Start when very cold. Cooling fan comes on for a few moments. Then no start. Cooling fans only work with a/c on after cold start. Changed coolant sensor(volvo) and thermostat.
let car run with coolant cap off to check for trapped air and all I got was antifreeze bubbling heavily out of bottle. Going to try again with a/c on so fans run.

 

The fans only come on when the engine is really pretty hot (at least the gas models - diesel could be different, I suppose). My V70 fans were set to come on at 105° C (220°F), for example. If you have a VIDA or other device (like the Torque app with a Bluetooth dongle) you could monitor your actual coolant temperature to see if the coolant is actually hot enough to command the fans on.

 

I wonder if your water pump impellers are shot and no longer circulating the coolant - when was the water pump last changed?