Splitter stuck

Pull the supply line off the compressor and fill it with airline antifreeze. That way it will thaw out the whole system if you can't get it in a warm shop.
If it's really iced up,you will have to get under the truck and start heating valves and fittings with a torch.
Just be careful of the plastic.

 

You need to find the supply line and find where the blockage is. Pour some room temp water OVER the frozen valve and it should thaw. High idle like 1200 rpm and cycling through your air for 10 minutes might provide enough heat to thaw it out as well

 

If pressure puts it into the high range, find the vent. Might be iced up/blocked. Remove, and it should work. Thaw it out inside the cab and then replace it once cleaned out & dry to keep crap from entering in through the fitting's hole.

 

I wonder if your compressor is tired?

 

May need new air dryer also.

 

Vent is at bottom of dryer usually. The thing that makes wooooose sound when it reaches 120 psi.