AC Compressor - Very Low Pressures - PeachParts Mercedes-Benz Forum

BayouFlyFisher · #1 12-05-2014, 10:03 AM

Well, my ac started getting warmer and warmer. Yesterday I checked the sightglass in the top of the dryer and it was, of course, full of bubbles. I got my R12 out and set to filling the system. When I first hooked up the gauges I was surprised to see the pressures were 0 (or even a little less than zero) and 90 at about 2000 rpm. I then slowly added freon until there were no bubbles. However, the pressures were still very low at about 5 psig and 100 psig. System is blowing ambient temperature air. The clutch kicks in fine when I throw the AC dash switch from off to on.

I'm thinking I've go a dead York compressor. However, I wanted to ask here if there is anything else that would cause these symptoms? My AC expertise starts and ends at "adding freon".

w123fanman · #2 12-05-2014, 10:17 AM

My guess is some sort of decent sized leak or the compressor. Check your sightglass again to see if there are bubbles.

leathermang · #3 12-05-2014, 10:26 AM

You need to see if you have a leak... and fix it before putting more refrigerant in....
what kind of refrigerant are you using .... I know you said Freon.... which technically means R12.... but some use it generically....
Great info in the archives already.... including my signature pointing to one....

I have the paper MB AC manual...and it specifically says NOT to use the sight glass for determining refrigerant level.... you may have already overfilled it using that... you should only use gauge pressures... but you need to set up the situation properly..... like having proper amount of air across the condensor..... and go slow..... overfilling the absolute worst thing you can do to an AC system.... it will work with several oz low....just fine...

eatont9999 · #4 12-05-2014, 10:29 AM

You either have a large leak in the system or the compressor is not functioning properly. What are the pressures if the system is not running? Any hissing or noticeable loss once the car is shut down?

BayouFlyFisher · #5 12-05-2014, 11:51 AM

Quote:

Originally Posted by w123fanman

My guess is some sort of decent sized leak or the compressor. Check your sightglass again to see if there are bubbles.

Thanks for the response.

No leaks that I know of, or if there are leaks they are small. The sightglass has no bubbles today after I added Freon R12 yesterday.

BayouFlyFisher · #6 12-05-2014, 11:54 AM

Quote:

Originally Posted by eatont9999

You either have a large leak in the system or the compressor is not functioning properly. What are the pressures if the system is not running? Any hissing or noticeable loss once the car is shut down?

Sightglass is not displaying any bubbles while running or while shutdown. I just went out and checked the pressure while the car was not running. It was 75# on both suction and discharge.

Sure is beginning to sound like compressor time.

leathermang · #7 12-05-2014, 12:23 PM

Did you read what I said about the siteglass ?

BayouFlyFisher · #8 12-05-2014, 12:38 PM

Quote:

Originally Posted by leathermang

Did you read what I said about the siteglass ?

Yes.

eatont9999 · #9 12-05-2014, 12:39 PM

Quote:

Originally Posted by BayouFlyFisher

Sightglass is not displaying any bubbles while running or while shutdown. I just went out and checked the pressure while the car was not running. It was 75# on both suction and discharge.

Sure is beginning to sound like compressor time.

Was that with the system off? That pressure is way too low unless it is very cold out. With the system on, there should be a large difference in low and high side pressures. With the system off, they are equal but usually higher than 75PSI.

BayouFlyFisher · #10 12-05-2014, 12:47 PM

Quote:

Originally Posted by eatont9999

Was that with the system off? That pressure is way too low unless it is very cold out. With the system on, there should be a large difference in low and high side pressures. With the system off, they are equal but usually higher than 75PSI.

System was off and ambient temp is in the low 70's.

eatont9999 · #11 12-05-2014, 01:00 PM

Quote:

Originally Posted by BayouFlyFisher

System was off and ambient temp is in the low 70's.

That's about right. Sorry, I was thinking of a different gas. If you run the system, what are the high and low pressures?

leathermang · #12 12-05-2014, 02:40 PM

He said 5 and 100 in the first post.....

eatont9999 · #13 12-05-2014, 03:43 PM

Yeah, today is not my day for reading comprehension.

Sounds like the compressor is not doing its job or there is no where near enough R12 in the system.

BillGrissom · #14 12-05-2014, 04:04 PM

No expert either, but I have fixed a few. 75 psi on both w/ engine off sounds about right for LA in winter. The 5 & 100 psi w/ compressor engages sounds strange. 100 psi I could believe, but 5 psi is way too low. Should be >20 psig. I would try adding more refrigerant. The sight glass doesn't mean much. If still way low, it sounds like a restriction on the suction side. You should feel a sudden cooling on the tubes right after the restriction.

BayouFlyFisher · #15 12-05-2014, 04:49 PM

Quote:

Originally Posted by eatont9999

Yeah, today is not my day for reading comprehension.

Sounds like the compressor is not doing its job or there is no where near enough R12 in the system.

When this problem started, there were quite a few bubbles showing in the sightglass. As I have done for the last 30-40 years, I added freon (R12) until the bubbles were either gone or mostly gone. In this case, I continued until no bubbles were showing. I am still getting almost zero pressure reading on the suction side and a little less than 100 on discharge.

When the system is off and the engine is running, I can see liquid move (as in jiggle) through the sightglass (not that is flowing, but jiggling around). So I'm pretty sure it's got quite a bit of freon in it, if not actually full. I guess since it looks like I am going to have to replace the compressor, I may try to put more freon in tomorrow as a last shot.

I know that earlier this year I added a small bit of freon and at that time the pressures were more like 20-30 suction and 180-200?? discharge. Those were the kinds of pressure I was expecting when I hooked up the gauges this time considering there were no more bubles showing now than there was when I got the almost normal pressures.

I think I am going to Punt! I will probably order a Sanden kit tomorrow. I will check around and find a shop that remove the R12 from the system. I will then install the new compressor, hoses, and dryer and pressurize the system with nitrogen to check for leaks. Although changing all that stuff will probably fix any leak I have right now.

I'm going to stick with R12 as I have quite a bit of it still (10-12 pounds). I'll vent the nitrogen, follow what ever oil instructions come with the kit, then hook the vacuum pump to the system to remove any O2 and moisture (it is humid down here!) and recharge the system.

Thanks for the feedback everyone. I just can't really think, based on the pressure gauge readings and the feedback I've gotten here and on other forums, that it's anything other than the compressor.