No pressure reading on my AC system - Page 5 - PeachParts Mercedes-Benz Forum

cfh · #61 07-23-2015, 07:48 AM

"You just convinced me to take this job to my indie"

- Sorry, I didn't mean to discourage you! Using map-gas heat, combined with sharp, striking blows (not heavy bows, mind you, but use a big hammer) is not so difficult to do and can be useful in other areas too, to break loose stuck bolts (door strike hex bolts, motor mount lower hex bolts). Give it a go, it's not so bad once you try!

otto huber · #62 07-23-2015, 11:56 AM

Quote:

Originally Posted by cfh

"You just convinced me to take this job to my indie"

- Sorry, I didn't mean to discourage you! Using map-gas heat, combined with sharp, striking blows (not heavy bows, mind you, but use a big hammer) is not so difficult to do and can be useful in other areas too, to break loose stuck bolts (door strike hex bolts, motor mount lower hex bolts). Give it a go, it's not so bad once you try!

Removing the expansion valve only took about 20 minutes and required no excessive force. The tube fitting on the 17mm port required a lot of cleaning and was probably the source of the leak. Threading the bottom 22mm fitting back in has been one of the most frustrating jobs I've done on this car. Today I'm going to remove the grommet at the firewall and hope that that helps me get the angle I need to get that bolt started.

otto huber · #63 07-23-2015, 03:26 PM

I finally got that expansion valve installed. I'm now in the process of replacing every seal that I can get access to. In order to replace the seals on the two lines that feed into the back of the compressor, is it just a matter of removing that backing plate? Will removing those two lines adequately drain the compressor of it's oil, or is there a separate drain plug?

rrgrassi · #64 07-23-2015, 05:45 PM

It depends on the compressor used. The R4 does not have a sump or drain plug.

otto huber · #65 07-23-2015, 05:48 PM

It's an R4. If I have the car on ramps, maybe the oil will flow out when I remove those lines at the back.

rrgrassi · #66 07-23-2015, 05:58 PM

It depends on the oil level. Turning an R4 ports side down will remove some oil. there is also oil in the dryer, condenser, etc. When I rebuilt my A/C system, I flushed it with Methanol, and replaced the expansion valve, drier, pressure switches and the compressor. Also replaced all the O-rings and used the "Baby snot" o-ring lube, and BG Fridgi-quite oil. That was 10 years ago.

otto huber · #67 08-24-2015, 08:03 PM

It's been a while, but I finally completed the project, or so I thought. After replacing the expansion valve, dryer, aux fan switch, pressure switch, manifold hoses and getting the compressor resealed I charged the system with 3 cans of R12 and got enough cold air to know that the system is working at least adequately. I put in 42oz. of R12 which is 10 oz. below capacity because I only have 2 cans left and the season is almost over. The bad news is that 4 days after charging I can tell that I've already lost some freon

After all of the work I've put in, I'm so frustrated that the thought of selling the car or rolling it off of a cliff would probably feel better than having a fully functioning AC system. There is a hissing sound coming from the expansion valve that started just today and I think that that may be the source of the problem. I ran my finger along the valve and the lines and no trace of oil. Any ideas? Thanks

leathermang · #68 08-24-2015, 08:27 PM

How did you get the compressor 'resealed' ?

I am glad I was not back from a break when this thread was running...
there is a HUGE amount of bad / wrong information in it...
and an amazing number of things just left OUT...

I did not see any indication that you flushed the system ?
Did you take the post that said if the R12 had leaked out with the R12 to mean ALL the oil had leaked out ?

How many times do I have to say that the MB FSM FORBIDS the use of the sight glass for filling the refrigerant ? Do you people think I just made that up .. .for grins ?

Does no one read the AC thread in my signature ....which I think is the same one in VStech's signature ?

There is special oil for AC systems..... for R12 use NEW UNOPENED container of Castrol Refrigeration Oil - premium mineral lubricant for R12 AC systems packaged by TCC Cleburne Tx, Johnsen's cold flow 500 part number 6912

NYLOG ..which is used to coat the proper color o rings when putting the system together was FIRST MENTIONED IN 2001 - TWO THOUSAND ONE !!!!!!

Post number FOUR in this thread suggested reading Vstech's AC thread..
in THAT thread.. post number 24 I said this :

""I do not think the oil for the compressor is or should have to be counted on to seal the system.... as NYLOG of the proper color would be used on the o-rings and gaskets as the system is put together..
So the nitrogen would be used with the oil already in and spread out ..... do nothing except provide pressure and a SNIFFABLE refrigerant ( R22) to use as leak detection...
The compressor is not going to be used until the system is certified leak free...and the proper refrigerant is installed... so that can be used to carry the lube around and keep the compressor lubricated. ""

sleepstar · #69 08-24-2015, 09:13 PM

hissing from the expansion valve is somewhat normal. continuous hissing may indicate a system thats undercharged. if you were leaking enough freon there to hear a hiss your system would probably be discharged in a matter of hours

leathermang · #70 08-24-2015, 09:23 PM

Quote:

Originally Posted by sleepstar

hissing from the expansion valve is somewhat normal. .....

What kind of hissing are you people talking about ?
The TXvalve is designed to HISS.... it is spraying liquid refrigerant into the inside of the evaporator ... this is THE PHASE CHANGE which is HOW the AC works.....
Are any of you suggesting the hissing is releasing refrigerant into the Atmosphere ?
That is not supposed to happen...

otto huber · #71 08-24-2015, 09:43 PM

Quote:

Originally Posted by leathermang

What kind of hissing are you people talking about ?
The TXvalve is designed to HISS.... it is spraying liquid refrigerant into the inside of the evaporator ... this is THE PHASE CHANGE which is HOW the AC works.....
Are any of you suggesting the hissing is releasing refrigerant into the Atmosphere ?
That is not supposed to happen...

Last year when the AC was working well, I heard a short hiss when the AC went on and nothing more. Now it's hissing continuously and when I charged it up the other day and got cold air from the vents there was very little hissing.

To give a little more detail on what happened over the last 6 weeks; after changing my expansion valve and drier with switches, I had the system leak tested with gas at a local shop. The mechanic said that my manifold hoses were leaking and and that the leak on my R4 compressor was excessive. I had the front shaft seal replaced on the compressor. I put 7 ounces of PAO68 oil into the system and lubed all of my fittings and new seals with PAO68. I didn't have the system flushed, just had vacuum pulled on it for a couple of hours.The PAO68 has UV dye in it, so I can buy a black light and search for a leak. Like I said in my most recent post, the AC felt pretty good right after putting in 42oz. of R12.

eatont9999 · #72 08-24-2015, 09:46 PM

Quote:

Originally Posted by otto huber

It's been a while, but I finally completed the project, or so I thought. After replacing the expansion valve, dryer, aux fan switch, pressure switch, manifold hoses and getting the compressor resealed I charged the system with 3 cans of R12 and got enough cold air to know that the system is working at least adequately. I put in 42oz. of R12 which is 10 oz. below capacity because I only have 2 cans left and the season is almost over. The bad news is that 4 days after charging I can tell that I've already lost some freon

After all of the work I've put in, I'm so frustrated that the thought of selling the car or rolling it off of a cliff would probably feel better than having a fully functioning AC system. There is a hissing sound coming from the expansion valve that started just today and I think that that may be the source of the problem. I ran my finger along the valve and the lines and no trace of oil. Any ideas? Thanks

The TxV will hiss if you are low on refrigerant. You already mentioned it was low to start with. Charge the system until the sight glass runs clear on the hottest day possible. If it leaks after that, you need to find the leak. Ideally, you want to charge by weight but if you are adding a charge, go by the sight glass when using R12.

leathermang · #73 08-24-2015, 09:48 PM

If you did not have the system flushed.... how do you know how much oil is in the system ?

You did not think the system needed to be pressure tested to check for leaks ?.. like Vstech and I say ... which by the way is Industry Standard procedure... that is all we ever site... industry standard procedure.... Vstech is an HVAC professional ...

leathermang · #74 08-24-2015, 09:51 PM

Quote:

Originally Posted by eatont9999

The TxV will hiss if you are low on refrigerant. You already mentioned it was low to start with. Charge the system until the sight glass runs clear on the hottest day possible. If it leaks after that, you need to find the leak. Ideally, you want to charge by weight but if you are adding a charge, go by the sight glass when using R12.

THE FACTORY SHOP MANUAL FOR MB AIR CONDITIONING SPECIFICALLY FORBIDS USING THE SIGHT GLASS FOR ANY INDICATIONS DURING THE REFRIGERANT CHARGING PROCESS...
Using it to charge runs the serious chance of Overcharging your system... about the last thing you want to do.. since AC works on the differential between the high and low sides...

eatont9999 · #75 08-25-2015, 09:39 PM

Quote:

Originally Posted by leathermang

THE FACTORY SHOP MANUAL FOR MB AIR CONDITIONING SPECIFICALLY FORBIDS USING THE SIGHT GLASS FOR ANY INDICATIONS DURING THE REFRIGERANT CHARGING PROCESS...
Using it to charge runs the serious chance of Overcharging your system... about the last thing you want to do.. since AC works on the differential between the high and low sides...

I charge initially by weight. If you have a system that is under-performing or has leaked over the years, how do you charge it properly without knowing the exact charge weight?