Blower motor speeds changes with gear select

[BigRed97]

So I've noticed this since I got the JT but now that it's colder out it's bugging me..

Can any one else hear and/or feel the blower motor speed up when you shift into park and neutral and slow down when going into reverse or drive???...

It's both audible and noticable in air flow. Happens EVERY TIME.

It's not a lot of change but it's there

Any ideas?

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[ShadowsPapa]

So I've noticed this since I got the JT but now that it's colder out it's bugging me..

Can any one else hear and/or feel the blower motor speed up when you shift into park and neutral and slow down when going into reverse or drive???...

It's both audible and noticable in air flow. Happens EVERY TIME.

It's not a lot of change but it's there

Any ideas?

There's a whole lot going on electrically on these things. Depending on the alternator size, fan wattage (max tow cooling fans are big electric users) - you are changing RPM of the engine so changing the speed of the alternator - there's a lot of what-ifs and maybes, but without hearing it my response would be anything from normal to maybe you have a faulty connection dropping voltage and causing it.
I don't know what the idle amperage output is on these alternators but it drops like a rock on many.... and any load at all can cause an audible or visible change in things. Are the headlights on, for example - foot on the brake pedal - you then have brake lights on, so many variables without hearing it.

 

[BigRed97]

It's a max tow so it's got the bigger fan motor and the bigger alternator...

My first thought was an added electrical load but I wasn't quite sure how to explain it... And it does it no matter what configuration the truck is in.. lights on/off, cold/hot etc ...( I have a hard time buying the trans alone has that much electrical load to it)

And speed of the blower doesn't seem to matter either (althought it's obviously more audibly noticeable on higher speeds)

It'smore of an annoyance than anything.

If anyone wants to check there's to see if it's normal or not that would be great lol

 

[ShadowsPapa]

It's a max tow so it's got the bigger fan motor and the bigger alternator...

My first thought was an added electrical load but I wasn't quite sure how to explain it... And it does it no matter what configuration the truck is in.. lights on/off, cold/hot etc ...( I have a hard time buying the trans alone has that much electrical load to it)

And speed of the blower doesn't seem to matter either (althought it's obviously more audibly noticeable on higher speeds)

It'smore of an annoyance than anything.

If anyone wants to check there's to see if it's normal or not that would be great lol

Not the electrical load of the transmission - but the fact the engine speed may change between neutral or park and being in gear. I haven't paid attention to mine - only been in it and driven it once so not sure if the system keeps the engine speed exactly the same in gear or not. Used to be when you went into gear the idle speed dropped a tad. The transmission itself wouldn't have enough electric draw to do it. That would be very small.
Do certain lights on these operate when in gear but not when in park/neutral? I've not paid attention! Guess I could get in mine and fire it up and turn the heater blower on high and see what happens. I rarely run them on high - don't like the noise and with hearing aids it's really annoying because that sort of sound is picked up before anything else.

 

[Hootbro]

You have the "Auto" climate control? Mine does the same thing and pretty sure it is the rationale of the defrost system.

 

[ShadowsPapa]

You have the "Auto" climate control? Mine does the same thing and pretty sure it is the rationale of the defrost system.

AHA - I'd forgot about that. I'll have to see how mine behaves.
Defrost cycles the AC even in cold weather. At least it used to in earlier vehicles.

 

[Hootbro]

I picked my Rubicon up early this summer and ran the HVAC in manual mode. When fall hit and things cooled down, I switched to auto mode and notice the higher fan speed when I first started up in the morning when it was colder outside. Once I shifted to drive, it went down in fan speed.

 

[ShadowsPapa]

I picked my Rubicon up early this summer and ran the HVAC in manual mode. When fall hit and things cooled down, I switched to auto mode and notice the higher fan speed when I first started up in the morning when it was colder outside. Once I shifted to drive, it went down in fan speed.

That's the opposite of how my Chevy was - the fan was on low when I first started it and then ramped up as the engine temperature increased - otherwise it would have blown cold air on you. It was designed to keep from freezing you out until the air was warm enough coming through the heater core. I used to run it on auto and my wife reached over and turned the fan on high and froze me out until it warmed up. I said LEAVE it on auto.... it knows what it's doing LOL
These appear to be the opposite by your description.

 

[Hootbro]

.................
These appear to be the opposite by your description.

In a way, it makes sense. In Auto Mode, and in a non drive gear like Park or Neutral, you want the blower fan running higher for the evaporator coil for the defrost to remove humidity and wick away and either remove or prevent the windows from fogging up. Once in a drive gear, the methodology changes in that the evaporator coil now has outside ram air coming across its coils and use of the fan speed is less needed. That is why they do not recommend running the recirculate function in pure defrost mode and in some electronic climate control systems, it will kick you out of recirculate mode if in defrost mode.

 

[BigRed97]

Mine has manual climate controls

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