My hydraulic cooling fan never turned but it was checked at the factory and woked there. I decided to track down the problem. Since I installed a thermometer into my hydraulic tank, I was able to easily monitor the temperature of the hydraulic oil. By driving around, I raised it to 175 degrees F and the fan still did not come on. I found the thermal relay located in front of the electrical termination box at the rear right of the tractor (see picture below). I checked with a multimeter and there was 12 V on one side of the switch. I aimed a heat gun at the thermal relay but the fan never came on. I could see some sparking as the contacts closed. It looked like there was too much resistance for good contact. Shorting the connection caused the fan to come on. Either the switch was dirty or it was bad. I ran out of time but the next day I stuck my camera down there and took a picture. I wonder why it did not work!!! I removed the switch and measured 400 ohms when holding the contacts down. After cleaning it by sliding a paer twoel repeatedly through the contacts, I measured 0 ohms. I reinstalled the relay and used the heat gun. The fan quickly turned on.