The Land available for cultivation is decreasing and population is increasing. This necessitates the requirement of adopting scientific methods for achieving maximum production. Maximum yield from crops can be achieved by proving required quantity of nutrients and water and also the desired level of microclimate. Microclimate modification is possible in greenhouses and this is the advantage of greenhouse cultivation compared to open field cultivation. Greenhouse cultivation requires microclimate management as well as application of water and nutrients to plants daily. This requires labour and this cost can be reduced by adopting automation systems. This paper presents a performance study of a locally developed low cost automation system on greenhouse cooling. Temperature inside the greenhouse is to be reduced in summer in Kerala which falls under humid tropical climate. The automation system installed in one greenhouse and temperature recorded at hourly intervals. Temperature measurements were taken from another greenhouse which is manually controlled. Saniya variety of salad cucumber was cultivated in both the greenhouses. Temperature data and crop data from both the greenhouses collected and compared. Performance of the automation system was good in controlling the greenhouses temperature. Yield obtained from greenhouse operated by automation system was higher compared to other.