A controller of an HVAC system is communicatively coupled to a liquid-side sensor and a shutoff switch. The controller stores measurements of a liquid-side property over an initial period of time. The controller detects that the shutoff switch is tripped at a first time stamp corresponding to an end of the initial period of time. The controller accesses the measurements of the liquid-side property. The controller determines, based on the measurements of the liquid-side property, that the liquid-side property has a decreasing trend. In response to determining that the liquid-side property has the decreasing trend, a malfunction of a blower of the system is determined to have caused the shutoff switch to trip.