Hello all!
I am having problems with my gas forced air furnace...
Model Number C9MPD100J14B1


Here is my problem... The furnace will start up and run for the whole cycle or just a minute or two... then shuts down and will not restart again until I open the front panel... turn it off... and go through the whole routine once again and now it has stopped even doing that...I am trying to solve the problem without the help of the furnace repair guy.

I know it is not the thermostat as I have just replaced it with a NEST and pulled brand new thermostat wiring. Also, to confirm... when disconnected from the thermostat, it would do the same thing with the jumper cable (not sure if that is the correct term).

The main gas valve is blinking a steady dim/bright sequence...
I guess what I am trying to figure what parts I need... whether it is the control board or the main gas valve.

I am just a regular home owner that is not afraid to get my hands dirty...

 

Do you have a flash code present on your control board?

 

I do. It is similar to the one above... it has a heartbeat!

 

Here is a link to some information that may be useful to you:

http://www.havenhomeclimatecare.ca/w...rite-c9mpd.pdf

If you remove the access panel or shut the breaker off and back on you will lost the flash code(s). As the attachment states in my previous post you can recall the last stored code by removing one of the wires from the main or rollout switch.

When you installed the Nest thermostat did you connect a wire to the C terminal to provide constant voltage to it? If you did not, that could be the root cause of your issue.

 

Here is the diagnostic code... I have a steady flash...
Is this for the control board or the gas valve?

 

I did add a c terminal. I have the W1, G, Rh, C wires attached... did that diagnostic with the NEST people (complete rewire). The furnace guy came out yesterday, i don't really trust that he knows exactly what he is doing. He did remove the thermostat from the control board and attached a red and white jumper wire to see if it would run without the thermostat attached. It did until he disconnected and reconnected the jumper wire. Which was the whole reason I bought a new thermostat...(I originally thought it was a bad thermostat...)

 

The flash code is for the control board. Did you measure for 24V between R and C terminals on the thermostat?

Are you saying you had the same issue with the furnace before replacing the thermostat?

 

yes.
and yes... I did have the same problem.
Sorry I jumped in my earlier post... lol. Been a long, chilly weekend trying to solve this problem. I originally bought a new thermostat because the system was starting and then shutting down. I figured it was in part because the thermostat was bad and the wiring was old. I replaced the thermostat wire and the new thermostat... all working properly.

the system however will start after a reset (until today), run a cycle, and then not start up again with or without the thermostat connected.

 

I suggest when you call for heat and the inducer motor starts spinning watch the flash code to see if it changes from the heartbeat.

Do you have one or two pressure switches?

 

It did not change yesterday... today it won't even fire up... but the steady heartbeat is still the same.... Im not sure as to how many pressure switches...


and thank you soooo much for trying to help!

 

I see one pressure switch in the photo you posted. I circled it in white on your photo. When your furnace is running and shuts down the control board should show 6 flashes or another code such as a pressure switch has opened (3 flashes). A couple of things I would do is:

Remove the flame rod and clean it with steel wool or light sandpaper and then wipe with a paper towel.

Remove the hose from the pressure switch attaches to the inducer motor. The inducer motor has a port on it where that hose attaches. That port can build up crud and needs to be cleaned on a regular basis. You can use a small drill bit or opened paper clip to ream it out ensuring it is clear all the way through. Also remove the hose and make sure is clear all the way through.

Also make sure the condensate drain system is draining freely through the trap and hoses.

 

Ok! I will give those suggestions a try and let ya know what happens!

 

When you clean the flame rod use extreme caution as the ignitor right next to it is very brittle. Do not touch the ignitor with your fingers. The attached image shows what the flame rod will look like. It is the steel rod with the bend on the right that needs to be cleaned. Over time deposits coat the rod and prevent the required amount of voltage to provide feedback to the control board.

 

thanks! took me a minute to find it... cleaned it carefully and did not touch the ignitor... problem is I turned off the gas and it did not ignite that go around... now it is doing it's "I don't want to rev up again" thing. I really think this thing is possessed.

 

Are you saying the inducer motor is not starting?

 

its sporadic. it will start for the first go around... and then not a second time

 

I suggest you inspect the terminals where the leads from the inducer motor connect to the control board. There should be a black wire that attaches to a two-pin connector on the board and a white wire that goes to the bank of neutral connectors, Remove those two leads and check the terminals for oxidation and then re-install to make sure they are fully seated. If you own a voltmeter you can test across those two terminals while the furnace is calling for heat,

 

i cleaned out the inducer motor tubes... and cleaned the ignitor sensor...
It did not want to turn on again... turned off power for ten minutes... it thought about restarting. turned it off again for ten minutes so that I could attempt to video tape what was happening... &
now it wants to work. I am convinced... it is possessed :-/

 

Make sure to check those connections on the inducer as suggested earlier. Also, shut off power to the furnace and remove the plug with all of the colored wires that attaches to the control board. Inspect the plug to make sure one of the pins is not sticking further out or further back than the other pins. Then re-install and make sure it is fully seated.

The drain hose I marked with the broken white line in the attached photo is the one that tends to clog up. Make sure that is clear all the way through by running water through it. It just pulls off at both ends.

 

Here is the control board... you are not talking about the thermo wires... but that other group of colored wires, correct?
that hose was checked yesterday! free and clear. There is a screw in the drain pan. It was on my list of replacement parts...
I will check those connections once again... the door switch black wire is a little jiggly. could that simple thing be the culprit?

 

Yes, the plug with the purple, blue and white at the top. Yes, the wire at the door switch can definitely cause the symptoms you are experiencing. That is the 120V feed to your furnace. Also, a loose ground wire in the service switch or in the electrical panel can cause those symptoms of intermittent operation. Definitely get that door switch wire tightened up and secure.

Were you able to find the leads from the inducer to the control board?

 

I checked the connections at the top on the gas valve and on the control board. All were tight and secure.

There is no ground wire in the service switch... hasn't been for at least 3 years, when it was moved, I don't know about before that... How do I tighten up that connector? or do i need to replace it? update* took a pair of pliers and gently squeezed the connector piece. now it is tight and secure. still having the same problem

further info... When I bought this house, it had the old cloth wiring. I have since run new romex 12-2 throughout the entire house. The only wire not replaced was from the conjuction box to the furnace (as it had just been rewired when it was moved). There was no ground wire on the existing bx cable (from conjunction box to furnace).

And again, I really and truly appreciate all the help you have given me!

 

Yes, a furnace depends on a good ground from the electrical panel into the junction box. I have attached a portion of the wiring diagram to show the required electrical service connections (top right of diagram). The complete wiring diagram is on page 58 of the installation manual linked earlier.

 

so it sounds as if I need to pull new wire through from the junction box to the switch box on the unit itself... that should be fun . and make sure there is a secure ground connection.

I wonder why it wasn't an issue in the past...

Is it possible that it is the gas valve?

 

A furnace will operate without the ground and there are probably millions of installations without one. Once you upgrade wiring (as you did) you are required to install the new according to current code. The grounding conductor is usually called the ground wire and is bare or has green insulation. It is for electrical safety in case there is a wiring fault inside the furnace. The stray or excessive current flow will go through the grounding conductor and the furnace metal parts will not be electrically energized - or "hot". This is a personal hazard as anyone who touches any exposed metal parts could be shocked. The grounding conductor also ensures that the stray current flow from an electrical fault will not go through the metal piping for the gas lines. If a fire was to occur, the insurance company would more than likely send an investigator to look at the electrical and gas connections to ensure they were done by the code and installed by a licensed professional. If not, they may deny the claim for loss. It really boils down to what your local jurisdiction adopts as the local code.

Getting back to your issue, it appears you may have a bad wiring connection since operation is intermittent.

 

here are the connecting points... the junction box, the furnace switch, and the inside of the furnace...

this is giving me a big headache lol

 

It is impossible to evaluate wiring connections from photos. How is the furnace performing at this point? Did you ever watch the flash code to see what it does when you call for heat?

 

I figured it would be.. but thought I'd post them anyway...
Furnace is making a humming sound indicating that there is power to it... but is useless beyond that.

The flash code does not change. steady flash throughout... the only thing it does is when i switch power back on to the unit, it flashes quickly (2x's) and then becomes steady after that

 

It sounds like a bad inducer motor. If the two terminals cited earlier are sending 120V to the inducer motor then the motor is more than likely bad. If the control board is not sending the 120V to the motor then the control board is bad. As you said, if it is humming that is an indicator power is getting to it. What is puzzling is why the control board is not throwing a flash code when it is shutting down. Did you feel the inducer motor to see if it feels hot?

I suggest you remove the inducer and see if there is anything lodged inside such as a dead bird or other object that might have come down through the vent pipe.

 

the unit is getting 120V as tested yesterday. The inducer motor did feel warmish. idk what it should normally feel like though.
With my limited knowledge of electronics... somewhere there is a glitch in the signaling. Hence the thought of it being the thermostat originally, lol... My next thought was the control board.

The furnace repair guy here insists that it is the gas valve... The other thought too was the inducer, but again when the system actually does start up, it works just fine...

 

Yes, but does it have 120V there when the inducer shuts off? The first thing that should happen when there is a call for heat is that the inducer should start up and it should continue to run until it shuts off when the thermostat is satisfied. As I understand it, the inducer does sometimes start and run and other times it doesn't. Did the "tech" test the gas valve?

 

you are correct in your understanding... when it feels like it...and there is a call to heat, it will start up and go through a cycle, then fail to start again for some unknown reason.

he did not.

I will dismantle the inducer tomorrow and see if there are any surprises in there. My guess is there is not as there was a movable vent cover protecting it.

 

You mentioned a 2 flash code. According to the chart that indicates a closed pressure switch. Have you checked to make sure the vent pipe is totally clear all the way through? If the pressure switch is closed the sequence of events will not begin? Do you have an air pipe coming into the furnace? If so, that entire pipe must be totally clear also.

Why would he suspect the gas valve and not test it?

 

it was very quick and only when turning the service switch back on. I will also check the vent pipes tomorrow...

He suspects that it is because all of the wiring goes in there and he claims they have a tendency to go bad... hence the reason I do not fully trust him.

 

I worked on a relative's furnace with a similar situation around three years ago. The inducer motor would start and then drop out. I tested the input voltage and was getting 120V to the inducer motor and then drop off to zero volts (motor would start/stop) or have zero voltage (motor would not start at all). I removed the control board and found two resistors showing evidence of high heat and cold solder joints. I re-flowed the solder, re-installed the board and all was well. If you don't have a voltmeter to test voltages there probably isn't much more you can do other than what has already been suggested.

 

short of throwing the thing out the window...
I don't mind replacing parts.. just dont want to needlessly replace them... I will borrow a volt meter and see if that is the problem.... Honestly my gut is that it is the control board or the lock switch...
At this point... I am ready to scream. I am trying to be as knowledgeable as possible because I hate it when people try to take advantage of me.

Thank you soooo very much. You have been most helpful!!! And at least now, I will know how to service this unit in the coming seasons, should I fix it, somehow, lol!!!

 

I was reviewing the wiring diagram again. It states that on some models the inducer motor has a run capacitor. Does yours have a run capacitor?

I totally agree with that. There is nothing more frustrating than replacing parts needlessly trying to chase a problem. It gets very expensive very quickly.

Not sure what a "lock switch" is. Once you test the voltage going to the inducer motor it will give you another clue as to what is going on.

Having technical knowledge about the furnace is definitely beneficial in many ways.