Goodman furnace 4 blinks

There should be a diagnostic chart on the furnace door by the wiring schematic. If so see what the code reads for three blinks.
By the term "air combustion switch" I guess you are referring to the pressure switch. Most diagnostics blinking three times is just a dirty flame sensor. If this is the case the burners will light and go out within 4 seconds. If this is the problem carefully remove the flame sensor and clean gently with emery cloth, fine sandpaper or fine steel wool. Reinsert the sensor and enjoy your heat.

There should be a chart pasted to the inside of the front access panel of the furnace. It will tell us what that particular blinking sequence means. Goodman isn't listing a gmp125-4 furnace so I need to assume it is a condensing gas furnace. I water has backed up into the draft inducing fan, the furnace will shut down. There is no reason for water dripping from the drain pan unless your A/C is running and the drain on the pan is plugged. Give me all the info. you can and exactly what is happening. Please look up the coded problem for me. I'll watch for your reply. I hope this is not too late to help.

This model is equiped with a diagnostic error control. Take off the front panels and look for a wiring diagram pasted on the reverse side of the panels. On this diagram there will be a chart telling you what 4 blinks represent and where to start looking for the issue. I suspect the air filter may be dirty or the pressure switch may be bad, however make sure the condensate hoses are free of any debris. Good luck to you!

This unit is equiped with a diagnostic light and will blink a number of times indicating where to start looking for the problem. Find a small viewing port that looks right on to the control board. Count the number of blinks. Then find the wiring diagram and there will be a diagnostic chart where you can compare what the number of blinks represent. Let us know what you find.

If you look thru a small viewing window, you will notice a small LED light blinking. Count the blinks and then remove the front access panel. On the reverse side you should find a diagnostic chart indicating what could be the issue based on the number of blinks.

first, clean the flame sensor, does the draft motor come on?  could be ignition control board failure

This furnace has a diagnostic light on the control board found in the lower section of the furnace. Pilots are a thing of the past and your system has a glow ignitor. Look thru a small viewing port to see how many blinks are being displayed. Then remove the access panel and on the reverse side of it is a diagnostic chart that will tell you where to start looking. I would suggest you make sure the air filter is clean and that the condensation is being removed. Recycle the furnace with either the breaker or emergency switch. You can cycle the furnace with the front cover off if you tape the door switch closed. It may be easier to view the sequence of operation to pick up on where the fault is occuring.

You could have a limit switch that opened. On the reverse side of the furnace access panel there will be a diagnostic chart indicating what 4 flashes indicate. If it is an open circuit, why is it open? Did the unit get too hot and why? Unless you have the diagnostic capabilities, call a professional.

OK, we will need to perform a simple test of the furnace to see exactly what is going on. Set your thermostat to 10 degrees higher than you normally do so we know that there is a call for heat. Then at the furnace, there will ba a small viewing port. Watch the blinking light and record all the patterns it blinks. After a minute or so, place your hand on the PVC vent pipe(s) to see if they are warm. If not, either the thermostat is not sending a signal to the furnace or we will need to look inside the furnace to see what is happening. But if one of the PVC pipes is getting warm, place your hand on the plenum on top of the furnace connected to the ductwork. You shoul feel the metal starting to get warm. If the blower does not turn on within two minutes, there is an issue with either the blower itself or the control board.

Getting back to if one of the vent pipe(s) don't get warm. Using a piece of duct tape or electrical tape, after removing the furnace access panel, tape the door safety switch down. The furnace will now try and cycle. A small fan attached to the vent pipe should run, then it will create suction on a pressure switch that will energize the ignitor. You will notice an orange glow thru a larger viewing port looking into the burner box. After a few seconds, the gas valve will open and the ignitor will ignite the gas. The orange glow will turn to a blue flame. Now after two minutes or less, the blower should turn on. If one of these steps don't happen, you should document it and let your technician know. As far as the blinking lights, these are diagnostic codes that will tell you where to look for the issue. On the rerverse of the access panel, there is a chart that gives a simple explanation of what the blinking represents. Again, let your technician know what you discovered. Keep in mind that the furnace will cycle or attempt to start 3 times before it will blink an error code.

Remove the tape and reassemble the access panel. Yes you will need to contact your technician but the steps you performed just saved you 30-40 minutes of diagnostic time.

Is there a diagnostic chart either on the reverse side of the blower door or in your owners manual. It may help you to narrow down what is going wrong.

Operate the furnace with the access door off of the furnace and the blower door switch taped on. Watch the furnace and document what happens. Note if the flame starts but goes out in a few seconds and let me know what you experienced.