The A/C also forces the fan on low. I have the B&M SuperCooler. I'll put the A/C on if I see the trans temp go over 220 degrees (have an Aeroforce gauge set to alert me). Never really gets too hot just crawling, but it will if there is extensive climbing. Putting the A/C on drops the trans and engine temps down in no time. The fan also comes on with the engine temp is over 215 degrees. Don't know what temp the trans temp needs to be to force the fan on, but I know it's greater than 220 degrees since I monitor it pretty closely.