A system and approach for a self-calculating test of a heating, ventilation and air conditioning load. The test may be run upon meeting predetermined conditions. Thermostatic control of the load may be disabled when the load test starts. If a call for heat or cool is made at the thermostat, response to the call may be delayed until the load test is completed, and if AC power is lost during the test, the test may finish and allow detection of the phantom AC detection device with a loss of AC power. If a voltage of a storage capacitor falls below a battery boost threshold, the test may be cancelled to allow the phantom circuit charge the storage capacitor. The system and approach may incorporate load test states that include an initialize state, start test state, get baseline state, test measure state, stabilize measurement state, calculation state, and finalize results state.