We have a 2010 Prostar that has problems with the airflow coming out the vents while going down the highway. He will be going down the highway and the airflow will reduce to almost nothing. When the driver comes to a stop, it will start back up again. We have verified function of all of the actuators and ductwork.The blower motor also doesn't reduce speed. Anybody have any tips/experience with this problem? VIN 3HSCUAPR4AN272126
No experience with that exact problem on that exact truck, but I have few suggestion or questions to ask yourself. 1. Could the module on the blower motor be going out when it gets hot? 2. You said heater, but could the unit also be in defrost mode and the evaporator is freezing up from the A/C clutch staying on due to faulty inlet and outlet temperature readings. You will need to use dimaond logic builder to look at those 2 temperatures. If the evaporator freezes it will restrict air flow. In the winter time there is a larger delta between outside ambient temperature to condensor temperature, so the system can pull heat out of the system much quicker going down the highway versus when the unit stops.
Freightliners use to have that problem all the time with the Blend air system, winter or summer. Driver complaint no air flow. The HVAC relay would stick close and the system could not cycle the A/C clutch to prevent freeze up. You could indentify this by turning on the ignition switch and the compressor clutch would be engaged. On a blend air system the clutch should not be enaged with just key on, a parameter that needs to be seen by the AC module is engine rpm above 500 rpm for 15 seconds.
I belive you can do this same check on a ProStar, the A/C clutch output is direct from the Body Controller to the clutch and it does need to see engine rpm for engagement. Hope this helps with some of the troubleshooting proccess.
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