Defrost problem

hi all
i had defrost problem with my refrigrator.I replaced every new part which can cause defrost problem.I replaced heater,thermostat,mainboard thermister. But i am not sure if defrost cycle is working or not.Is there any way that i can test it.Can sombody help me or i have to monitor the coils for 2-3 weeks to check if there is any ice buildup.Waiting for any response.

What is a mainboard thermister??

If you replaced everything, you are probably going to be ok, I would monitor the freezer temperature to check.

i replaced the part one by one, not at the same time.I changed heater first then thermostat,then motherboard and when the problem was not solved then i replaced thermister.If thermister was bad or short, can it short the other part like mainboard or motor. Because i know heater is working good because i jump start it.But i never saw the heater on during defrost cycle since i changed the thermister two days back.Can we see the heater glowing while defrosting.Do you know how many times this model defrost in 24hrs.

If the freezer temperatures are ok, you are probably ok, in this hot, humid weather, it would have frozen up by now.

you can see ice on middle coils but top two and bottom two coils are very little ice.Temp in the freezer is ok.Everything in the freezer is frozen right now.