REFPROP's equations of state (like ECS, TC, and viscosity models) are complex. If your crack gives a wrong saturation pressure for ammonia at 300K, you have no official forum, no NIST helpdesk, and no patch. Your research or design could be dangerously flawed.
This is the most popular way to access CoolProp's power.
If you require REFPROP for professional or academic accuracy, you should obtain it through official channels: New License (Version 10): Available for $325.00 from the NIST Standard Reference Data Store