Shocker73 Posted August 1, 2014 Share Posted August 1, 2014 Ok guys, I've posted this elsewhere with no luck so far. Maybe someone on here has had this problem and knows a fix.Original:2014 Mack CHU Pinnacle w/mp8. Any idea what would cause the fan to stay on continuously? Just started today loaded, empty, sitting still with a/c on or off. This trucks fan runs in high stage more than any other truck I've ever driven but never in high stage all day. Any ideas?Today Update:The truck has been at the dealership all week. The computer told them it was the clutch fan so they replaced it. Still runs continuously on high. They ran several computer test on all sensors and electrical and can't find the problem. The last thing they tried was hooking up another ECM (I think) but still no change. This is a Mack service center so I'm sure they check the most probable causes maybe its something unusual that they wouldn't think of. Have any of you had or heard of this problem, if so please give me some insight.Thanks Quote Link to comment https://www.bigmacktrucks.com/topic/36530-fan-runs-on-high-continously/ Share on other sites More sharing options...
wheeler73 Posted August 1, 2014 Share Posted August 1, 2014 Have them monitor the a/c fan switch also called the a/c high pressure switch that the computer monitors. If it is stuck in the on position it will cause the fan to stay engaged. Also if the a/c system is equipped with APADS it could be in that also. I see the above alot. Quote Link to comment https://www.bigmacktrucks.com/topic/36530-fan-runs-on-high-continously/#findComment-254638 Share on other sites More sharing options...
turckster Posted August 4, 2014 Share Posted August 4, 2014 With a diagnostic computer hooked up (PTT 2), the dealer should be able to run a test to see if the fan is requested on and what is requesting it. If nothing is requesting fan engagement then I would focus on the engine harness-make sure the fan harness is pinned correctly. Make sure one of the harness pins have not backed off inside the connector, wire inside the loom have not rubbed together and so on. What type of fan do you have? Air, viscous electronic? With the air fan I would make sure there is air to the fan and solenoid. With the Borg/Warner electronic viscous fan if there is a loss of voltage the fan will stay engaged. If the dealer can not figure out why the fan will not disengage then they should get Mack technical support involved. Good luck Quote Link to comment https://www.bigmacktrucks.com/topic/36530-fan-runs-on-high-continously/#findComment-254957 Share on other sites More sharing options...
Shocker73 Posted August 5, 2014 Author Share Posted August 5, 2014 Thanks a lot Turkster, it was the harness pins not making a good connection. The head tech was back today and checked back over the others work and found it. Quote Link to comment https://www.bigmacktrucks.com/topic/36530-fan-runs-on-high-continously/#findComment-255030 Share on other sites More sharing options...
Falconfox Posted July 17, 2021 Share Posted July 17, 2021 Hello, I have the same fault in a cxu613 MP8, I think it is an electrical problem, I already checked the pins. Any idea what it could be ?, I would appreciate a lot if you could help me with this information, thank you very much. Quote Link to comment https://www.bigmacktrucks.com/topic/36530-fan-runs-on-high-continously/#findComment-476976 Share on other sites More sharing options...
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