An apparatus for monitoring a heating, ventilation, or air conditioning (HVAC) system includes an indoor unit monitor module electrically connected to a current sensor and first and second refrigerant temperature sensors. The current sensor generates a first current signal based on aggregate current consumed by components of an indoor unit of the HVAC system. The refrigerant temperature sensors generate first and second refrigerant temperature signals, respectively, based on measured temperatures of refrigerant circulating within the HVAC system. The indoor unit monitor module receives, from a secondary monitoring module, a second current signal based on aggregate current consumed by components of an outdoor unit of the HVAC system. The indoor unit monitor module transmits data to a remote server to assess whether a failure has occurred or is likely to occur in the components of the HVAC system. The data is based on the current signals and the refrigerant temperature signals.