The present application reveals a device for verifying a proper heat exchange and overall performance of an air-conditioning system. The device includes means for measuring a temperature differential between ambient and vent temperatures of the air-conditioning system, where the means comprises at least two remote probes for measuring the ambient and vent temperatures, or a remote ambient probe for measuring ambient temperatures and an integral vent probe for measuring vent temperatures; and means for analyzing the temperature differential in order to give an indication of performance of the air-conditioning system.