iO HVAC Controls UMM-SP Malfunction Monitor - Pressure SensoriO HVAC Controls UMM SP Malfunction Monitor Pressure Sensor Description The UMM Universal Malfunction Monitor is a solid state, 24 VAC interface module designed to accept a variety of dry contact inputs such as a current sensing relay, static pressure switch, refrigerant pressure sensor or freeze stat. Based on the selected input, the module will trigger a SPDT relay after a selected time of 6 seconds or 6 minutes once the input contacts open. The