I have a 2008 hhr ss, automatic with 36K miles. I just noticed today while i was waiting at a light, that when I turned on the air fan the boost pressure on the meter went from -20 to -10 and then went from -10 to -20 when i turned the air off. Is this normal? Has anyone noticed this before? As far as I can tell I havnt noticed any performance issues

 

Nothing to worry about I think, depending on the ambient temperature, the A/C compressor sucks up about 5-8 horsepower when its running. The ECM automatically compensates so you don't feel the idle speed drop, but the extra load causes fluctuations in manifold vacuum.

 

Oh I'm thanks the info but I don't have the ac on. It's just the fan that's on. That's what worries me.

 

Now that's something different, maybe the boost gauge is registering a voltage drop when the fan is on, weird.

Sorry I misunderstood, just assumed you had the A/C on.

 

Oh no worries man I appriciate the input. Idk I guess I'll see how things go. Maybe I'll have my mechanic check it oh if I notice it getting worse

 

Does the needle go up when the foot goes down ?

 

Yes of cource. It just seemed odd that the needle would move when I turn the air fan on. I never noticed it before until now. I wasn't sure if this was a common occurrence

 

I have never looked, I'll check it out next time.

 

Ok thanks for the help.

 

At the simulated stop light, (my driveway), mine doesn't move when the fan switch is activated or deactivated. AC, or just air didn't chance it. I can feel the drain on the system, electrical I suspect, and the Christine brain compensating for it, but I get no more than a flutter of a pound or so, hard to see with trifocals. Defiantly not 10 lbs.