Air Test Geothermal
Use water for you leak test.
You will find the smallest leaks alot easier
You can pressure it up to 60 psi with water easily
I always use water.
Keep in mind air will compress and expand the poly pipe where water won't compress and expand the pipe. And water can be seen where air can't. Water will test the whole system not just the joints and hundreds feet of pipe is hard to check with air.
John Wayne once said "Life is tough and it is even tougher if you are stupid"
Tempstar and Trane Dealer