I am on my third failed Control board (B18099-23) for a Goodman GSU100-4 Furnace

Board #1 has been working fine so far this winder but something is wrong with my system as it quit working last night.

Here is the issues I have with the two boards.

Board #1
Thermostat calls for heat.
Draft Motor starts.
After about 20 seconds, Furnace fires and burns.
After about 5 seconds flame goes out.
Draft motor keeps running.
NO HEAT
Lite on board is constant

Board #2
Thermostat calls for heat.
Draft Motor starts.
After about 20 seconds, Furnace fires and burns.
Furnace runs and works until thermostat reaches temp.
Fire stops burning. And shuts blower off
Draft motor keeps running and running and running. Will not turn off.
Furnace will not fire again until I kill the power and the cycle starts starts all over again.
Lite on board is constant

On this board #2I see that a relay appears to be damaged and plan on replacing it. I would like to know why these boards keep failing for me. I called the Goodman company will not give me the info I need to figure out what is wrong. They say I need to speak to a licensed repair person. I would like to know what is wrong and what part to replace on the control board.

I am using board #2 until I get a replacement relay that I ordered, I hope this fixes it. Otherwise I'll need to buy another board. But I'm sure that one will fail like all the rest. Anybody have any ideas?

I never replace the parts on the control boards because many times the parts are not easy to find if not impossible to find under some circumstances. Board number one seems to be a candidate for a flame sensor cleaning since it is droping out in short order after it lights.

Other style of flame sensor. Easy does it on this one since the ignitor is close and they break easy.

Thanks for the reply. I can find the relay in a electronics supply catalog. Only$1.50 for the part where the board is $200. (I'm a ex electronic tech)

Board #1 is the one that was running fine and had to pull out and put my last board #2 back in just because it still will run the furnace. I just have to cycle the power on and off.

So that has me thinking that it is not the flame sensor. Why would it work for one board but not another.

Lets answer it this way. Nothing ventured nothing gained. You basically have two defective boards according to your diagnosis and you are on your third board total. All I can say is something is wrong with this picture because boards usually do not fail that often and how do I know this? We test them for the manufactures at the university and why do we do this sort of testing along with testing complete HVAC units? To make a few $$$ so we can continue to buy our testing toys for classes.

You can fix your own board that is just fine but for a tech to fix a board for a customer is a major law suit waiting to happen. Seven out of 10 circuit boards returned for warranty are not defective those are the facts.

Not for a customer. It's my own home furnace.

LED is Steady On ON • Normal Operation > from the Goodman manual

Is the light on steady or is it blinking all the time?

As you mentioned.

"All I can say is something is wrong with this picture because boards usually do not fail that often"

That's why I was hoping somebody could help me figure out why all these boards seem to fail the same way.

The boards seem to fail or not work correctly when the 120 volt supply is not attached correctly and in the placement of the neutral White wire and the line Black wire if they are reversed in the wiring system from the panel to the furnace etc.

They also do not like it if the green or bare ground wire is not connected properly from the main electric panel to the furnace then to the boards ground.

They will also not work properly when the low 24 volt side conductors are reversed from the transformer to the board. This is what most professionals find in the field and this is what we have found when testing the circuit boards that are returned by the distributers. When we trace the boards back we usually find homeowners tried to install the board or stupid HVAC mechanics that think they know what they are doing did. This is the reason of the relative new policy of NO electrical part returns unless it was installed by a dealer or heating professional. This new policy will stop the home owners from costing the manufactures a bunch of money losses.

Well I will need to go over the wiring and look it over. If that is the case this thing has been incorrectly wired for 9 years when the furnace was installed. Thanks for the help.

Not sure if this would help but the relay that appears to be damaged on Board #2 is a 12V T7CS5D-12

Not sure if this would help but the relay that appears to be damaged on Board #2 is a 12V T7CS5D-12

I never replace relays since I never have the time to play with them but if you have the time go for it since it is cheaper than a board. I have seen the covers melted right of the relays before. They are all cheap parts made in china. LOL

The diagnostics on these boards are not super-reliable. They can be fooled by partial voltage, the most common "trick" I have seen occurs as the result of a faulty pressure switch. Enough voltage is present to tell the board it is engaged, but the contacts won't support the necessary current to allow the other components to function.

Well I was successful with changing out the relay. Furnace works like it should. Inducer does not run all the time.

I then went the next step to try and figure out why the relay failed by checking the wiring. The only thing I did notice is that the blower motor was wired strangely. It worked but I went and followed the wiring diagram.

Diagram calls for
Black - Cool
Blue - Heat Med.
Red - Heat Lo

Blower Motor WAS wired
Black - Cool
Blue - Heat 1
Red - M1 (unused)

Since the board doesnot have a terminal labeled as Heat Lo or Heat Med they are labeled as Heat1 and Heat 2. I went and wired it this way. It works but I would like to know if this is correct. Should the Blue and Red be switched or is this correct?

Black - Cool
Blue - Heat 2
Red - Heat 1

Heat usually runs on the lowest speed as long as there is enough air movement to keep the furnace within its labeled heat rise rate as posted on the furnace label. That you can check with a thermometer by checking the difference between the air entering the furnace and the heated air leaving the furnace. That is the proper way to adjust the speed for heat.

As far as what color (speed ) goes to what terminal it does not make a difference as long as the correct speed is chosen for the proper operation of the furnace as mentioned above.

NOTE: It could be that you furnace and duct work needed the MED speed (as originally wired) to perform within the specifications of the furnace as mentioned before. Do NOT change the blower motor speed wiring unless you test as mentioned above and find the (Red) low speed will work within the design temp rise of the furnace.

Blower speed appears to be the same. I guess the question I would like to know is whether Heat 1 would be considered Heat Lo and Heat 2 is Heat Med.

The blower speed is determined by the color of the motor wire since that color is tapped into the windings of the motor in a different area allowing for a different speed. I am going to say that heat 1 would be the low speed next step is heat 2. If you can find out the exact manufacturer of the board you might be able to get more specific info.

I'm going to send Goodman a note asking just that. We'll see if they answer.

Thanks Again!

They might answer. I never found it to be a problem since I always setup the blowers using the temperature method. Which ever terminal supplied power in the heat mode only was the one I always used. I believe you will find this is your wiring diagram w/board. Now in this case with a 2 stage unit there could be a need for the medium speed.

http://www.myhvacparts.com/Catalogue/Printed%20Circuit%20Boards/Goodma2.jpg

Yup that's the diagram I have. IDB Indoor Blower wires are the ones in question. I sent Goodman a note, We'll see if they answer. In the mean time everything is working. Still puzzled why the relays failed. I'm hoping the change in wiring that I made will cure.

Got the standard reply from Goodman, "Please Contact a Licensed Repairman" Blah Blah Blah.

That is the standard reply for all manufactures in the HVAC trade.

Same furnace different problem now. Limit switch went out. It had a Texas Instruments L170-30 7 inch switch. What I found odd was that the middle of the switch had what looks like burn marks and some cracking from appears to be too much heat. When I contacted the local furnace guy he was surprised that it used a 7" switch and not a 3". With the burn marks I begin to wonder if it's right. My Furnace guy was not able to find a L170-30 so I have a 7" L160-30 installed.

I was having a hard time even locating info on this furnace. Anyone have access to figure out what the correct switch should be?

Same furnace different problem now. Limit switch went out. It had a Texas Instruments L170-30 7 inch switch. What I found odd was that the middle of the switch had what looks like burn marks and some cracking from appears to be too much heat. When I contacted the local furnace guy he was surprised that it used a 7" switch and not a 3". With the burn marks I begin to wonder if it's right. My Furnace guy was not able to find a L170-30 so I have a 7" L160-30 installed.

I was having a hard time even locating info on this furnace. Anyone have access to figure out what the correct switch should be?