True gdm12 evap fan runs all the time evev with the compressor off wiring seems not to have been touched

Clicking like this is usually a problem with the compressor start device. They are prone to failing and the overload protector is cycling to hopefully protect the compressor from burning out. If the start device is a solid state device if you remove it from the compressor it should not rattle. If it does it is bad and will need to be replaced. Installing a new strat device should get it back up and running.

Give the evaporator a chance to get cold, then check you've got power to the fan, via the evaporator thermistor and door switch

low refrigerant, leak, evap fan inop, thermostat inop.

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Look to the fan delay/defrost terminator that is located inside to the evap. It is usually attached to the evap coil. check there first.

most freezers have 2 controls. 1 is a defrost terminator and the other is a fan delay. the delay and the defrost terminator can sometimes be a "2 in 1" type switch. you would have to study the wiring diagram. The delay will not let the fans come on untill the evap reaches a preset temperature. take another look at the diagram. It may be that the evap is not getting cold enough. you may have a refrigeration issue.

In most cases, there is a device located in or on the evap that senses the temp of the evap. This can be a defrost terminator/fan delay. Sometimes they are separate devices and sometimes they are a 2 in 1 device. If the evap does not get cold enough, the fans will not come on. Usually about +20 degree F. It is to prevent circulating warm air after a defrost and to keep from overloading the compressor after a defrost as heat is generated by electric elements. I would look to see if the defrost terminator / fan delay has malfunctioned, then I would check the refrigeration system performance.

http://www.truemfg.com/pdf/InstallManuals/T-SERIES/t_series_english.pdf
Go to this web site and look in the manual on page 15. Check "Compressor runs but will not refrigerate". Gives some suggestions.
Now, inside the evap, usually strapped or clipped to the coil "U" turn on the end of the coil, is a Klixon device. This device comes in many different configurations. There may be 1 or 2 of these. One is a defrost termination switch. When evap gets hot enough so no frost is present, it terminates the defrost cycle. The other is a fan delay. It comes on when the coil temp gets to about 20 degrees. This prevents circulating warm air from defrost cycle. Now if there is only one device, it can be 2 in 1. That is, a defrost terminator/ fan delay. Will most likely have 3 wires going to it where as the 2 separate ones will only have 2 wires to each one. Now, either this fan delay is not working correctly or the coil is not getting cold enough. When it gets cold enough, it turns on the evap fans. This is most likely where your problem lays. Check it out.

Freezers have a sensor that is referred to as a "Fan Delay/Defrost Terminator". It senses the temp during the defrost cycle. Usually, when the evap temp reaches about 50 degrees, there should not be any frost or ice on it. This device terminates the defrost cycle. It also keeps the fans off so warm air is not circulated. When the evap gets to about 20 degress or so, the sensor switches on the evap fans. If the fans are not coming on, either the sensor is bad or the evap is not reaching the proper temp to cause the sensor to turn on the fans.

Hope is helps to clear up some things and point you in a direction as to what might be going on.

Most all commercial freezers have some sort of fan delay/ defrost termination device. Commonly called a "Klixon" (pronounced clicks-on). It is a device that is attached to the evap. It's function is to terminate the defrost cycle when the evap reaches a certain temp, say about 50 degrees or so, to ensure there is no build up of frost/ ice on the evap. It then allows the compressor to run, and cool the evap down to a reasonable temp., say about 20 degrees, and then let the evap fan come on. It prevents overloading the compressor during a high temp condition, and it also prevents circulating warm air left from the defrost cycle. I believe this device is most likely your problem. With no air circulating, the box will no cool down.. I have seen them burn and/or slhort internally. They can come apart. too. I would look here for that problem. the True manufacturing website does not give alot of info on this piece of equipment, such as a wiring diagram but manuals are available.
Check this out and let me know how it comes out.

This sounds like a stuck relay to me. I have seen this problem before. The defrost clock kills power to the compressor relay coil during defrost. If the contacts in the relay are welded together the compressor runs while unit is trying to defrost. On newer units this relay is mounted in base of unit on the side or back of the electrical box near center bottom of unit. The compressor relay is a small rectangular box with 4 wires attached. It can be replaced with a single pole 20 amp contactor with a 120 volt coil/ or 240 volt. Check the units name plate voltage rating and ratings on old relay! ;)