AC compressor noise on shutdown

[1981_300sd]

I swear I have so many problems with the AC in this car.

It is finally working but now when I turn off the AC there is a strange loud noise that comes from the compressor area.

It is a new compressor (year old).

At the start of summer there was amost 0 pressure in the system (cap was broken and letting the pressure out of the low side). I just charged the system with 18 ounces r134 (the kind that has 2 ounces oil and 16 ounces r134). That was not enough so I added another about 6-8 ounces of just 134 (no oil). I have been told that a lot of the oil stays in the system when there is a leak so I added some that did not contain oil. Could a lack of oil be making that noise? I mean it at least has 2 ounces so even if low it shouldnt make that noise, or is there a flaw in my thinking?

In searching I see that could be a loose belt but would that only happen when the ac is turned off?

Thanks all.

[rrgrassi]

What kind of noise? I can hear the compressor clutch engage and disengage, each being a solid click.

[TylerH860]

Sounds likea bad clutch, or the beginnings of a locked up compressor.

I had the same symptoms a few months ago, and it slowly degenerated to a smoking belt on a locked up compressor. It was blowing cold all the way to the end.

[JCSC2]

I am interested in hearing what the noise sounds like too!
My 85 300SD is making a very loud piercing wine/hiss noise when the compressor is turned off. Like it's releasing a lot of pressure. Any thoughts of what that could be?
Also my A/C has been converted to R134 a long time ago. The A/C only works well(somewhat) if the car is steadly moving at a good rate of speed. But when you stop at a stoplight or in stop/go traffic it starts to blow out hot air? Any ideas would be greatly appreciated.
Didn't mean to highjack the thread!

[TylerH860]

Originally Posted by JCSC2

I am interested in hearing what the noise sounds like too!
My 85 300SD is making a very loud piercing wine/hiss noise when the compressor is turned off. Like it's releasing a lot of pressure. Any thoughts of what that could be?
Also my A/C has been converted to R134 a long time ago. The A/C only works well(somewhat) if the car is steadly moving at a good rate of speed. But when you stop at a stoplight or in stop/go traffic it starts to blow out hot air? Any ideas would be greatly appreciated.
Didn't mean to highjack the thread!

My '85 500SL is on R134 and I believe it makes the same noise. A loud tick and hiss that lasts less than one second. It hasn't gotten worse in the 5 years since the AC work was done, so I don't worry about it. The 300d only has the loud click, but its on R12.

[JCSC2]

Originally Posted by TylerH860

My '85 500SL is on R134 and I believe it makes the same noise. A loud tick and hiss that lasts less than one second. It hasn't gotten worse in the 5 years since the AC work was done, so I don't worry about it. The 300d only has the loud click, but its on R12.

Oh yeah, forgot to mention that it ticks BAD while it's on. You can hear while stopped at a light. But it either goes away when moving or the roar of the motor drowns it out.

[1981_300sd]

I dont believe it is the clutch, and if it is the clutch it does not sound right lol.

When I turn off the AC it makes a clunk, and just like the previous poster said, it sounds like pressure is being released - not like a clunk and pressure release that normally happens, but very loud.

Since the compressor is only a year old, I would hope that it is not on its way out - of course could be a defective compressor.

Do any of these options sound like they could be causing the problem?

1. Low oil

2. Too much freeon - overcharged (low side is showing 35 psi, dont have anything right now to measure high side).

3. Loose or streched belt

Thanks!

[TylerH860]

Originally Posted by JCSC2

Oh yeah, forgot to mention that it ticks BAD while it's on. You can hear while stopped at a light. But it either goes away when moving or the roar of the motor drowns it out.

I hope your compressor/clutch isn't starting its death moans. I'm kind of cynical because that's what happened to me.

[JCSC2]

Originally Posted by TylerH860

I hope your compressor/clutch isn't starting its death moans. I'm kind of cynical because that's what happened to me.

Hopefully not, but probably is. This a replacement compressor. It replaced a compressor that had been installed only a couple months. It seized while my Mom was driving throwing out lots of black smoke! Seems like she always had to have a pound or so of R134 added all the time.

[Matt L]

Originally Posted by 1981_300sd

I dont believe it is the clutch, and if it is the clutch it does not sound right lol.

When I turn off the AC it makes a clunk, and just like the previous poster said, it sounds like pressure is being released - not like a clunk and pressure release that normally happens, but very loud.

Since the compressor is only a year old, I would hope that it is not on its way out - of course could be a defective compressor.

Do any of these options sound like they could be causing the problem?

1. Low oil

2. Too much freeon - overcharged (low side is showing 35 psi, dont have anything right now to measure high side).

3. Loose or streched belt

Thanks!

Don't forget:

4. too much oil
5. wrong oil used after conversion to 134a.

If you added PAG oil and your system contains any rubber parts that were previously running R12, it is likely contaminated with chlorine.

But first check for too much refrigerant (Suva, not Freon). You will need a high-side gauge for this. And that new high-side gauge will also come with a much better low-side gauge than you have.

The low side pressure doesn't tell you much about the refrigerant quantity because you have a variable-displacement compressor.

[TylerH860]

Originally Posted by JCSC2

Hopefully not, but probably is. This a replacement compressor. It replaced a compressor that had been installed only a couple months. It seized while my Mom was driving throwing out lots of black smoke! Seems like she always had to have a pound or so of R134 added all the time.

I can't recall exactly, but there are other parts in the AC that need to be replaced when you get a new compressor to prevent damaging the new one. anybody?

My Indy seems to think that some compressors don't like R134. He told me about a 300td that went through 3 compressors in 6 months, the last was filled with R12 and had no problems after.

[Matt L]

When replacing a compressor due to failure, it is important to completely flush and purge the system. The TXV can be damaged by small debris and should be replaced; it has to come off to flush the evaporator anyway. The dryer should be replaced whenever the system is flushed for the obvious reason, and also because it will trap anything coming through the condenser. I don't know if you have a parallel-flow condenser, but these are extremely difficult to flush and purge. Old tube-and-fin condensers are no problem to flush and purge.

[rrgrassi]

The NEW. not remanned Hodyon (Hanckock Iind.) can handle the 134. Just use the thicker GM spec oil.

I used a reman, and it started to get noisy. I tightend the belt a bit, and it was good for a few months. Then after the waranty went out, the clutch started spilling, squealing and smoking (smelled like over heated brakes). Turned out the idler pully bearings went out. So I now have the new compressor. Next month will be a year again, but so far, no strange noises, no acting up, no leaks.

When you change out a compressor, change the drier as well. Also invest in a high/low switch, that disengaes the compressor in the event of too much or too low pressure events, since 134 does operate at higher pressure. The switch is about $20. Change the expansion valve also and flush the system well.

[1981_300sd]

I doubt that it is too much oil, because the problem only happened recently after adding the non oil refrigerant. Last season, no sounds at all.

So I am going to try the following after the suggestions given:

1. Add small amount of oil to see if that makes the noise go away, at least a little.

2. Check the high and low pressures.

Little help please - how much oil should I use? one of those small 2 ounce bottles? Or maybe half of one, so one ounce?

Also, what should my MAX high and low pressures be? I know ambient temps change what they should be but lets say for between 80-100 degrees - what kind of pressures are we looking at?

If both of these steps dont work, im going to just ride the compressor out to its death, then worry about a new one

[rrgrassi]

They system holds 6-8 oz of oil. 8oz is ideal. Since there is oil already in the system, you would need to totally flush the system and start from scratch so that you will know how much.

Also, when there isa refrigerant leak, oil is lost as well.