My Refrigerator is an Amana (11 yrs old) model # BB20VPSE (when choosing the correct one, of the two listed on this site, I used the one with the W E on the end.... Manufacturer# is P1321302 W E)

I've read a lot of the posts written on here regarding this problem and have already replaced the defrost timer but the problem still exists. I don't own nor do I understand how to use an Ohmmeter. (This is my first attempt at repairing an appliance rather than calling a repairman, so I am still learning.)

Here's what I have done, so far.... Removed the inside, back wall of the freezer compartment (bottom freezer) and found the defrost heater (also known as a condenser coil, I think, No?) full of ice. Used a hair dryer, and removed the ice (drained into the pan below with no problem). Plugged frig back in and it worked fine for about a day. Then the ice was back and same problem returned. Replaced the defrost timer, used hair dryer to remove ice again and tried again. Another day working fine, but then same problem returned. Was going to attempt to replace the defrost heater, or even the defrost thermostat, but neither part was available... not sure what to do now?

Can you help to find the correct part or would you suggest I call a repairman in now, before I cause any further problems?

Here are your parts
Replacement parts for BB20VPSE models | AppliancePartsPros.com

Below is my blurb on defrost problem troubleshooting/repair

First remove the evaporator cover in the freezer so you can see the coils.
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 (Item 43 in Section 8) 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 (Item 23 in Section 8) 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 timer 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.

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.