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Rpms up and down

bearrug

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i have a 98 f150 with a 5.4 in it and When It Is Idling In Park Or In Drive ,when I Have The Defroster On The Ac Kicks On And Off Making My Rpms Go Up And Then When The Ac Clicks Off It Goes Back Down,i Know That It Is Normal For The Ac To Come On And Off But Not The Rpms To Go Up And Down, I Replaced Iac ,but Still Does It,and It Didnt Do It When I Bought It 5 Months Ago Thanks
 
blacksnapon

blacksnapon

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Staff member
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waynesville,mo.
The iac is designed to raise the idle whenever the a/c kicks on to compensate for the added drag the compressor puts on the engine. So, your iac is operating correctly. What is probably wrong is your a/c charge is low or too high (probably low), and the switches are intermittently shutting off your a/c. Get your a/c repaired, and it will settle down.
 
blacksnapon

blacksnapon

Moderator
Staff member
9,461
301
waynesville,mo.
F150 said:
Why is the AC compressor kicking on with the defroster?
Click to expand...
All vehicles are designed to do that. It keeps the freon oil circulating through the system, even in winter, so after a long period of inactivity, the compressor doesn't start up dry.
 
03 Big Red

03 Big Red

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NC
bearrug said:
i have a 98 f150 with a 5.4 in it and When It Is Idling In Park Or In Drive ,when I Have The Defroster On The Ac Kicks On And Off Making My Rpms Go Up And Then When The Ac Clicks Off It Goes Back Down,i Know That It Is Normal For The Ac To Come On And Off But Not The Rpms To Go Up And Down, I Replaced Iac ,but Still Does It,and It Didnt Do It When I Bought It 5 Months Ago Thanks
Click to expand...

I'm having exactly the same issue with my 03 SD 5.4. Is it possible that the collision shop that did my repairs over charged my AC?
 

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