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Engine RPM drops and almost stalls when using defroster or air condition

Tiny
SCOTTIETISSUE
  • MEMBER
  • 2004 FORD F-150
  • 4WD
  • AUTOMATIC
When I use the air conditioning or defrosters the motors rpm drop and stalls only when I use them if I don't its fine what could be the problem?
Friday, September 5th, 2014 AT 12:55 PM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,758 POSTS
If this only happens when you are at an idle, most likely, the idle air control solenoid is bad. It is responsible for maintaining engine idle speed. When you engage the AC compressor, there is a load put on the engine. At that point, the PCM should signal to the IAC to slightly increase idle speed to accomedate the added load. If the IAC doesn't respond, the engine may stall.

NOTE: The AC compressor engages both when you turn the AC on and when the defroster is used. In the defrost setting, the AC is used to dehumidify the air coming into the vehicle to help clear the windshield.
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Friday, September 5th, 2014 AT 8:33 PM
Tiny
SCOTTIETISSUE
  • MEMBER
  • 2 POSTS
I could be driving down the road at 55 with air conditioning on it will be fine except when I slow down to like 5 or 10 mph is when it dogs out and stalls. Same thing you think?
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Saturday, September 6th, 2014 AT 12:32 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,758 POSTS
Yes, I feel confident that either the IAC is bad or there is a vacuum leak. Since it idles smooth without the AC, that makes me lean toward the IAC.
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Sunday, September 7th, 2014 AT 8:27 PM

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