I have a True T 23f freezer that I know needs a new defrost timer. My problem is finding the right one. The only numbers I can see on the timer are 8141-00B and 345-00. I can also see it's marked 2hp 40a. I can't find a part diagram for the freezer on line to help determine the timers part number either.

Your freezer compartment will freeze up and not cool properly if the defrost timer does not allow the unit to go into its self defrosting mode to get rid of the ice that serves as an insulator.

Replace the timer.

There is a safety cutout on the evaporator that sometimes goes open circuit, stopping the heater coming on in defrost.If the compressor will not turn off, check the condenser is clean.and the fan working. next check the thermostat hasn't broken. Lastly, check the defrost timer.

As soon as you open the freezer door the temp control is at the upper right of the freezer.

Terminal #3 on time clock is for defrost heater.

Terminal #4 on time clock is for compressor

Are you talking about the fan inside the freezer? If yes, check the following items. The door has a switch that turns the lights off when the door closes, it also turns the fan off when you open the door. If it isn't working right the fan won't come on. There is also a round temperature senser on the coil inside the freezer called a "clickson" that keeps the fan from coming on until the coils are below 20 degrees, it may be bad. If you are low on freon, your coils may not be getting cold enough to trip the clickson. Feel of the small copper line going from the compressor to the coils on the outside of the freezer. It should be almost hot enough to burn your skin if you have enough freon. One other thing to check is the defrost timer. It is a box about 4 inches wide and 8 inches tall with a door on the front of it. Check the connections inside to be sure you are getting power through to the fan. Let me know how it turns out.

http://www.truemfg.com/pdf/InstallManuals/T-SERIES/t_series_english.pdf
this should take you to their site for a manual on your freezer. I has info on the time clock and how to set it.
First, be sure it has the correct power to the unit. I would then check the temperature control. Be sure it is sending power to the compressor unit. If a contactor is used, is the coil on the contactor getting the correct power? Start there and let me know if we need to go further. Good Luck

Is it factory new, never been used? Or are you saying you bought a used one and they replaced it with a "new" used one? I am familiar with True Manufacturing and if it is a new unit you have a one year parts and labor warranty. The dealer you bought it from is the responsible party to fix your problem.

http://www.truemfg.com/pdf/InstallManuals/T-SERIES/t_series_english.pdf
go to this web site for your ops manual. It has details on the timer and some trouble shooting. Try this first. If it does not help. let me know and we can go alittle deeper.
Good Luck

Without knowing if it a freezer or a cooler I will have to guess. Could be caused by a few things. I'll list them in order of the one I think is the most common reason.

Cooler

1. Door gaskets or someone left door open for a time.
2. Thermostat set to low.
3. Low freon
4. expantion valve out of adjustment or needs replaced

Freezer

1. Defrost not working (Will have heaters with a timer)
2. Low on freon or expantion valve

I believe that breaker is actually for door frame heaters. Most true freezers have a resettable breaker for the door perimeter heaters only.