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Discussion Starter · #1 ·
2008 300c 5.7L, I have a screeching noise coming from the belt but only when I turn on the heat, haven't tried to see if it makes noise when a/c on because it's winter. Would it be the A/C compressor even though I'm not using a/c just the heat?
 

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If you load up the electrics i.e. Lights, rear window etc does that cause the problem too? I'm wondering whether it's the alternator being put under load and you need a new serpentine belt and/or tensioner
 

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Discussion Starter · #3 ·
If you load up the electrics i.e. Lights, rear window etc does that cause the problem too? I'm wondering whether it's the alternator being put under load and you need a new serpentine belt and/or tensioner
No it only does it with the heat on, and I was going to replace the belt and tensioner anyways just to be safe, I thought it was the alternator at first also.
 

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Your tensioner has a mark on it to show where it should be (within limits). But if you look at it, it is easy to see whether it is at the "new" end (tensioner has long way to stop) or "belt stretched" (tensioner towards/at end of travel).

Sometimes, belts (when old) just get "hard and shiny" and can slip, even if tensioned; although that is more with vee belts; not the groove belts these have - but it IS possible. If you can get it to do the screech while you are watching; and spray water on the belt with a spray bottle and the screech changes pitch = that's it.

Probably easiest to just replace the snake belt if any doubt. Check tensioner/any idler bearings as well while there.
 

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If you're heater is on defrost mode (with the heating coming out at the base of the windshield, your a/c compressor is running...so it could indeed be your compressor.
Good point. Also comes on if in climate control (auto); if car senses humidity...... it then switches to "demist" and switches on A/C compressor to dehumidify.
 
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