I recently bought a 2019 T590 skid steer with just over 400 hours on it and so far its been great but recently the heater is only working on low, Ive replaced the fan speed switch and still have only low speed. When I put it on high there's a noise as if it's blowing more air but there is no difference when I put my hand next to a vent. My dealer suggested changing the cabin air filters, he thinks they might be plugged with dirt and snow/water but I wouldn't think that would effect the fan speed. Any thoughts.