A direct exchange heating/cooling system with at least one of a reduced compressor size, with a 500 psi high pressure cut-off switch, with a 98% efficient oil separator, with extra oil, operating at a higher pressure than an R-22 system, with receiver design parameters for efficiency and fox capacity, with geothermal heat exchange line set design parameters, with special heating/cooling expansion device sizing and design, with a specially sized air handler, and with a vapor line pre-heater.