Blower motor hum on 4th speed.
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Blower motor hum on 4th speed.
Got a 2011 XLT. Manual HVAC. Fan speed control for first 3 speeds is ok. I"ll put it on 4th and I'll get a loud hum and no fan. Go back to any other and its ok. Last year I replaced resister, motorcraft one, because I lost first 3. Worked fine till now. On very rare occasions it might work. But if I go back to 1 2 or 3 then 4 it's back to humming and no fan.
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From: St. Louis (Out in the woods)
Probably the HVAC module itself, that's the module with all the ***** on it.
In the highest speed position, the blower speed switch simply bypasses the resistor (which eliminates it as a suspect) and is supposed to connect the low side of the blower motor directly to ground. Now, it *might* be a faulty ground for this portion of the circuit but I'd expect there to be other weird electrical problems to also be present, especially when high speed blower operation is attempted. An inspection of the ground that are behind the driver's side kick panel would be a good idea to do first since the HVAC module is quite expensive.
In the highest speed position, the blower speed switch simply bypasses the resistor (which eliminates it as a suspect) and is supposed to connect the low side of the blower motor directly to ground. Now, it *might* be a faulty ground for this portion of the circuit but I'd expect there to be other weird electrical problems to also be present, especially when high speed blower operation is attempted. An inspection of the ground that are behind the driver's side kick panel would be a good idea to do first since the HVAC module is quite expensive.
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Thank you for the reply.
I'm no electrical wiz kid but that makes sense regarding module. What is weird in most cases if the truck has been off for awhile, 4 speed will work. I can go back to any speed then to 4th and it works and no humming sound. Short time after back to problem. I never use 4th but I'm having my ac recharged in a couple of days. I believe they go to highest speed. Not sure if it can be done in 3rd. Regarding bad ground I don't have any other problems but I"ll take a look.
Couple of years ago I changed the blend door motor and had the whole face plate off to get to motor. So if I need to change it, its not bad.
Update:: I noticed if the blower motor goes unused like overnight, it will run on high when I'll put it on after starting. This morning and last few its been doing it. Sitting all day at work then starting it, the same. If i run the fan for a bit then go to high, 4th, it then will cut off and hum. Would it be the motor?
I'm no electrical wiz kid but that makes sense regarding module. What is weird in most cases if the truck has been off for awhile, 4 speed will work. I can go back to any speed then to 4th and it works and no humming sound. Short time after back to problem. I never use 4th but I'm having my ac recharged in a couple of days. I believe they go to highest speed. Not sure if it can be done in 3rd. Regarding bad ground I don't have any other problems but I"ll take a look.
Couple of years ago I changed the blend door motor and had the whole face plate off to get to motor. So if I need to change it, its not bad.
Update:: I noticed if the blower motor goes unused like overnight, it will run on high when I'll put it on after starting. This morning and last few its been doing it. Sitting all day at work then starting it, the same. If i run the fan for a bit then go to high, 4th, it then will cut off and hum. Would it be the motor?
Last edited by Horsepuller; Jun 4, 2024 at 07:46 AM.
