Ugly_old_Poo_kid said:You'll need to tip the sled, to get the bubble to move to the front where it can be worked out.
Best would be lifting the front while the back stays on the ground, but without a lift that's tough, so tipping it onto it's left side can also help, but not quite as effectively.
You need to work it around and keep topping off the reservoir until you can run it and feel the coolers warming up.
It will probably take several tries to get it all out. It may even work well once, then after shutting it off, there may be enough of a bubble to interfere with circulation again, so you'll have to bleed it again.