I have a Maytag refrigerator with french doors and a bottom freezer. Model # MFI2568AEB and Serial # 12516299LR. The freezer and refrigerator do not get cold. I can feel the heater on in the door of the refrigerator. I'm assuming this is the defrost heater, it is always on. How do I determine what the problem is?

Here are the manuals: https://dl.dropbox.com/u/8010163/Maytag%20Refrigerators.zip
The first thing you need to do is to check the coils under the unit and wash them out along with the fan blades. Use spray soap and water from a hose nozzle to wash out the coils. Defrost it well by opening freezer and washing out inside coils to remove all ice. Then see if after you put back rear cover and start it back up if it cools. If it stops cooling after about three days you know something is wrong with the defrost system. It could be the defrost heater which you will have to check with a meter. Let us know what you find.

Here are the manuals: https://dl.dropbox.com/u/8010163/Maytag%20Refrigerators.zip
The first thing you need to do is to check the coils under the unit and wash them out along with the fan blades. Use spray soap and water from a hose nozzle to wash out the coils. Defrost it well by opening freezer and washing out inside coils to remove all ice. Then see if after you put back rear cover and start it back up if it cools. If it stops cooling after about three days you know something is wrong with the defrost system. It could be the defrost heater which you will have to check with a meter. Let us know what you find.

There isn't any ice build up at all. The compressor is working and the fan is working. Neither the freezer nor the refrigerator get cold. The left side door has a hinged panel that must have a heater located inside that is always hot. I have a Fluke meter. Where do I test the defrost heater and am I looking for ohms or voltage?

If you have no ice buildup make sure to check the lines on the compressor. The larger line is the suction line and should be cool or cold and the smaller line is the hot gas line which should be hot. If this is not the case and the compressor is running it could be that the compressor has bad valves, or the unit has hot gas defrost and the defrost valve is stuck halfway. Your unit has a regular defrost system, however, I believe unless it's a newer modification. Check this out and write back. I suspect a bad compressor.

I have checked the compressor lines. The suction line and the discharge line feel about the same temperature. I suspect a leak in the compressor discharge tube to the condenser. There is some corrosion on the copper discharge line with a greenish discoloration. I have completed the on board diagnostics in service mode. Service test 101 is the defrost heater and circuit. The display reads OP (open defrost thermostat). Any further direction would be greatly appreciated.

That does not sound like a leak. Look for oil. All Freon has oil in it so it often leaves oil at a leak. If the lines are about the same temp it could be a leak, bad valves, or a no load situation. In order to know you should attach gauges and have a leak detector like a De-Tec leak detector. An open defrost t-stat would also cause the same symptoms if it was running while the evaporator was full of ice it's in a no load situation. You should also check the defrost heater because the defrost t-stat is in series with the t-stat. It could be either one.