slicky rick

we have variable displacement compressors in our cars. recently i had a leak on the discharge side of the compressor leading to the discharge line... this is the discharge port on the compressor itself. initially i thought it was a suction line connection which also had a leak. i had this repaired and the tech added 30ml of denso nd oil8.. however upon further inspection the main culprit was the discarge port of the compressor... i then proceeded to replace the errant o-ring which needed me to remove the compressor to access the port.upon removal of the compressor there was puddle of oil under the compressor, so i guessed the 30ml of oil added by the ac tech should just be right.. after replacing the single errant o-ring everything was good to go.. i also replaced the receiver drier and put additional 20 ml of oil in the drier... now the car is blowing ice cold! however, i am now hearing a sound in the engine bay that sounds like a pressure valve that is opening and closing.. the sound seems to disappear when the ac compressor is turned off.
when i removed the compressor i had to remove the plenum to access the compressor bolts... the car runs well which i suppose tells me that i returned everything properly... idle is smooth so leaks can be discounted... what could this be? i inspected the AOS lines and eveything seems connected properly... besides this "new sound" everything is working properly.... smooth idle, cold ac!! any ideas??

TheBruce

is it fully charged with refrigerant?? when I first got my car I had some weird intermittent noises at idle, particularly when I was coasting into a stop sign. sometimes sounded like elves chopping wood, other times it was a very pronounced sound coming from the expansion valve behind the dash. searched for it for months. thought it was maybe a bad ac compressor clutch so I replaced that, which was a pain in the ***. nobody had posted anything like it in the 997 forum but found one thread in the 996 forum talking about similar noises due to low refrigerant levels. I tested mine and it was in fact low. I topped it off and solved it immediately. zero noises ever since. what I suspect is with low refrigerant the ac lines resonate more (which was the chopping wood sound) and the expansion valve is louder.

weberlukas74

Check the condition of the AC compressor pulley and the belt that drives it. Make sure the belt tension is correct.

Also, check the AC clutch. A worn-out clutch or faulty bearings could cause the sound you're hearing.

Verify that the refrigerant charge is at the correct level.

slicky rick

thank you for the advices, AC compressor oulley is ok.. new compressor with only about 20k kms on it. Belt is also new, with less than a year when installed.. Belt tension i think is automatically done by the tensioner. i am not sure if we have a clutch for our ac compressors since we have variable capacity compressors... i put in more or less 850g of r134a into the system... i hope that amount is right...

irontmp

The new sound you're hearing is likely caused by one of the following issues:

1. Refrigerant Level: Check that the refrigerant level is correct. Too much or too little refrigerant can cause the compressor to make noise.
2. AC System Pressure: Ensure there are no blockages and that the pressure readings are within the manufacturer's specifications.
3. Oil Quantity: Verify that the total amount of oil added is correct. Incorrect oil levels can cause noise.
4. Compressor Clutch/Bearings: Inspect the compressor clutch and bearings for wear or damage.
5. Air in the System: Make sure the system is properly evacuated and free of air pockets.
6. Reinstalled Components: Check all components and lines moved during the repair to ensure they are secure and not causing vibrations.

Addressing these points should help you identify and resolve the source of the noise.

slicky rick

Again I make a big boo boo... I thought the sound was coming from the compressor, it wasn't!!! The sound was coming from the throttle body!! The compressor is positioned right under the throttle body... and I noticed that when I hear the noise the idle seems to falter a bit!! I am now trying to do a search on throttle body noises to diagnose the problem... thanks all for giving advice on the possible issues!! Truly appreciate!!