Furnace Blower Fan Cycles On/Off During the off Cycle

[capwizard]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

Roll out temperature switch is 350F and the temperature bending circular metal, letters on top are E3.
So I decoded this (3) is for 300, (E) is for 50 .....so is 350F.....? and 280F will be marked H2, 250F will be E2 ?

[petehall347]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

Maybe Relay control circuit, on PCB has two Trs, as I tested they are Darlington Transistors, daytime maybe trigger the high gain Darlington Transistor to turn on because the dirt from water mark.

PS: cant find any information about this two Trs?

yes they could possibly turn on if tracking can occur .. are these just drivers for relays ? or some other job ?

[Longbow]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

Ok, the control board was faulty. A couple of comments. First has to do with 200 furnaces in your neighborhood. With a little more checking around the motor speed wires, you might have an idea about what part of the board failed. Then, you can drop a note to all 200 people who need the same repair. Second, you might stumble on a bad part on the board - maybe. Furnace control boards are hard to diagnose if it is subtle, since no schematics exist except in the factory. Also, many models of HVAC control boards were immediately updated once the manufacturer realized he did something stupid. It is wise to check out this possibility if you can.

I agree that high gain darlingtons would not be my choice in a furnace. At over hfe 1000 a lot can happen when they warm up. Besides everything is vibrating its brains out on every blower cycle. If you find anything specific, let us know.

[capwizard]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

I forgot upload the pictures of Roll out temperature switch......................

[capwizard]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

Maybe Relay control circuit, on PCB has two Trs, as I tested they are Darlington Transistors, daytime maybe trigger the high gain Darlington Transistor to turn on because the dirt from water mark.

PS: cant find any information about this two Trs?

[capwizard]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

I almost forgot one thing. The roll out temperature switches.

PS: To whom might find interesting, Roll out temperature switch, the temperature bending circular metal, letters on top are E3, some kinda temperature rating.

PS: I just trying to show, I still have some value for someone in this world.............

[petehall347]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

well done

[stj]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

probably a bad relay.

[capwizard]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

[vinceroger69]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

Sorry, I haven't had a HVAC licence. so I can fix mine or friends's only....and i'm too old for that......

main thing is its working and another job completed.

[capwizard]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

Sorry, I haven't had a HVAC licence. so I can fix mine or friends's only....and i'm too old for that......

[vinceroger69]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

the main thing is you have sorted the issue out and another happy customer who should refer you to friends family etc so maybe even more work in the future.

[capwizard]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

Goodman model NO. GMP075-4 :the blower motor runs erratically, especially at day time even took out the thermostats. But when I set up thermostat to heat, the burner works flawless. After changed new PCB it stops the problem.

PS: I found an easy way to fix the problem, just ask the neighbors, About 200 peoples in the community use the same furnaces and use same systems.

GMP075-4
https://cdn.badcaps-static.com/pdfs/...e2ee1acf8b.pdf

[srhofmann]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

Furnace's PCB , A EPROM/ROM-Based 8-bit CMOS Microcontroller, designed to start up furnace's sequences, it drives circuits, sensors and relays.

PS: Why !! It is not work still in further investigation......

PIC16C57C
This powerful (100 nanosecond instruction execution) yet easy-to-program (only 33 single word instructions) CMOS OTP-based 8-bit microcontroller packs Microchip's powerful PIC® architecture into a 28-pin package. Easily adapted for automotive, industrial, appliances and consumer entry-level product applications.
https://cdn.badcaps-static.com/pdfs/...88d10b865b.pdf

The 16 pins IC is ULN200x High-Voltage, High-Current Darlington Transistor Arrays. To drive relays.
https://cdn.badcaps-static.com/pdfs/...2f9b2d5b4e.pdf

What isn't working? The new board or the old board? And what are the symptoms?

[keeney123]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

Furnace's PCB , A EPROM/ROM-Based 8-bit CMOS Microcontroller, designed to start up furnace's sequences, it drives circuits, sensors and relays.

PS: Why !! It is not work still in further investigation......

PIC16C57C
This powerful (100 nanosecond instruction execution) yet easy-to-program (only 33 single word instructions) CMOS OTP-based 8-bit microcontroller packs Microchip's powerful PIC® architecture into a 28-pin package. Easily adapted for automotive, industrial, appliances and consumer entry-level product applications.
https://cdn.badcaps-static.com/pdfs/...88d10b865b.pdf

The 16 pins IC is ULN200x High-Voltage, High-Current Darlington Transistor Arrays. To drive relays.
https://cdn.badcaps-static.com/pdfs/...2f9b2d5b4e.pdf

So what is the brand and model of the furnace? Do you have a wiring diagram for the furnace?

[capwizard]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

Furnace's PCB , A EPROM/ROM-Based 8-bit CMOS Microcontroller, designed to start up furnace's sequences, it drives circuits, sensors and relays.

PS: Why !! It is not work still in further investigation......

PIC16C57C
This powerful (100 nanosecond instruction execution) yet easy-to-program (only 33 single word instructions) CMOS OTP-based 8-bit microcontroller packs Microchip’s powerful PIC® architecture into a 28-pin package. Easily adapted for automotive, industrial, appliances and consumer entry-level product applications.
https://cdn.badcaps-static.com/pdfs/...88d10b865b.pdf

The 16 pins IC is ULN200x High-Voltage, High-Current Darlington Transistor Arrays. To drive relays.
https://cdn.badcaps-static.com/pdfs/...2f9b2d5b4e.pdf

[capwizard]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

Thanks to everyone who participated this Thread.....YES ...I fixed it.....by changing the control PCB of which I thought is unlikely to be ......so far so good......I will need at least three days to test system to make sure furnace work flawless .......

PS: when furnace lit up look like the Apollo 13 launch to the sky.
PS: I use discard wires as a zip ties, the easy ways to recycle......

[srhofmann]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

Longbow,

It's not the cap and it's not loose solder connections on the relays. There's an underlying issue either with the sensor(s) circuits or the board, because he's getting blink codes.

Once the blink code issue is resolved then we need to see what happens. He has a plain simple 3 speed blower motor and something is telling it to turn on when it should be off. The control board in a failure condition, either the board failing itself or something that causes blink codes, can call for the blower and/or inducer fans to turn on even with the thermostat in the off position.

[Longbow]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

Reality check, refer to the furnace manual posted on the first post. There are 2 styles of motors used on this furnace. One style of GMP uses a standard 3 speed motor. This series should be straightforward to troubleshoot, especially when we find out which speed is coming on during the intermittent operation.

The GMP models ending with "E" actually have electronic, or "ECM" motors that have electronically controlled speed (infinite). That series will have a more complex control board and more expensive motor. So, once again it appears we are dealing with a standard 3 speed motor as per your description above?

Next, flip through the .pdf you posted and determine which of the 12 GMP diagrams apply to your present furnace - that would certainly help. If in fact you have a 3-speed motor, the most common failures are going to be 1)motor capacitor and 2)loose solder connections on the pcb motor relay terminals. The order of troubleshooting steps matters.

So, what kind of motor? Which diagram? What speed is intermittently coming on and off?

[Longbow]

Re: Furnace Blower Fan Cycles On/Off During the off Cycle

"Is this the switch you are talking about?" .........Yes.
"when the fan turns on by itself, what speed does it run?"...... no sure but pretty fast

Well, find out which speed it is running before doing any other troubleshooting. The point we are missing here is the METHOD. Don't skip around from guess to guess. You are no further along than when you started - so don't become an HVAC technician!

"If FAN ONLY switch is ON, what happens?" the fan blower turns on.

I guess you mean that the fan turns on and stays on. If so, what speed does the fan run at when you flip the FAN ONLY switch on? Important!