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Replacement parts for MAYTAG PBF2255HEW Ref - Bottom Mounts | AppliancePartsPros.com

I could not find a tech sheet for this unit. Look under the unit in compressor area for it. Perhaps the following will give the procedure to force a defrost cycle, see Page 38 in the manual.
http://www.servicematters.com/maytag_library/docs/16025629.pdf

Could be any one of the items you mentioned.
Note that you do not have a defrost timer the defrost is controlled from the board.

First remove the evaporator cover in the freezer so you can see the coils.
Not do not let them de-ice.
If they are heavily iced/frosted over you have a defrost problem.

If yes.
Manually force a defrost cycle by turning the defrost timer cam till the fans and compressor turn off.
Now check the defrost heater to see if it is on.
Be careful you do not want to burn your fingers.
If the heater is on then the timer needs replacing, re: it is probably stalling during it's rotation so is never getting into a defrost cycle.

If not on.
Unplug the unit.
Remove the wire for one side of the heating element from the wiring and measure it for continuity, usually around 20 ohms or so.

If the heater is OK
Remove one wire to the defrost thermostat and measure it, should be 0 ohms when frozen. Note that it opens just above freezing so must be frozen to check it. Also inspect it, if it is bulged at all replace it even if it measures OK.

If both the above are OK then odds are the defrost contacts are toast.
Best way to test this is a live test to see if you have 120 volts across the heater/defrost thermostat combo.

Here are a couple good sites with additional info
http://www.applianceaid.com/frig.html
Refrigerator Repair Guide: How To Fix a Refrigerator - ACME HOW TO.com

If you do not own a meter, I would suggest you purchase a one. You can get a decent digital multimeter for under $20.00. You do not need fancy though it is nice if the leads are a couple feet long.
If it saves ordering one unnecessary part it has paid for itself and you end up owning a useful tool.
Most places will not let you return electrical parts so if you order it, you own it.
A couple things to watch when measuring ohms and continuity
1. Always remove power from the machine otherwise you could blow your meter.
2. Always disconnect at least one side of any device you are checking. This eliminates the possibility of measuring an alternate/parallel circuit path.
3. When checking for closed contacts and continuity use the lowest scale (Usually 200 ohms). Then try higher scales. This scale is 0 to 200 ohms so if the device you are measuring is 300 ohms this scale would show an open circuit which it is not, you are just measuring outside the scale's dynamic range.

There is a good STICKY at the start of this forum about it's use.

[COLOR="Blue"]i READ IN SOME OTHER POSTS THAT IF FORCED DEFROST WORKS ITS NOT A BAD CONTROL BOARD[/COLOR]
No, if you can force a defrost is does not eliminate the board, it does eliminate the heater and defrost thermostat. Perhaps the timer section on the board is not working so that the unit never goes into defrost.

[COLOR="Blue"] kIND OF PRICEY, SHOULD I TRY.[/COLOR]
It is all that is left so I would give it a try.
Since you have doe a lot of troubleshooting, if you order it from AppliancePartsPros and it does not fix your problem, they will let you return it.
see their return policy.