2017 Granite GU713 Engine fan stuck on and no A/C

Discussion in 'Mack Forum' started by 40_Watt, Mar 21, 2022.

  1. 40_Watt

    40_Watt Bobtail Member

    My Granite (MP8) truck just recently went to the dealership to have a Box Sensor replaced. When I got it back the air conditioning is not working. I noticed that the engine fan stays on full-time no matter what. coolant level is okay, doesn't run hot, power to AC compressor, AC compressor has good 3.7 ohm resistance on the clutch, refrigerant charge is good. Beating my freaking head against the wall troubleshooting this thing. everything seems to work as it should however, the high and low side of the AC system is not getting cold or warm. blower motor in cab is fine, clean cabin filter and heat exchanger. everything appears to be doing what it's supposed to do however there is no chill occurring on the coolant line. Just stumbled across a couple posts mentioning how the engine fan is associated somehow with the HVAC system. Also someone mentioned something about a DPF system sensor being bad on their truck causing the engine fan to run indefinitely. Caused me to speculate if them changing out my sensor is causing my fan to stay running and in turn causing my AC not to function properly? Any help would be greatly appreciated.
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  3. skallagrime

    skallagrime Road Train Member

    Apr 10, 2012
    You say ac compressor is good and checks out, but 0 heat difference, that tells us 1 of 2 things, either your ac clutch orcompressor arent actually working, or your orifice/expansion valve is stuck full open as if its just an open tube

    Try hot wiring your ac compressor first
  4. kranky1

    kranky1 Road Train Member

    Sep 16, 2015
    Ontario, Canada
    I’m not familiar with the system on that truck, but there are a few things I would check. First the High and Low Pressure Switches on the AC system. Either one of those failing can hold your fan on. In your fuse panel you should find a relay that turns on the AC with Defrost, might look there too. Had a problem with one of those in a KW, long storey, but it burned the truck to the frame rails in the end. The Emissions involvement is a mystery to me, but I would think that’s probably switched from the ECM. Sounds like you’re not getting a signal to the AC clutch for whatever reason. Those 2 switches, and the relay could all be the culprit there. Scary part in it is Emissions System can control fan function and somebody just had their hands in it. I’m assuming it was a NOX sensor you had changed, you should know if your box is up or not without a sensor. Couple things there you can look at anyway.
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