Evap fan will not come on,jumped out the fan control fan comes on

Check to see if the door switch is stuck open

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.

start simple. be sure that the condenser coil is clean. you should be able to see all the way thru the fins. verify that the evap fans and the condenser fans run. make sure nothing blocks air flow inside the conditioned space and around the condenser coil and compressor.
Let me know if we need to go further.

a coil covered in ice is one of two things
your defrost is not working or your circ fan is not working
make sure the fan inside is free and spinning
the make sure your defrost timer is operational
the bev airs are usually right in front behind the toe kick
short of that ohm out your heater to ensure its working

It runs when the compressor runs except when it's in the defrost cycle. If you have an electronic control instead of a defrost timer the control could be the problem since it runs the fans. You can test the evaporator fan. See how here> How to check everything
http://www.acmehowto.com/howto/appliance/refrigerator/refrigerator.php

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.

If this is a commercial unit, you're too low on refrigerant (freon). Freezer should be about a minus 10 degrees for the evap and high side is ambient converted to a psi for the type of refrigerant that is in the system plus 25-30 psi.
The evap fans will not come on because the evap is not cold enough.
Hope this helps and good luck.

If this is a Bev-Air, don't think the door switch will control the fan. At the evap, there is a temp sensor called a fan delay. When unit goes into defrost mode, this warms up. Some also serve a dual purpose. It will terminate the defrost cycle at a certain temp., say 51 degrees or so, at the evap. Anyway, when unit comes out of defrost, it keeps the fan off so it allows the evap to cool quicker and to prevent circulating warm air. This could be your problem. Not a hard fix but they can be a pain sometimes. Outside chance that the unit is low on refrigerant (freon). This will not let the evap get cold enough to trip the sensor back into position to turn the fan on. Good Luck. Restaurant Parts and More carry alot of Bev-Air stuff. 1-888-814-1110. Ask for Rick