Q: AC/heater not blowing on high.

Having your AC and Heater make a humming noise while running on high can be an annoying occurrence while you are trying to enjoy driving your truck. Since the problem is persisting after replacing the blower motor resistor, there are two possible problems. You may have a faulty new part or the problem lies not in the resistor but in the blower motor itself.

If you were able to replace the resistor yourself, then you may feel comfortable inspecting the blower motor as well. Without the proper tools and experience it will be difficult to diagnose the problem if it is electrical, but with dropping down the blower motor it may reveal a problem you can see visually. The blower motor is exposed to the outside air and, despite having a filter that strains out pollen and debris, it is still possible that something may be obstructing it from blowing air on the highest setting. Rather than take a guess and possibly waste money however, I highly recommend enlisting the help of a certified mechanic. With their aid you can get the proper diagnosis and get your blower motor operating normal again.