First post here. Thought I would repay my findings as this group helped me narrow down and solve my problem. 1999 ES300 had the fans running all the time problem, after reading almost everypost in this forum and others on the net I found the problem and fixed it for free. As we all know both fans should run when the AC is on, and the selected temp low enough to make the compressor turn on. When AC is off no fans should run. Mine ran all the time when vehicle was running or the key turned to ACC. I tested all relays and connectors were good. I read one post inparticular that made the most sense regarding the AC pressure switch and how it commands the fans. After googling and reading enough sites I found a diagram regarding its location, found it on my car,and low and behold I found one of the 4 wires coming out out the plug was broken. This defaults the system into a safety mode of protecting against overheating by making the fans run continuously. After soldering the one wire everything worked like a dream. See the the pics. I thought about how this system works and and concluded that my situation pointed to the AC pressure switch or its connectivity. I was lucky enough after finding it that the plastic shroud around the 4 wires on the connector was somewhat ripped enough to expose the one broken wire for me to see. If the break was further down the line I might never would have found it.. The switch is connected to the receiver dryer just in front of the condenser in front of the radiator by the Passenger side headlight. Easy access.
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