Blower Speed Question

[MAS Tequila]

This is kind of a strange one.

My AC is working as good as a 17 year old system can be expected to in 90+ heat in south Florida.

I have replaced the blower motor about a year ago.

The blower is on the highest speed 99% of the time and there is no issue.

Here is the question: Sometimes the blower will speed up, almost say 15-20% faster, a really noticeable difference for a few minutes.

Does anyone have any idea why it is speeding up?

Is something going bad and not letting it function properly?

It's a loaded Mountaineer, so it does have the climate control not the manual controls.

I'm just wondering if maybe there's something more I can get out of it in the Hellish heat, or something to fix before it goes out while it's 140 degrees inside one afternoon.

MT

 

[bobflood]

Actually, the speed that you are running "99%" of the time is probably not the highest speed. You are just seeing the highest speed occasionally. This sounds normal to me - the EATC has a solid state blower motor speed control instead of discrete resistor values to control the blower motor.

 

[crunchie_frog]

Can you run the fan at all speeds low - high? The blower motor resistor (solid state blower motor speed control) mentioned above is a very, very common failure. It usually presents itself as the motor just running at its highest speed.

 

[koda2000]

Are you sure the motor is actually running faster, or could it be the it sounds louder and seems to blow harder when you EATC controls are set to MAX A/C? When on this setting the outside air door is closed and 100% of the air is coming out the panel vents. This makes it sound/feel like it's blowing harder.

If this is not the case, I agree something may be going on with your blower motor module. Fairly common failure, but usually will just blow on the highest speed. Some here have managed to take the module apart, clean it and re-solder the circuit board or replace electrical components if you're up for that. There's also a test procedure for the EATC controls, though I don't remember what it is (hold certain buttons down for so many seconds and get codes) but you can Google it.

 

[MAS Tequila]

It runs on all speeds.

I have it on max 99% of the time.

And every now and the it will pick up some speed.

MT

 

[SWIGIN]

This is not the easiest thing to do I'm sure but if you ran a hot wire to the motor and triggered it with a rocker/toggle switch it would be on 100% high.

Full 12 volts to the motor is all the faster it is made to run so you could hot wire it to be sure.

 

[koda2000]

It runs on all speeds.

I have it on max 99% of the time.

And every now and the it will pick up some speed.

MT

Bad connection or poor ground maybe?

 

[J_C]

The fan only running at highest speed is a fault primarily seen on the manual climate control resistor pack. When the EATC transistor module (which replaces the resistor module on the manual version) fails, it could do that, always run the fan even if the head unit isn't trying to power the fan at all, but more likely the fan wouldn't work at all.

Although you replaced the fan not too long ago, sometimes a fan bearing can get some play where it'll run up to a certain temperature then the change in tolerance from metal expansion and bearing lube thinning can change RPM, or (not knowing the intricate details of how the EATC head unit works) it could even be putting the fan at a higher power level while the A/C compressor is on.

One thing you can do if you can consistently replicate the fan blowing harder is measure voltage getting to the fan with a multimeter to see if it is fluctuating much. When it blows faster the voltage could actually drop a little if this is a fan fault, but if the fan blows faster due to a voltage rise then it indicates the heat unit is telling it to do this and since you report a full range of blower speeds otherwise, it would seem to be working as it should.

I would NOT wire 12V direct to the motor with a toggle switch. If the voltage wired to the motor like this is higher than the output from the transistor pack, it could damage the transistor pack. You could put a diode in series on the positive power lead from the transistor pack to the fan protect it, but that drops ~ 0.7V which would limit the output from the transistor pack to a lower peak speed. In other words if you want to direct wire 12V to the fan and run it at 100% always, I would unplug the transistor pack from the circuit. I do not know if the EATC head (dash) unit would generate an error message by doing this. If so then you'd need the diode in series, one rated for more than the max fan current, I'm guessing a 30A diode would be a safe value but it would need a heatsink, so mounted on a substantial piece of metal to 'sink away heat, with some heatsink grease. I'd expect the fan lifespan to be a lot shorter always running at 100% but sweating bullets is worse than buying a fan more often.

EDIT: I overlooked the obvious. You could use a toggle switch if it is dual throw, such that one throw is from the transistor module and the other throw is from 12V direct from battery (but a fuse added), such that when one is selected the other is not electrically connected, with no diode needed, but I still don't know if it would cause an error message on the dash head unit.

 

[koda2000]

The fan only running at highest speed is a fault primarily seen on the manual climate control resistor pack. When the EATC transistor module (which replaces the resistor module on the manual version) fails, it could do that, always run the fan even if the head unit isn't trying to power the fan at all, but more likely the fan wouldn't work at all.

Although you replaced the fan not too long ago, sometimes a fan bearing can get some play where it'll run up to a certain temperature then the change in tolerance from metal expansion and bearing lube thinning can change RPM, or (not knowing the intricate details of how the EATC head unit works) it could even be putting the fan at a higher power level while the A/C compressor is on.

One thing you can do if you can consistently replicate the fan blowing harder is measure voltage getting to the fan with a multimeter to see if it is fluctuating much. When it blows faster the voltage could actually drop a little if this is a fan fault, but if the fan blows faster due to a voltage rise then it indicates the heat unit is telling it to do this and since you report a full range of blower speeds otherwise, it would seem to be working as it should.

I would NOT wire 12V direct to the motor with a toggle switch. If the voltage wired to the motor like this is higher than the output from the transistor pack, it could damage the transistor pack. You could put a diode in series on the positive power lead from the transistor pack to the fan protect it, but that drops ~ 0.7V which would limit the output from the transistor pack to a lower peak speed. In other words if you want to direct wire 12V to the fan and run it at 100% always, I would unplug the transistor pack from the circuit. I do not know if the EATC head (dash) unit would generate an error message by doing this. If so then you'd need the diode in series, one rated for more than the max fan current, I'm guessing a 30A diode would be a safe value but it would need a heatsink, so mounted on a substantial piece of metal to 'sink away heat, with some heatsink grease. I'd expect the fan lifespan to be a lot shorter always running at 100% but sweating bullets is worse than buying a fan more often.

I agree that it could be the motor bearings. I had a house fan that would do this. A few drops of oil on the bearings would get it running at normal speed again.

 

[MAS Tequila]

It has done this with three different fans installed, so I seriously doubt that all three had bad bearings.

I changed the last one because it started making noise. Once I got it out I saw that a piece of a packaging card had slipped through the cage and it was doing the bicycle spoke thing on the hamster cage.

I put the new one in anyway.

MT