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Discussion Starter · #1 · (Edited)
When the car is idling with the trans in neutral and i am running the defroster, once and awhile I will hear the a/c clutch engade and at that same moment. My idle will jump from about 800 to 1200 rpms and then settle down to a smooth 800. That doesn't seem normal to me, or is it? Do I need a new a/c switch? Or is it the IAC starting to go out? When running striaght a/c it does not seem to surge or when running on just the heater vents. The car runs and idles perfect besides the ocasonal surgering during defrost mode.

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do you have the a/c on when running the heater? If so, i wonder if the a/c kicks on every now and then just to dry the heat out. Ive always heard people run the a/c with the heat just to take the moisture out of the heat. :dunno

Id say it seems close to normal to me.
 

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Mach1 FTW
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do you have the a/c on when running the heater? If so, i wonder if the a/c kicks on every now and then just to dry the heat out. Ive always heard people run the a/c with the heat just to take the moisture out of the heat. :dunno

Id say it seems close to normal to me.
+1 on that
 

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I <3 Boost
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do you have the a/c on when running the heater? If so, i wonder if the a/c kicks on every now and then just to dry the heat out. Ive always heard people run the a/c with the heat just to take the moisture out of the heat. :dunno

Id say it seems close to normal to me.
the heater doesnt use the ac pump but the defroster does

my car does the same thing but doesnt jump that high.... my car idles a little lower though. might just be normal, ive never really worried about it with my car.
 

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You can turn the a/c on when you turn the heat on even when not using the defroster..^People do this to keep the moisture out of it.
 

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I <3 Boost
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i see what your sayin now baker... for some reason i didnt understand what you were sayin. but yeah he said he has his defrost on so the pump is engaging every once and a while. sounds pretty normal.
 

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yes its normal. when the a/c comes on, it puts a load on the motor, so the iac raises the rpms to keep the motor from dieing. but it shouldnt go that high, only a few hundred rpms higher.
 

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It's funny...all this idle talk (and mine is a pain in the arse w/ idiling and the cams...) and the funny part is, I remember the old 5.0's having the same querky idling. I remember putting an E303 cam and converting to MAF on my 87' (only way it would even consider idling). Then switch the A/C on...poof, would stall at a light. My father works on city crown vic's (police cars) and sez they often having idling problems and "shut-offs" after a hard run then stopping. weird

But, the reason I actually posted :) On the Ford trucks...even if A/C is NOT selected on heat mode...the only position on the knob that will NOT use the compressor is the Lower/Foot heat option. Even if u put the selector on basic upper vent, it will use the compressor...use to drive me nutz listening to that thing cycling in the cold on my old powerstroke superduty...wondering if the stangs are similar, my AC is gone so...i wouldn't know.
 
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