Tensioner "knocks" very loudly when AC is on. Stops immediately when I turn it off. PLEASE HELP! - watch video

[BKennedy]

It could be something not the AC compressor, but the noise only happens when the AC is on. The AC compressor puts more strain on the belt, which in turn puts more strain on all the components run by that belt. If you remove the belt you should be able to check by wiggling the individual components. It there is anymore than a tiny amount of play, they need to be replaced.

You can also get a piece of tubing, put one end to your ear, and carefully touch the other end to the body of the alternator, AC compressor, power steering pump, to see if one of them is making the noise. Do not touch it to pulleys while they are moving, obviously. You can get close to the pulleys to listen this way too. It's a old school mechanic trick. I have an old stethoscope from my EMT days I use for this with the bell removed.

 

[Momma Dulce]

Is there an automotive shop in the area that deals/specializes in vehicle HVAC issues?

Peter

I'm not sure! I'll check!

 

[JohnelP]

Hope it is already known there is an electromagnet (acting like a clutch) between the ac compressor pulley and the ac compressor itself. when ac is off, the electromagnet is powered off and there is no coupling between the ac pulley and the ac compressor itself. once you turn on AC, the electromagnet is activated, and the ac compressor starts spinning. i would check the commands to the electromagnet. the "vibration" of the belt tensioner is because there is uneven load (or strain). Block the elmagnet to on and see what it happens. i would trust the mechanics to change the AC compressor, belt and tensioner. but if the command to the AC compressor clutch is messed up, part itself may behave weird

like this:

 

[Motorhogman]

I'm not sure! I'll check!

Most radiator shops do a lot of AC work.

 

[Momma Dulce]

Hope it is already known there is an electromagnet (acting like a clutch) between the ac compressor pulley and the ac compressor itself. when ac is off, the electromagnet is powered off and there is no coupling between the ac pulley and the ac compressor itself. once you turn on AC, the electromagnet is activated, and the ac compressor starts spinning. i would check the commands to the electromagnet. the "vibration" of the belt tensioner is because there is uneven load (or strain). Block the elmagnet to on and see what it happens. i would trust the mechanics to change the AC compressor, belt and tensioner. but if the command to the AC compressor clutch is messed up, part itself may behave weird

like this:

Thank you for your very detailed note and video!

 

[MAS Tequila]

I had this start a while back.

About a month ago the engine went south when the water pump dumped into the engine.

$5200 later, the same ac compressor and no noise.

 

[Metalface]

I had this start a while back.

About a month ago the engine went south when the water pump dumped into the engine.

$5200 later, the same ac compressor and no noise.

My AC clutch is iffy, while the water pump is inspected and fine. I recently had replaced my belt before I had the "knocking tensioner" problem, and indeed, I got a belt that is "too long." Haven't replaced it yet but the only variable that changed when the knocking tensioner begun was the belt being changed.

 

[Momma Dulce]

I had this start a while back.

About a month ago the engine went south when the water pump dumped into the engine.

$5200 later, the same ac compressor and no noise.

Is the water pump something that can be diagnosed or does it have to fail to know it's bad?

 

[peterk9]

Is the water pump something that can be diagnosed or does it have to fail to know it's bad?

Since the pump is inside the engine, I believe the only way to tell that it is leaking is to check the weep hole or the oil on the engine dipstick for signs of coolant. Once it has mixed with the oil, it should appear as a 'milky' colour on the dipstick.

Peter