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-   -   Goodman GMNT 080-4 inducer problem (http://www.diychatroom.com/f17/goodman-gmnt-080-4-inducer-problem-99527/)

RiccH 03-25-2011 01:42 PM

Goodman GMNT 080-4 inducer problem
 
a couple months ago I had a service tech come in as my furnace was making a loud whirring noise on startup (Loud enough to wake me at night!!) He said the inducer motor was bad. It's rated at 1.8 amps and he showed me is amp meter and it said it was running between 4-5amps. He suggested it needed replacement as anything plus or minus 10% of the rated amps wasn't good. I took his recommendation had him replace it. the new inducer motor was nice and quiet for about one week then started to make noise again. The tech came out at no charge to recheck and said the replacement was pulling too many amp. He then checked the exhaust pipe for an obstruction and for proper angle and all was good there but said the new inducer may be defective from manufacturing. I asked if there was something else wrong with the furnace causing the inducer motors to fail prematurely. He said there wasn't. (Note; this tech worked for Sear for 20yrs installing/reparing furnaces and appliances so I thought he knew his stuff) He got it replaced from the supplier at no charge.and the new motor ran at 1.8amps as specified.

Here is is 2 months later and again it is making a loud whirring noise. Since i had watched him do the testing the last two times I borrowed a clamp on amp meter and found that the inducer is running between 3.5-6 amps up and down. the motor is also very hot to the touch.

Any ideas on what to do? Should I replace it again after only two months. Could there be something else wrong causing the inducer to run hot and at high amps? Anyone in Elkhart, IN who wants to come check it out??

Thanks
Ricc Havens
Elkhart, IN
rv.havens@gmail.com

hvactech126 03-25-2011 03:19 PM

check the voltage. probably low. Check the connections at the control board and the inducer. Check the voltage coming in to the unit. check the voltage across the door switch.

Doc Holliday 03-25-2011 03:21 PM

Oh, a touchy problem. I'd like to take a stab at it but mind you this is a learning stab at it, I've never come across this problem before. Something is definately giving this thing too much voltage or not enough restriction and it's running too freely.

I'd check the voltage to the inducer motor and see if it's not leaking more than allowed so if it's rated 120 volts it shouldn't be receiving 130. If it is than it could be a control board problem, on it's way out. It could be that the entire unit is receiving more voltage than rated for, I honestly don't know.

I'm not sure if that would cause an electrical motor to pull higher than allowable amperage, feeding it more voltage, it's only a guess.

Perhaps an electrician could step in and help out with my theory.

Either way, please report back and let me know when you do find out, it'll help me if I ever come across this problem.

RiccH 03-25-2011 03:37 PM

Doc, just went and checked the voltage as you recommended. It is rated at 115v according to the label and reads 118v on my multitester

Thanks
Ricc

Doc Holliday 03-25-2011 03:45 PM

I'll be right back, taking this to an electrical forum to ask. Give me a few minutes and I'll find out if 3 volts can affect the amp draw.

hvactech126 03-25-2011 03:49 PM

no, 3 volts will not affect it in that way! There is another issue. While you were reading the voltage do you know what the amp draw was? Was it going up and down at that time? Also, how far away was the meter from the motor while taking the reading? If it is right next to the motor while taking the reading you can get unreliable readings due to the magnetic field near the motor that the motor creates while in use.

RiccH 03-25-2011 04:20 PM

Hvactech, I had the clamp on amp part of the meter 6-8in away from the inducer and the body of the amp meter hanging outside the furnace casing. that's the farthest I could get with the wires on the inducer motor.

I got my multitester out while the borrowed clamp on meter was on the wire. My digital multitester showed 120v while the digital amp meter fluctuated between 4.6 to 4.7 amps

Ricc

Doc Holliday 03-25-2011 05:00 PM

Okay, I asked and as suspected and as already stated by tech126, 3 amps will not make a difference. That now leaves an air flow problem as not enough suction to pull that motor back to stay at 1.8 amps or close to it.

The inducer motor pulls in a pressure switch, closing it, which ensures that there is proper pressure for the flames to be pulled through the heat exchanger.

My guess now would be and again, IF this inducer motors act in the same manner as certain blower motors which need and depend on air restriction or they will ramp up and pull more amps freely, is that the pressure switch or a tube connecting to the presure switch from the inducer (the air pulled from the inducer sucks the pressure switch closed through the heat exchanger) is going bad. It, the vinyl tubing, simply could be getting too hot and expanding and coming loose enough to allow air to move freely somewhere or the switch itself could be on it's last leg. The tubing could simply have a hole in it as well, expanding and contracting due to the heat as well.

These are my guesstimates from sitting here but nothing else I could think of could be the problem. It can't be the board going bad as it's sending the required voltage to the inducer and 3 volts over is nothing out of the ordinary and again, would not cause the motor to pull more amps.


Or your heat exchanger could have a small crack that is slowly getting bigger. That would mean that when the heat exhanger is hot it is allowing more air to flow freely through the inducer as the metal is expanding which could allow for it to ramp up, pulling more amps. When that metal cools off a bit and restricts the crack, the smaller crack makes more of a restriction (as per design as no air from outside of the heat exchanger should be pulled in, closed system, but if cracked than yes) and thus the amp draw goes down. And back and forth we go.

These are my internet service tech guesses and I hope they help.

Doc Holliday 03-25-2011 05:03 PM

or the inducer could simply not be seated correctly, just like a tube may be not seated correctly, and is allowing more air to flow.

guessing. spent.

RiccH 03-25-2011 05:41 PM

Doc, I don't know if that would be the issue. It would seem to me if that was the issue the it would have happened from day 1 of the replacement of the inducer. the first time it was replaced the inducer was quiet for about a week. Then when the service tech replaced the inducer under warranty it was nice and quiet for a little over two months. I could be wrong since I am not a tech but I would think if it was the pressure issue or a cracked exchanger causing a pressure issue it would make the inducer act up right away not a couple months later.

Ricc

hvactech126 03-25-2011 05:46 PM

Doc brought up a point that I forgot to mention. YOUR FURNACE IS KNOWN FOR HEAT EXCHANGER FAILURES. I do not believe ,however, that is related to the concern of your inducer. The heat exchanger does need to be examined by a professional during it's yearly prescribed maintenance per the manufacturer. The heat exchanger is a separate issue but you do need to take that into consideration before putting any more money into this furnace! Without being there, I'm having trouble coming up with other ideas as what might be causing the problem other than intermittent voltage drops or spikes.

RiccH 03-25-2011 05:53 PM

Hvachtech, I am not sure if I have an issue with the exchanger. The service tech did look the whole furnace over originally back in January when he first came. He even used a gas leak detector to check for gas leaks. Wouldn't a gas leak start to show up if I had a heat exchanger issue?

Ricc

hvactech126 03-25-2011 06:02 PM

no. a gas leak would be a combustible gas. Carbon monoxide is odorless and would need a CO detector or combustion analyzer to determine if it were present. and It may not even be present even though the HE is cracked. IF the HE is cracked it leaves the possibility for CO to leak out. It does not mean the CO is leaking out of the HE.

back to the inducer....... You are pulling double the rated amps. This is a cause for concern. Motors don't just start doing that unless there is something to make them start doing that. IE voltage issue, capacitor (if the motor uses one, yours probably does not) issue, air flow issue (should be detected by a properly operating pressure switch).

yuri 03-25-2011 06:29 PM

The inducer fan relay on your circuit board may be failing, have a failing solder joint or pitted contacts and is causing it to over amp just like burnt contacts on a AC contactor. I know the voltage should drop but I have seen 110 volt toggle switches/power switches to furnaces fail/arc and with a sensitive digital meter you can still read 110 volts. Sounds like this may be the common denonimator all along and yes the boards of that particular unit I have changed a lot of. They can also burn out and do some weird things if the bracket the board mounts on to the fan with comes loose. Causes them to lose ground and burn out. Need to put more or bigger sheet metal screws in it.

Marty S. 03-25-2011 07:02 PM

I'd call the guy back and let him put a third in. No sence paying for a part when it's under warranty. Heck the labor might be covered too, we give a year. Is he replacing the whole assembly or just the motor? Those things spin at 3000 rpm so an out of balance wheel will wear on bearings fast.


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