S60 12.7 Detroit, fan clutch won't engage.

My 99 fan needed air to engage. So when it went bad and started leaking, I had to disconnect air line, crimp it off, and install a bolt to lock the fan into full time operation, till it could be replaced. My 2000 is opposite. When fan goes bad and won’t engage due to leaking air at the hub, I have to disconnect air line, crimp it off, and hub automatically stays engaged, and fan stays on all the time, without air. First step is figure out which type fan you have. Sounds likes the second type mentioned, like my 2000. So I don’t know what the problem is with yours. Only can explain my own experience with both types, on a 99, and my current 2000. They both had the same problem. My 99 it was the harness update I described. I had read about it, and no one knew anything. After about 6 yrs. of constantly asking Dealers and Mechanics. Youngstown Freightliner knew exactly what it was. Sold Me the update kit, even loaned Me a crimp tool. Same problem on my current 2000 model. I’m told it’s the pdmi box described. However recently mine started working properly on its own. My fan hub is currently seeping air. So I don’t know yet if that’s why, or if pdmi box is bad, or maybe I need the same update as my 99. It’s just always been a problem on my Freightliner’s w/ Detroit’s. In fact my 92 WS had the same issue. The bulletin on it was an easy re location of the temp sensing selinoid further from the engine area and installed on the firewall. Are you sure it’s actually engaged, and not just freewheel spinning? They’ll spin at a pretty good pace, while engines running and fans not even engaged.

 

Well, I’ve got a problem I’ve never seen before. My fan needs air to disengage. Take air away, it engages. Normally if it goes bad, starts leaking air, I can crimp the line, and run with it engaged. No need to use bolts to lock it up. It was leaking air, but still working. Now it’s stopped working. Disconnected the air line, and it still won’t engage. Why? Maybe the springs bad, or stuck? Going to try to lock it up using a bolt or 2. Just rebuilt it 2 yrs ago with kit masters kit. Meanwhile I have no a/c cat idle, since it’s not cooling the condensor. Coolant hasn’t got too hot, despite 90 degree weather. Thanks to my new radiator. I can see the large seals blown out. Disappointed in the Kit-masters kit, should have used Hortons new quick kit. It was a 2 day back order at Freightliner, didn’t want to wait. Should have, it was also a bit less money.

 

I put 2 1” 5/16 bolts in it to lock it up. A/C is working! I’m questioning my own memory. I thought this fan engaged when air was Removed, and engaged with air, Opposite of my prior Trucks with Horton fans. I must be wrong. Just glad I could bolt it up. No more kit master kits for me. Pretty sure I did everything right. 2 yr. warranty. That’s how long it lasted, 2 yrs. Not sure if a mini kit cartridge will fix it. Leaking air originally after key was turned off. Then leak was so bad, never even held air. Looks like big o rings blew out the back. Can see where it’s been leaking. New Horton quick kit this time. Comes with new hub, bearings, seals already assembled as a unit.