[COLOR="Blue"]I checked to see if its defrosting and frost is still forming .[/COLOR]
Frost is forming on the coils so you know the unit is working.
Check that the frost is even across the coils.
If it is very patchy or just is one area (usually where the freon enters the coils), it is an indication of a low freon condition.
Also how long have you waited give it at least 4 hours.

[COLOR="Blue"]The evaporator fan is blowing but not very hard.[/COLOR]
This could be your problem.
The fan may need replacing.

You have replaced the defrost parts but it is not unheard of to get a defective part so I would check them, see below.
Also you may have a bad connection or broken wire between the timer and the defrost heater.

You are sort of loosing me.
After you manually defrost the evaporator coils the freezer should get down to 0 degrees or just above after about 4 hours. It should be OK for a couple days and then the evaporator coils ice/frost over to the point that the fan can no longer pull air through the coils.
If the coils are icing over very quickly check the door seals.

You said the fan did not seem to be blowing properly.
Testing the resistance will not really tell you anything.
The winding could be partially shorted inside or a bearing is shot.
If it does not blow properly I would replace it.

Now for the defrost problem.
First remove the evaporator cover in the freezer so you can see the coils.
Not do not let them de-ice.

Manually force a defrost cycle by turning the defrost timer cam (Item in Section ) 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 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.

(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.