What causes the screaming of the belt when the defroster is turned on? When it is just the heat turned on, it is fine. Is this a tensioner gone bad, or belt needs replaced?
1997 Avalon Screaming belt when defroster turned on on 1997 Toyota Avalon
Defroster will always turn on the AC compressor. So, it would create additional drag on the belts normally...and if the compressor is wearing or has an issue, could be even worse. Could be a simple belt replacement, but make sure if you have the belt off that the pulleys turn freely with no issue.