We noticed today while driving around that our 1998 EX 4 cyl makes a very slight "grinding" noise when the fan is on and the A/C button is in. The noise is intermittent and from the driver's seat sounds like it is coming from the passenger side of the engine compartment. We don't hear that noise when the A/C is off and the cabin fan is going at the same speed, so probably nothing to do with the blower. After we got home I popped the hood and listened while my wife turned the A/C on and off. The compressor would make a single click when the button was pressed, presumably the clutch engaging, but I couldn't hear anything that sounded like that grinding noise in the engine bay. The engine bay did become noticeably louder though, even on the passenger's side, just not with a grinding sound. Maybe it is a little low on refrigerant? I have not looked at the records but it must be at least 5 years since any was added. Despite whatever this problem is the A/C cools very well.

The other thing is that I believe the IAC valve is not working properly since at idle the RPM falls (some) when the A/C kicks in, one of the things the IAC is supposed to prevent. Also the car will stall when in park or neutral if the motor is rev'd to 3000 RPM and then the accelerator quickly released - then the RPM falls past the idle point without slowing down and the car stalls. It never stalls in normal driving but probably would in a panic stop. It starts right back up again though. Can an IAC make grinding noises which are audible in the cabin? I'm wondering if the compressor might be working right but the IAC is being noisy trying to keep the RPM steady.

 

Had a shop evacuate and refill the refrigerant today. They said it was about half a pound (so let's call it 8 Oz.) low.
This page

https://www.4s.com/media/5421/four-s...city-guide.pdf

says that this car takes

02-98 All Eng. - 23.00 Oz. R-134a; 8.45 Oz. PAG-46 ..

So it was about 1/3 low. For 6 years that's 1.33 oz/year, which isn't horrible.

They couldn't hear the noise, which didn't surprise me, some days we hear it, some we don't.