Will not start

look at the ignition bypass resistor. It's on the firewall close to the brake master cylinder. It provides full battery voltage while cranking and then runs at reduced voltage the rest of the time. Your ignition switch controls it's operation, so look for a faulty ignition switch too.

Flame sensor next to the burner is eather bad or there is a bad connection at the flame sensor (that's why the kick works)

Leaking intake manifold (vacuum )

! have a 93 Toyota pickup that I started and while it was warming up ,during sub zero weather, it stopped running. Now when I try to start it, it will turn over but will not start. It is getting gas but doesn't seem to be firing.

the alternator has no affect on weather it will start or not... could be a bad crank sensor fairly common on those and definately will not start if it is bad it controls spark

Well the conditions exceed the camera's ability. I suggest that you call Samsung and see if they have the solution. A filter lense may help during the day, but hinder after dark...

Distributor out of time or timing chain.I'am guessing you changed a lot of unnecessary parts and it isn't weather related.

sound like a thermostat

what kind of van?

When the thermostat says AC it means there is no power to the thermostat.