Hey guys when my ac compressor is on, the engine gets louder, and when i turn off the ac in the car, there is a whistling noise coming from the compressor, almost like a jet engine powering down, also the ac doesnt hit its coldest unless i am driving and the final symptom is that i checked my freon with a gauge and its in the warning area, 70-75psi i believe.

mine has a slight ticking/rattling noise.. the engine getting louder happens when you turn the A/C on in any car i believe, but if its a rattling or something, like mine, im not sure whats wrong

It might just be low on R134a. Mine made a lot of noise at lower temperatures (around 70 outside) when it was low on R134a. You may need to have it vacuumed and recharged with R134a and oil.

my ac shows its at 75psi, so it seems overcharged, are these symptoms of an overcharged system?

You can't tell from the low side pressures - you need to have the pressure from the high side with a large volume of air flowing through the condensor and the car rpms around 1500-2000.

my ac shows its at 75psi, so it seems overcharged, are these symptoms of an overcharged system?

Under what conditions did you measure the 75 psi? Was the AC switched on with the car running? Was the compressor engaged?

If the car was running AND the compressor was engaged, 75 psi could be a gross overcharge or a compressor that’s not doing its job. Since it does cool down when driving I’m thinking that the compressor isn’t “sucking” like it should. Don’t laugh, it actually works very much like an engine. The “low-side” connects to the intake of the compressor and the “high-side” connects to the output of the compressor. If the compressor has some broken reed-valves on the intake side – a common failure with this compressor – then it won’t pull the low side down to ~30 psi where it should be. I know this because I just went through this on my ’97 528i. The picture below is one I found on the net, but my compressor had the same problem. I’ve circled the broken reed-valve.

Another thing to think about – when you measured the 75 psi, was the needle in the gauge resting calmly on 75 psi, or was it shaking in the vicinity of 75 psi? If it was shaking, then that’s another indicator of a faulty compressor. If it was “calmly” resting on 75, then the system could be overcharged.

Another possibility is that your auxiliary fan is not running like it should be. You should check that also. If the aux fan is not running, the high-side pressure will be excessive and this can contribute to the excessive low-side pressure reading.

Keith

Can you damage your ac compressor with a non-functioning aux fan >? or its just not gonna cool at idle ?

Can you damage your ac compressor with a non-functioning aux fan >? or its just not gonna cool at idle ?

My gut tells me that excessive pressure is going to shorten the compressor life - how much, I don't know.

im pretty sure it was locked on 75, ill check again when i can, if it is overfilled, how do i evacuate it?

and yes, the aux fan is running fine

im pretty sure it was locked on 75, ill check again when i can, if it is overfilled, how do i evacuate it?

At this point I'd say you really need to figure out what the high-side (commonly called discharge) pressure is.

Before you go any further, take a look at:

http://www.instructables.com/id/How-to-Repair-Automotive-AC/

I just found it a few minutes ago but it may be very useful. According to his write-up, high suction pressure can be attributed to several things in addition to those I've mentioned. You may have an expansion valve stuck open.

If that's the problem, it's less expensive than a new compressor but it's still a pain. You'll need to get to the evaporator to replace the expansion valve. A shop is likely to tell you that the entire dash needs to come off. That's BS, at least on my '97 528. I had to remove the glove-box and a few plastic covers, but it should only take an experienced (and honest) tech about 15 minutes to get to that part.