As the second-to-last step in the body-off restauration of my M997 ambulance, today I started the M997 cabin heater for the first time (the last step will be to get the A/C running, hopefully).
Everything went fine with the heater, apart from some excessive smoke due to the long pre-ignition phase with some unburned diesel collecting in the heater.
With the temperatures today being just above freezing, the heat coming from the running heater was pretty welcome.
I took a litte video of the test. The first part was filmed inside the M997 A/C-heater compartment. Ignition starts at 0:45. After the heater ignited, the ventilator switches to higher revs, and from 1:20 on, you´ll see that excessive smoke.