The 3A fuse blows on the main board when the bottom door switch is pushed
I have a GMH 951155DX furnace. The heat cycle works okay. When I switch to A/C and push the bottom door switch the 2A fuse on the main board blows. I put a new main board in. I removed the condensor two wires, I removed all the wires and plugged them one at a time, when I plugged the wire into the rollout sensor, it blew the fuse. I get 6 blinks, which says "bad fuse" or "rollout sensor open" I disconnected the wires to the thermostat, hooked them up one at a time, when I hooked the red wire the fuse blew. I replaced the thermostat, no help. This is a new installation, it did work for a while, I had a freon leak, when I repaired that, then the condensor would not come on, that is when I found the fuse blown.
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Re: The 3A fuse blows on the main board when the bottom...
There is definitely a short in the 24volt(low voltage) system. You have done the right things so far. I would begin by physically inspecting the wires for damage and performing continuity checks for each wire as well as each wire to the furnace. These checks should be done with a meter and disconnecting each wire at both ends.
Sometimes there is a very small bare spot touching the furnace or ductwork. You can diagnose this by checking continuity from the wire to the ductwork. If there is continuity then that is your problem.
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You may have multiple issues concerning the heat cycle, but the first that has to be resolved is the blowing fuse. The control circuit fuse blowing indicates a short somewhere in the low voltage wiring. IF the thermostat is newly installed, I would suggest first double checking ALL the low voltage wiring to make sure ALL the wires are connected correctly and to make sure the wire connected to the R terminal is not shorted to metal somewhere. If there is a C terminal, make sure R and C are not slightly bared and touching together.
Go to the furnace and note the location of the wires on the terminal strip. Remove them and install a TEMPORARY jumper across R and W. If the furnace comes on and begins the heat cycle without blowing the fuse, the problem is within the wiring or thermostat for sure. Remove the jumper and reinstall the wires. Go to the thermostat.
Remove the thermostat then take all the wires off of the sub base, taking note as to which wire went on which terminal. Take the R wire and the W wire and twist them together. The heater should come on indicating the problem is within the thermostat. Put the batteries in with a new fuse. If it blows, the sub base is the problem. If it doesn't blow, install the wire that goes to the R terminal. Check the fuse. Put the W wire on. Check the fuse. Put the G wire on. Check the fuse. Leave the thermostat on the chair, then turn the sub base 'fan on-auto' switch. Check the fuse. If its not blown by the time these three wires are installed, you inadvertently removed the 'short' by moving the wires around during this test. The remaining wires can be installed and the thermostat placed back on the sub base.
If you completed the above list and the fuse no longer blows and your furnace still only clicks, you obviously still have issues within the furnace of a mechanical nature. The clicking is the relays on the board initiating the combustion fan relay and attempting to initiate the pre-purge cycle. If the combustion fan hums and does not start, the fan could either be blocked (by a dead bird) or is mechanically shot and requires replacement. This fan HAS to start before the ignition process can begin. Solve that issue first after the blowing fuse issue is resolved. Its kinda rare that a system has so many issues at the same time. Usually when this is the case, someone replaced the thermostat and created that issue trying to resolve the underlying issue and the original cause for no heat.
This is NOT the professional way to troubleshoot it, but you are limited in your task without the proper analog or digital multimeter.
If you are unsure of your ability to systematically go through this process, abandon the idea and call a qualified service tech to bail you out.
You either have something wired wrong or you have a direct short in the system. Are you starting the A/C or the furnace? If it's the A/C, it could be a shorted compressor, capacitor, fan motor or it's wired wrong.
You may have a defective control board or blower motor. You will need to find on the main control board the location where the blower motor (marked heat) is connected. Using a volt meter, after resetting the limits and restarting unit, you will need to check and see if the board is supplying 1115 volts to blower motor (between the blower heat terminal and one of the neutral terminals on board). Also have someone hold in the door safety switch, or put a piece of tape on the switch, The switch will pop out when the bottom furnace door is removed, this is the normal location of control board. As the furnace goes through its normal cycle and prior to locking out on safety (limit opening) you should get 115 volts from the board (terminal marked blower / heat). If the board does not put out 115 volts, then the board is defective. If the board puts out 115 volts and the blower does not operate, the blower motor is probably defective, there is one more check to do. Close the door and put your system in cooling, see if the motor starts, if it does, then the low speed (reactor) is defective and motor needs replacing. If the motor does not start in cooling mode, you may have a defective capacitor. Check all of the above first and see what happens. Good luck, and be careful.
The switch you are talking about can be checked. Turn power off to unit. Disconnect wires on both terminals of this door switch. Next use a meter that will show Ohms or just connectivity to see if switch is closed when pressed all the way in. You could use a cheap meter from auto parts store to see if switchis good. You could remove switch and take to automotive parts store and they would actually check for you. If that device is good. Please follow wires from main power and see if there is a fuse before or on the main control board.. There will be a transformer that converts supply voltage to 24 or 28 volts and when turning power on that transformer will become warm and have a very small humming noise.. let me know what you find and if you need anything else.
I had a problem with goodman furnace/Heatpump thermostat circuit board blowing 3a fuses during first few months of using furnace about 3 years ago. Tech said it was not unusual and to replace it with a 4a. Have not had any problems with it since.
Code 12 I believe is power up after power off and a call for heat from the the thermostat. If you have a weak door switch that may be vibrating and going on and off it would cause this as would any thing that causes the power to drop low or out then reapply its self. try holding the door switch in while watching the board and after 2 or 3 minutes the furnace should go on to lite and the blower cycle off. If it stays in this mode try turning the thermostat off (heat - OFF -cool) and then push in the door switch nothing should happen except the lite on the board come on and stay on. If it does this than have someone turn the thermostat to heat and see if it starts or put the door on and set the heat and see if *** goes through the normal cycle of heating. If however it goes right back into the blower mode and shows the 12 code your problem is still with you. So next remove the wire on the "W" terminal on the board. Retry power to the door switch and now nothing should be on except the red lite. If it tries to start the 12 code and blower up again Im pretty sure you have a bad ignition/blower control board.
I would suspect you have a problem in the defrost circuit of your heat pump. there are a couple of things you can try. first just run the system on emergency heat and see what happens. you could have a defrost board that is shorting when it kicks into defrost. it sends a signal back to the furnace so it will come on during defrost. if you do not blow a fuse as long as you are running in emergency heat, i would suspect the defrost control board. also you could have a dead short in the wire that runs from the "w" terminal on furnace control board, out to the heat pump. keep in mind that any of the wires could be the cause and i am just tying to give you the most common things. your furnace will still run if you unhook all the low voltage wiring out at the heat pump. if you do this and stop blowing fuses. you know it is something on that wiring. goodl luck.
Hi!!! Does your ac unit work fine?If not check your low voltage problem..You have a low voltage problem check the wire going out to your condensor make sure that they are not touching..Good luck..Check low voltage wires..short in progress..
These new furnaces are trouble. Ive been in the htg trade for 25 yrs. The fan is running because they are now controlled by a timer instead of a temperature control. Rather than sensing a preset temperature and turning on the fan, it comes on by a preset time. Couple of things, does either of the doors have an inspection window? most newer furnaces have what is called a smart board. The board will flash a trouble code. ie: 1 long 2 short etc. #1 turn your thermostat to off, youll need 2 people for this! Go to the furnace, If it has the above mentioned inspection window ( usually about 2" round) while peering through the window have someone turn the thermostat to about 80 degrees. Let the furnace cycle and see if it flashes a code. If it does the codes are usually on the bottom door, May be on the inside. The most common cause is either a bad transformer, bad hot surface ignitor or pressure switch failure. Further questions feel free to ask. Steve