third question is, if the thermostat is set to the ON position, instead of AUTO, shouldn't the main blower fan kick on immediately, even of the vent blower motor does not?

My fourth question is, my manual says that this furnace has an integrated Hot Surface Igniter/Fan Control. Does this mean it controls the vent fan, or the main blower fan? If the Igniter/Fan control affects the vent motor - then could that igniter be getting weak, and not causing voltage to not be sent to the vent motor?

Thanks in advance for any help!

PS: This all started when the tenant called, saying the furnace was not on, and he thought the vent motor was broken. (I think he broke the lead off the vent motor!) I really thought I was home free after I replaced the lead on the vent motor, and bench tested it by HOT-WIRING it and seeing it run, , (and after I removed the dead bird from it - which I thought at the time was the entire problem as to why it stopped spinning - which it would not do since there was a dead bird stuck in the vent motor fan blades). But as described above, I am now not getting power normally to the vent motor. (Sorry, I just had to vent a little about the tenant )

 

Well, today i tried a new approach to see why the inducer motor will not start on its own.

I thought I'd eliminate the thermostat as a culprit, so I removed the Red and White t-stat wires from the board and placed a jumper wire across the 2 terminals. Still no inducer start.

I then measured the AC voltage at the board, for the 2 wires going to the inducer motor. No voltage there. I did this both with the inducer motor wires attached, and unattached, from the circuit board.

I then added a new pressure switch, as my manual said that if it is bad, it prevents the furnace from operating (and the next step in the operation is to energize the inducer fan - which is what I'm not getting - so I added the new pressure switch).

The only other thing my manual said is the limit switches are tested as part of start up, and if they are open, then the ignition won't start - but that the inducer will still be "energized". (Since I get no voltage to the inducer, I can't see where the limits are the problem).

I am almost sure the circuit board is bad at this point.

I went to look at replacement boards, and they look a bit different than what I have in my furnace.

I currently have a circuit board with part number of B18099-06, and that is no longer made. The replacement is part number is a board type: B18099-13. (The manufacturers part number is 50T35-743).

So now I am reading the installation instructions for the new circuit board (I had the part dealer make me a copy) and may go out in the morning and buy it.

Anyone here think the problem with the inducer not starting "normally" is something other than the circuit board? (The inducer can be jump started via direct electric current from a second AC outlet).

The board did show power, as the red LED was on.

The only thing I'm a little unclear of is when I put a meter on the leads coming from the bottom of the transformer that were marked "COM" and "120V" respectivey, I read a voltage of about 24 volts. I thought this is correct, because I thought what the transformer does is input 120v from the house current, and put out 24v to the circuit board. (But then why is one of the two leads labeled 120v?) The 2 black and white wires from these transformer pins go to 2 leads on the circuit board labeled "PRT TRANS"

The other side (the top of the transformer) has 3 leads and 3 wires coming off it. These go to a ground on the board, a pin called "24 VAC" on the board, and a pin called "COM" on the board. (I never bothered measuring the voltage there - maybe I should have).

Do I have a good transformer?

 

Measure voltage between 24 VAC & Com. Some of these boards have a fuse. If I remember correctly, the -6 does not but the -13 does. Board problems are quite common with the 6 series boards. Screwy blink codes are often a symptom of a bad board. One of the most common is a '2' & when you check the pressure switch, it is open not closed as the board would have you believe.

 

I'd imagine what is marked 24 volts should be 24 volts. How come you did all that other testing and then said all you did, but then did not go back to test the outgoing side of the transformer that goes to the 24 volts on the board? Just curious.

 

ecman,

good question. I thought I was testing the low voltage side of the transformer when I tested it earlier today. Later tonight as I was looking at the schematic for the circuit board is when I realized the "bottom" of the transformer was probably the input (120v) side - and not the the output (24v) side - as I assumed earlier when I did the test.

Also, I thought I had already diagnosed the problem as a bad board, since I was getting no voltage to the vent motor with the jumper on the thermostat leads - and - I could hot wire the vent motor to run and the furnace fired up - so that earlier voltage test was a "curisoity" test - and I guess I did not pay attention to what I was "testing". My memory is even failing me now, and I'm not even sure if I had the voltage meter on the 50 or 250 setting when I did that test. I think I just tried too many things today, and learning all about this as I go has a way to get my brain thinking incorrectly sometimes

 

grady, you mean on the output side of the transformer?

Also, I did measure voltage more carefully on the thermostat wires, and did see 24v there, so as I think about it I must have 24v going to the board from the transformer.

But I think I did mess up that earlier voltage reading on the transformer.

Part of the problem is I have on older mulitmeter, and there are a lot of dial settings. I am also learning how to do electrical test, and learning about furnace electronics, all at the same time. (My multimeter dial has settings for AC volts (with settings of 10, 50, 250, and 1000) OHMS (RX1, RX10, RX1k), DC voltage(5, 25, 125, and 500), and DC amps (250m, 50u) - and then I need to read the several bands on the needle after I get the dial set right, and the correct test on the correct electronics, and well, sometimes I think I get it wrong, cause I'm learning as I go

 

When you get a new board, it will be a 13 series. The wiring is not the same but there are instructions & wires with the new board. Read & follow the instructions carefully.

I suggest you go to Radio Shack or other electronics store & get some resistors to play with while teaching yourself to use your meter. I have a couple of auto ranging digital meters but often go back to my old analog.

 

Grady, Good advice. Best to fully understand it before trying to debug/understand faults with it.

So, I bought a new circuit board and installed it today. When All said and done, it went pretty well. Took me an hour or so, cause I was being real careful. With the new board, my vent blower fan finally came on.

I looked at the old board, and there was what looked like a black burned spot on the back of it, almost as if a flame had been held to the board. The area was a little bigger than the size of a quarter, and right behind the lead on the board labeled "IND" - which I think is for the Induction Blower (vent fan). I wish I had know to look for such evidence earlier, I could have pulled the circuit board off and seen this evidence of a failed board, and got myself to the point of buying the new board a lot sooner.

Then another problem happened. I got to the point that the HSI (Hot surface ignitor) glowed, but the mian burners did not fire up. After 4 attempts I saw the furnace LED light flashing 'ignition failure (with listed possible reasons of: Gas flow, or Gas pressure, or Gas valve, or flame sensor). The first 3 did not make much sense, as the furnace was firing up ok before all these recent problems.

I though it might well be the flame sensor rod, but since I did not smell any unburned natural gas (as I thought I should if the main had opened) and decided to test the voltage at the gas valve. I hooked the multimeter to 1 lead on gas valve and the other lead to ground, and got no voltage at the gas valve. I was at least relieved it was not gas valve that just went out, but had to find out why no voltage.

I called a parts place, and got a helpful guty there who told me to test the Limit Switch, and the Flame RollOut switches. Sure enough, one of the flame rollout switches was not sending 24v to the gas valve. (I tested the falme rollout switch by putting 1 test lead from the mulitmeter on the flame rollout switch lead, and the other to ground). He then told me there is a manual reset button on the flame rollout switch. I pushed it in, and retested, and now got voltage out of the switch, and to the gas valve. (I found there are 4 flame rollout switches on my Goodman furnace. 3 are in the upper part of the cabinet, on a steel housing that surrounds the 3 flame venturis. One on top, and the other 2 on each side of the steel box. The 4th is in the lower part of the furnace cabinet, where the circuit board is. They are so small I never even noticed them. The switch itself is not more then twice the size of the electric leads on them).

So now I started the furnace again, and the flame came on, but only burned for about 5 seconds, and then wnet out. I made progress, but still short of the goal. I then thought about that flame sensor rod, and pulled it out, and cleaned it up with steel wool. It did not look terribly dirty, just a bit tarnished, but I made it more shiny with the steel wool, and after reinstalling it, the furnace started working normally.

It went through several start up/shut down cycles normally, but did mess up once. Same thing, main burner falmes came on for about 3-5 seconds and shut down, and again the LED was blinking 'Ignition Failure'. I checked the reset buttons on the 3 flame rollout switches, and 1 had popped up again. After pushing the reset button down, the furnace started normally again.

I was reading the forums here, and someone posted that the flame rollout switch is supposed to make sure the ignition flames are not blowing back from the venturis, and that other possible causes for flame rollout switch opening are:
1 - reverse draft down chimney
2 - blocked chimney or flue
3 - lack of combustible air
4 - defective flame roll out switch

Now I am thinking I may have an obstruction in the flue venting to the chimney, or in the chimney. (I already pulled 1 dead bird from the squirrel cage that is in the vent blower fan, and could have another somewhere in the chimney). So I plan to inspect the steel flue going to the chimney, and maybe get some new flame roll out switches.

What do you think? ANy other reasons for flame roll out switches opening up?

PS: (I also think I need to matbe hire someone to climb up on the roof of this 2 story house, and make sure some type of screen or cap is on top of the chimney that will keep the birds out!)

Also, I thought the voltage to the induction vent fan is supposed to be 120v? I don't think I caused the circuit board problem\burn, when I applied direct AC voltage to the induction vent fan in order to jump start it - as that vent fan was not getting voltage to it before all my efforts to HOT-WIRE jump start it. I am still trying to figure out what happened to that induction vent fan. (Someone broke one of the leads off it). But I don't think that would leave evidence of the burning on the back of the furnace circuit board?

 

I would say check the flue and make sure it's clear. Then I would replace the roll-out switch just to rule that out.

I believe some of the older gmp furnaces had a clam shell heat exchanger that is held together with crimp rings. If these rings fail, the heat exchanger could leak, possibly causing a roll-out condition. The rings (if failed) will drop straight down below the heat exchanger. Look for them. In a horizontal install, you may have to remove the blower assembly.

 

JimConnor,

I agree, will check the flue and get a new flame roll out switch.

I'll have to look to see if I can find the "clam shell heat exchanger that is held together with crimp rings". I was not looking at that part of the furnace, and I'm not really sure what it looks like. Would that be above, or below the main burners?

Have you ever removed the main blower assembly/motor?

I was looking at the cabinet, and I assume that to get to the main blower motor - I would have to remove the intake ductwork which attaches, in my case, to an electric air cleaner cabinet, in order to get to the opening in the furnace cabinet (where the air filter is) - in order to access the blower motor? Is this a difficult job?

 

The gmp can be positioned horizontally or vertically. I assume yours is positioned vertically and the air flows upward. The front has two access panels. The blower is behind the lower (more than likely you saw it when you replaced the board). The blower assembly is held in place by bolts (don't remember how many), but should be removable through the front. The heat exchanger is immediately above the blower in the upper half of the furnace.

 

Jim-connor,

Thanks for that info. Yes, mine is horizontally installed. So you are saying that to get to the blower, I would have to pull out the circuit board and wires?

These crimp rings, if they fail, the only way to know is to pull the motor and look?

I started to try and and take some pieces of the flue apart today to inspect them, but I could only get a couple of the sheet metal screws to actually extract out of the sheet metal. The majority of them just rotated in their holes, but never backed out of the holes. Is their a trick to get them out? I even tried using pliers and pulling out on the screws as I turned them, but the piers kept slipping off the screw heads! I tried using a second screw driver and forcing it under the heads of the sheet metal screws to pry them out as I turned the screws with a 2nd screwdriver....

 

Unfortunately, yes.

Possibly. I don't know your setup. You may be able to look at things on the supply side (air discharge side of furnace), depending on your ducting, evap coil, and transition (if used).

I would say a visual inspection is one of the best ways to detect a leaking heat exchanger. But there are also several other methods.

Flue pipe can be a lot of fun to disassemble, and even more fun to get it back together. Older flue pipe usually has some degree of corrosion which creates some friction. New flue pipe is smooth, bright, and has oil on it from the factory.

 

Jim, Well it ran good for 2 days now, but the main burners failed to come on, the hot surface ignitor glowed, and I found 1 of the 4 flame roll out switches had "popped" out again. That is a different one than was tripped the first time. (The 1st one was in the top cabinet, the 2nd one was in the bottom cabinet of the furnace - there's actually 4 in there).

I'm really thinking there might be blockage in the flue. I mentioned that I had found a dead bird in the vent fan motor when I took it off a week ago, and yesterday I heard another bird fluttering around in somewhere, might have been in the flue, or in the chimney (or one of the other 3 flues as this house has 2 furnaces and 2 hot water heaters, for a total of 4 flues). That's why I wanted to get the vent pipes off and look inside, to see if a brid was in the flue leading to the malfunctioning furnace. So I'm going to try again to get the vent pipes apart, and see if there is a dead bird in there. (Sounds quicker and more likely now to look for a bird in there as a starting point).

Got any tips for getting those pesky screws out?

Also, wondering how I can check the chimney. I did notice a trap door in the bottom of the chimney, but that is below the level of where the flue pipes enter the chimney, so I'm not sure what I could accomplish by opening that trap door?

 

That trap door is probably a chimney cleanout. I'd check there before taking the flue apart. Screws may come out with pliers.

 

I took the vent induction motor off, and found more remains from a dead bird in it. I believe that was what was causing the flame roll out switch to trip.

I also took the flue vent going to the chimney apart, and got a small amount of sand out of it. (BTW, I managed to get those pesky sheet metal screws out by putting the tip of a small steak knife under the lip of the screw while turning it, and gradually working more of the knife under the head while keeping outward pressure on the srew head from underneath it - and after I had squirted a small amount of penetrating oil on them.)

I did not notice any real flames blowing back and out of the furnace. The flame was mostly blue, and mostly firing into the 3 heat exchanger opemings, like a jet.

I did notice that the sheet metal frame that the flame roll out switches and gas valve are mounted on got fairly hot. Especially in the middle, not so much on the ends of the metal frame. I cold put my finger on the sheet metal for only a couple of seconds before it felt like it was starting to get too hot for my finger. Is this normal? The metal enclosing the vent induction motor was real hot, but since that mounts (at least it looks like) right up against front of the heat exchanger - I assume that is normal?

I think I need someone to come out and climb up on the roof of this 2 story house, and put some kind of wire cage or something up there to keep the birds out. This is the 2nd bird I've found in the induction vent blower in the last week and a half. Anyone have any ideas to keep the birds from blocking up my vent motor? Could I put some kinf of screening in the vent ducting between the furnace on where the ducting goes into the chimney?

Know anyone in Detroit area that can climb up on the roof?

 

My flame roll out switches, on a goodman GMP furnace, appear to being tripped occassionaly, I beleive due to the metal housing that the flame roll out switches and gas valve are mounted on - getting too hot. (I see no evidence of flame roll out as I watch the flames, and there is no burning of wiring, or other charring or black spots in the furnace cabinet).

I put my finger on the sheet metal for only a couple of seconds, before it felt like it was starting to burn my finger. Is this normal?

Could this heat transfer in the housing the sensors are mounted on (as opposed to direct flame) cause the roll out switch to trip? If so, could this be due to dirty flame housing, or something else, causing too much heat transfer from the heat exchange, or blower orifices?

I felt the heat buildup on the metal housing on a newer, 5 year old amana furnace, and the sheet metal that the roll out switches, and burners mount to, did not feel as hot.