slightly higher idle RPM with front defrost?

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salinity
Posts: 40
Joined: Tue Oct 17, 2017 11:28 am
Location: RI

slightly higher idle RPM with front defrost?

Post by salinity »

I noticed something over the past couple days - if I'm idling with the fan on in either front defrost or front defrost/floor selected I idle slightly higher (based on RPMs) than if I select vent or vent/floor. Does this make any sense to anyone? I assumed it was just a blend door that changes with the vent selection. I noticed this because I get an audible "chirp" at 800 RPM, but not 850-900 and the little uptick with the front defrost selected makes that difference.
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2007 Base
andrewclaus
Posts: 482
Joined: Tue Oct 03, 2017 6:38 pm
Location: Golden, CO

Re: slightly higher idle RPM with front defrost?

Post by andrewclaus »

Front defrost always turns on the A/C, which often requires a higher idle speed for the extra compressor load.
salinity
Posts: 40
Joined: Tue Oct 17, 2017 11:28 am
Location: RI

Re: slightly higher idle RPM with front defrost?

Post by salinity »

andrewclaus wrote:Front defrost always turns on the A/C, which often requires a higher idle speed for the extra compressor load.
Interesting - thanks for that info. My Cherokee doesn't have AC, so I've apparently been out of the loop for the last 12 years as far as the apparently common AC-assisted front defrost. I did notice the extra load (headlights dim slightly, etc) when turning the front defrost on last night.
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2007 Base
SeattleJeremy
Posts: 1170
Joined: Mon Jun 05, 2006 4:02 pm
Location: Tacoma, WA

Re: slightly higher idle RPM with front defrost?

Post by SeattleJeremy »

Yep, this is totally normal.
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