How do you know pcb board is bad for the defrost system

Check for ice / frosting inside the freezer .... If present you probably have a defrost problem.... This causes the freezer coil to ice up and block the air flow ... the causes could be a bad defrost heater , defrost timer, defrost sensors, or control board. Also make sure that the condenser coil is clean. remove ALL dust with a vacuum and a coil brush .the coil is located either on the bottom or on the back side of the unit... You didn't give the Make and model #

Sounds like a defrost problem. Check to see if there is any frost buildup in the back wall of the freezer. If so, it is not defrosting as it should.

• possible causes:

1. bad defrost timer/control board
2. bad defrost heater (in freezer)
3. bad thermo switch in freezer

If you don’t know what these are then unplug the machine and let the ice melt in the freezer overnight with the door open. Then try it the next day, if is cooling fine then you need to have a service person replace one of the above items. 

• if you already checked this and think it is a different problem then let me know, i will help you figure it out. 
  

Mike  


these are the usual suspects.


heater in the back wall of the freezer:



thermal switch also in the back wall of the freezer

There are three parts to all defrost systems.
1. Defrost Heater2. Defrost Timer3. Defrost Thermostat
Without a model number I could not look up a diagram or part numbers. I very seldom see a bad heating element. Most common is a bad defrost timer, second most common is the defrost thermostat.

http://everestref.com/service03.asp?tb_name=Tb_notice6

The board is located under the freezer side of the unit. You can call Sears, as they carry your brand's parts and they will tell you exactly where it is. There are diagrams on the web too. Search for appliance parts. You'll need to enter model number here: www3.sears.com
Fridgidaire refrigerator repair in Orange County, CA

Not very familiar with fisher however I have worked on a few for my friends. Usually the only other two things in a system would be your defrost termination and defrost timer. The more likely and cheaper of the two would be the termination which would be located on the top of the evaporator coils. You can usally visually inspect these and if they are bad they look (popped out). Lastly and most unlikely would be the defrost control. Usually if the control is bad the unit will be completely dead. Let me know if you need more help past the termination.

There is a good chance, if the defrost timer is mechanical, that you can rotate (nudge) the timer to see if it get's going.

Most commercial refrigeration does not use a defrost thermostat, and a lot of it does not use a heater (they use a hot gas bypass valve and pump hot gas through the evaporator, rather than through the condensor.).

Let me know if you need further help.

I'm not familiar with this brand of refrigerator but sounds as if you have a defrost system failure. most refrigs have a defrost timer that you can maually advance into defrost. if you can loate this on the unit then advance into defrost cycle if the heater comes on youll hear a sizzling noise from the ice melting on the heater. this means you have a bad timer. if the heater does not come on then you have a bad heater or defrost termination switch. I tried to find some service info for this mod but was unable to locate anything. good luck peyton

Three things could be the problem. Most likely would be the defrost thermostat which clips onto the evaporator behind the panel in the freezer. 2nd would be the timer or control board (will have one or the other). 3rd would be a bad defrost heater. Alot of times the def. therm. will show obvious sign of being bad by the cap on top popped open. You can check resistance on the heater. Any resistance at all on the heater means it is good. If it has a standard timer turn it clockwise until it clicks. This is putting it into defrost. If the heater comes on the timer is bad. If it has a control board you would unplug the unit then unplug the power supply to the board and jump line 1 to the wire going to the heater. While unplugged from the board and jumped, plug the freezer back in. If the heater comes on then the board is bad. If you are not sure how to test replace the def. thermostat, which is the cheapest part and see what happens. Note: When conducting the test for the timer or board the def. therm. must be freezing so don't defrost first! Hope this helps.

need a model #.. is this a frost free freezer or a refrigerator ?