98 XJ makes intermittent noise only when defrost is on
10-07-2018, 07:14 PM
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98 XJ makes intermittent noise only when defrost is on
I noticed if I turn on my defrost I hear a horrible noise coming from the engine bay. it's a loud grinding noise. Doesnt happen all the time. Anyone have any ideas?
10-07-2018, 08:14 PM
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10-08-2018, 10:51 AM
#7
Old fart with a wrench
Yes, the A/C runs in defrost. Auto designers decided to activate the A/C compressor when in defrost to keep the freon seals from drying out over the winter and having to recharge the system in the spring because the charge leaked out. GM has been doing this longer than most of you guys have been alive!
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10-08-2018, 12:17 PM
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Yes, the A/C runs in defrost. Auto designers decided to activate the A/C compressor when in defrost to keep the freon seals from drying out over the winter and having to recharge the system in the spring because the charge leaked out. GM has been doing this longer than most of you guys have been alive!
10-08-2018, 03:59 PM
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Engine: I6 4.0L
It's the compressor or the e-fan - As Dave mentioned "A/C" kicks on when the defrost is on and the O.P. indicated that the same sound occurs when the A/C is on.
There are no other moving parts and both the compressor and e-fan kick on when the A/C/defrost is on.
As previously suggested, unplug the compressor and re-try. When you start it up, leave the hood open and walk around to the engine bay and see if it's more clear where the sound is coming from.
You can also manually test the e-fan independently by jumping it directly to the battery and seeing how it runs.
There is a -small- off-chance that there is another engine mounted accessory (P/S pump, water pump, alternator, idler) that is bad and that's what's causing the issue (due to the extra resistance on the belt when the A/C clutch engages), but that's not likely.
Both the compressor and the e-fan are parts that are not uncommon to have a failure, so do some "noggin' pokin'" and let us know how it goes.
There are no other moving parts and both the compressor and e-fan kick on when the A/C/defrost is on.
As previously suggested, unplug the compressor and re-try. When you start it up, leave the hood open and walk around to the engine bay and see if it's more clear where the sound is coming from.
You can also manually test the e-fan independently by jumping it directly to the battery and seeing how it runs.
There is a -small- off-chance that there is another engine mounted accessory (P/S pump, water pump, alternator, idler) that is bad and that's what's causing the issue (due to the extra resistance on the belt when the A/C clutch engages), but that's not likely.
Both the compressor and the e-fan are parts that are not uncommon to have a failure, so do some "noggin' pokin'" and let us know how it goes.
Last edited by PatHenry; 10-08-2018 at 04:00 PM. Reason: grammar
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