Your friend's work around with the thermal switch sounds as if it was in lieu of a third stage on your thermostat. Honeywell makes a three stage thermostat (3 heat - 2 cool) The TH8110U that would do that for you. And there are others. A bit of an expense though, considering that what you have essentially accomplishes the same thing.

I too am having the same problem and very similar to Sparky. I too have a Goodman unit that was installed about 4 years ago and the outdoor unit replaced again after a year and it failed. I too have just noticed cold air blowing out and apparently it is during the defrost cycle. I put a hout thermometer on it and it will normally run around 84 degrees at the register but at times will run about 68 degrees. The temp outside has benn mid 20s to mid 30s. The furnace guy came out and said the filter was plugged and had kicked out the heat strips. I questioned this, but figured he knew what he was doing. After he left if continued to happen and had him out again. He 'added' a board to turn the unit off during defrost. Doesnt sound like that can be done from what I read. In any case he left and the unit continues to do the same thing. It sounds to me that the heat strip must not be coming on during defrost. What part that might be is probably the question. Does anyone know if the heatstrips have an interanl 'breaker' or theraml cuttoff. I know I checked the breakers back at the panel and the breakers on the indoor unit and they were normal before the heater guy showed up and told me he had to reset these. Any thoughts or possible solutions from the others that are experiencing the problems please let me know.

Just took apart the heating element part of my Asko T760 dryer for first time in 18 years - it had been shutting down for overheating when heat was on normal (vs. low heat). wow. Manual does not list a lint covered heating element as a potential cause, but it totally was. Lint was blocking all air flow and clogging the heating coils. Evidence of burning (burnt lint) on the coils. Now running on normal dry cycle with my Klein Tools Multimeter with temperature sensor in the exhaust duct and it is 117, even though manual shows heating cycle should be up to 131-135, so maybe I have one heating coil / element burned out? Either way, it runs way cooler than before when it would shut itself down at exit temperature of 127 degrees. This was a big clean of an area that really is not mentioned, other than when you look it up in the manual, for replacement of the heating element, it says after it describes the taking apart of the dryer to the point of the heating element, that you can replace it or clean it. After seeing what I saw, it would certainly be listed as a potential cause of overheating shutoffs. Cleaning recommended.

HU-373650237, Can you tell what speed the fan is running in when it comes on with the T'stat off? High speed is used for fan on and A/c, and low speed for heat. If you say the fan runs in high speed the problem is in the "Fan on or A/C circuit. The only way the blower can run in high speed is if the Heat/cooling relay on the white rogers board is energized to close the contact supplying high voltage to the blower motor's high speed tap. So as mike suggested you need to measure the voltage of the "G" wire disconnected from the furnace control board along with pulling the "Y" and "W" wire. The "G" and "Y" are connected together in the thermostat when the fan is in auto so you want to totally isolate the thermostat from everything else. Connect the red to the "G" wire and the black to a ground, basically any metal part of the furnace. The Push switch right above on the frame can now be pushed in and held or taped to turn the furnace on. Any voltage will indicate leakage and be suspect. The Heat/cooling relay holding coil is really a current operating device and doesn't need 24Vac to energize the coil, but only enough voltage with just enough current to energize it. Here's where it gets tricky, Just because there is enough voltage/current to energize the coil doesn't mean there's enough to hold it energized for long. As the coil temperature heats up from current running through it the coil resistance increases, and the voltage/current draw will also increase to a point the relay coil will drop out and the blower stops. When the coil cools the process starts over. Even a low voltage will indicate leakage (short) somewhere in the T'stat or wires to the T'stat. Stick with me, If the fan runs in high and testing the T'stat circuit showed no voltage on your meter I have another test for you to do. Let the power button on the frame turn off the power and with all the wires "G", "Y" and "W" still disconnected from the main board do the following WITHOUT power on at the furnace. Check the voltage across the "W" terminal on the furnace control board and ground. Any voltage at all will indicate the compressor contactor in the condenser is leaking voltage/current back feeding the Heat/cooling relay. If so go turn off the power to the condenser and recheck the voltage drop across the "W" terminal again, it should be zero. If that's the problem go into the condenser and clean the dirt and cobwebs off the contactor with the power OFF! What you just checked are the only components in the fan on and A/C circuit that could energize the heat/cool relay to cause the fan to come on in high speed. If it comes on in low speed then it's in the heating electrical/electronics size and another story. I found most of the wiring diagram for your unit and was able to confirm what I just said. If you do find the problem please tell us, I'd love to here back. For reference the high temp limit is the black plastic plate right of the gas valve but PLEASE do not mess with it at this time. It's a critical safety component and if the fan runs in the off position it is not involved so leave it alone and I'm sorry I mentioned it.