Not sure what you meant on you compression release operation. I have a L185 which is smaller but similar to your L235.
On mine there is a cable like a choke on the dash. Pushed in there is compression (compression relief is off). Pulled out there is NOT compression (pressure relief is on).
I live in a warm climate and still have to use the glow plugs to get it to start in a reaonably short amount of cranking.
Just to cover the basics (which I imagine that you already know). The key should be turned one position to the right to have electrical power. The starter knob should be rotated and held in the CCW position for a few seconds (30?) to warm the glow plugs and then the starter knob rotated to the CW to engage the starter motor.
If the compression relief cable is out it will turn much faster (10 to 20% I would guess) than when the compression relief cable is pushed in.
I do not start mine using the compression relief although I have done it a few times. Pull out cable, crank for a few seconds (2-3?) to get speed and push cable back in.
Sorry if these seem obvious but I am just making sure you have the steps correctly outlined.
I am no expert on deisels but they operate fairly similar to gas - you have to have compression, fuel and air. The only thing is the fuel injection is timed to the engine as mentioned in another reply. If you can't get it to start then I would try to eliminate problems with the air intake since that is the easiest, then clean out the fuel system and replace the filter and bleed the lines out. Then insure your glow plugs are working properly and then go to the compression tests (last since I would not have the equipment to test it).
Have you checked the fuel filter, checked for water or algae in the tank or fuel lines. Used any additive in the fuel that could affect it? Have you checked the air filter - is it choked off and no air into engine possible?