Another New Truck Question
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Senior User
Joined: Nov 2006
Posts: 137
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Another New Truck Question
I've noticed on my 06 Lariat that when I park it after driving it a while, and walk around the front I can hear a hissing noise coming from the radiator or A/C condenser. Sounds like an A/C type noise even though I'm not using A/C now because of the cold weather. I've assumed it's normal as my 06 Expedition does the same thing, but I thought I better ask. Thanks.............
Logistics Pro
Joined: Mar 2005
Posts: 2,536
Likes: 200
From: southeast PA
It's the pressure equalizing in the a/c system. It is 100% normal. A/c operates on the simple idea of a pressure differential, and when you turn off the compressor, the pressure wants to be equal on both sides of the system, so the high side pressure "bleeds down" to the low side until they equalize. You are hearing it because when you use the defrost (or I think any heat setting on this truck) it turns the a/c on automatically. Running the a/c with the defrost removes the moisture from the air before blowing it to the windshield for more effective results. You don't notice any cool air because the heater core temp overpowers the cold evaporator.
