AC and Engine REV"S ?

[CraigJones]

Has anyone noticed when the AC or Defrost is on the engine rev's up when taking off from a stop. I know the compressor runs when AC or Defrost is on. Is the electric fan kicking on to make this noise ?

 

[David Muench]

Are the engine rpms actually higher than normal, or are you just hearing the fan because the fan has electronically locked up?



Mine does it all the time, and for good reason. Once I am moving fast enough for good airflow through the radiator and condenser, the electric clutch unlocks and the noise stops.



I think it's cool, I enjoy scaring pedestrians with it.

 

[CraigJones]

The rpm's don't go up. I just wanted to make sure that it is the fan.

 

[TheWolf]

I actually noticed the same thing today. Only had the truck 2 weeks and only 2nd time with the ac on(hasn't even been into the 80's until this week) I didn't know what was going on? It sounded like the fan was running with the engine rpm's. I noticed it when I was accelerating from a stop. Didn't do it every time, but when it did it really made a noise. Couldn't tell what was making the noise..... Thought I was hearing things!... Let me know if you figure it out. . please

 

[Blakers]

Mine did it too. I didn't know it even had an electric clutch on the fan - does it?

 

[David Muench]

There's nothing to figure out, it's working properly. The fan is big and noisy above idle, it moves a lot of air. When A/C is on and you're not moving fast enough to get good natural airflow through the condensor, the electric clutch locks up so the fan moves air. When you step on it and it's locked up, it takes a few seconds to decide to unlock, and during that time the fan gets noisy because it is moving a _lot_ of air. As soon as it unlocks, the fan slows down and quiets down.



As far as I understand it, it has a combination type setup. An electric clutch, but I also read it as having a thermal fluid clutch in there too. I am thinking that is to prevent the fan from over-revving when the electric clutch is locked up.

 

[Prairie Dog]

Originally posted by David Muench

I also read it as having a thermal fluid clutch in there too. I am thinking that is to prevent the fan from over-revving when the electric clutch is locked up.

I was thinking just the opposite, that the electric clutch engages because the thermal fluid connection slips too much and hence you get more air flow during the most critical times. Somewhat like the Horton fans operate on big rigs. Just a thought.



Scotty

 

[David Muench]

That could very well be, that makes sense.