Abstract: Retrofit systems are provided to convert existing automated vehicle washing systems from using conventional car wash chemicals to highly concentrated chemicals. The retrofit systems enable a car wash operator to control the feed volume of concentrated chemicals that are fed to a spray arch where the chemicals are mixed with water before being sprayed on a vehicle. The system provided enables the operators of existing car washes to convert from conventional chemicals to highly concentrated chemicals without purchasing an excessive amount of new equipment or carrying out extensive modifications of existing equipment. A novel feature of the present invention includes the use of a concentrate feed control block for controlling the volume of highly concentrated chemicals delivered to the spray arch of the car wash where the chemical is diluted with water before being applied to a vehicle.