A/C recommendations for the MB vehicles - PeachParts Mercedes-Benz Forum

vstech · #1 04-15-2011, 10:08 AM

OK.
the A/C systems in our cars have plenty of obstacles to removing heat from our cabins.
Clean bend free fins and tubes should be the first thing any of us do to our car's a/c condenser, AND evaporator.
next it the fan clutch, and aux fan operation.

pressures in these charts are what we want to see with a proper operating system

This thread is going to be full of answers for our various automobile systems!

adding fans may help a little, but the problem with the older 123's lies in the huge series coil up front. it does not flow like 134 needs, thus lower volume of charge is required to keep the system operating... that low volume cannot handle the heat of the cabin without serious pressure spikes, and pressure is heat, it's a mad cycle.
IF you can find a condenser from an 85 123 it'll help a lot. but you'll still be pumping with an R4 compressor... are your windows tinted? light color paint on the car?

Quote:

Originally Posted by Manual Life

There are no leaks. The system held a vacuum for 4 months and has been good for a couple weeks. The recharge wasn't yesterday.

Oil added, none was in it. The vacuum could not reach 0 without the oil. I assumed I had a leak but that wasn't the issue. After adding the oil the vacuum reached 0. I don't know how or why. It was recommended by an old mechanic.

I can exchange the 134 but wasn't sure I could locate some 12. I assumed it was difficult to come by. I can unload the 134 at a friends shop at no cost, as is didn't cost me to charge it, but where would I locate some r-12?

a system with some pretty big holes can hold vacuum for months and leak out pressure in a few minutes.
to test a refrigeration system with an operating pressure of excess of 200 psi with less than 15 psi of atmospheric pressure is crazy and a really bad idea.
if it held, it proved nothing, if it leaked it destroyed the dryer and added moisture to the system... neither solution is helpful in testing a refrigeration system...

This thread is going to be strictly edited, and will include only approved A/C practices.
quality hints and tips as well as rules to follow!

Links to DIY and other Climate control articles

Quote:

84 300D

After a year and a half I finally got around to charging my A/C. It's so nice to have it and enjoy the quiet of windows up.

And, I assume if I doubled up on the fans for the condenser I would have cool air full time. As it is it warms up a little at idle and I am thinking this is the result of switching from R-12 to 134.

If that's not the problem let me know and what I can do. If it is the problem has anyone doubled up on fans? If so which fans?

Otherwise it works very well. I am happy to see how cold it is. I heard rumors that even a good a/c system didn't get very cold on these old cars.

leathermang · #2 04-15-2011, 12:06 PM

Quote:

Originally Posted by billhard

If you are sure your system isn't leaking why not go back to R12? After I rebuilt the system on my 85 I charged with R134 and ran it for about 2 weeks until I was sure it wasn't leaking. Then I took it to a local AC guy who evacuated the r134 (even gave me credit for it) then charged me with R12. This wasn't cheap but it works really well.

For the record ...
Do you want to describe what you did with regards to the oil in the system ?
In other words... did you have to plan ahead and make decisions about oil based on what you planned to do in the future ?

The more usual way to check for leaks is to pressurize with Nitrogen and four ounces of R22 ( which the EPA allows you to vent legally )..
This would negate any potential oil compatibility issues .
And would usually cost less than having the R134a evacuated by a pro with the proper equipment charging for their time...

vstech · #3 04-16-2011, 12:35 PM

Quote:

Originally Posted by Manual Life

This thread exploded. In the case that you already did not know, I know virtually nothing about a/c systems. And, I had a tech from Aamco do the work. We did it at his house because he had everything required.

He added 2 oz. of a/c oil after the system was evacuated. Following the oil he added the 134.

When I say "0" I mean on the evacuation. Without oil the there was not a full evacuation.

As is, I'll go ahead and test the system with dye and go from there. In the meantime search for R-12

OK.
let's start over.
the oil was added to a functional system, or was the system cleaned out first?
zero on a refrigeration manifold gauge is open to the atmosphere. or simply pressure removed.
a properly evacuated a/c system will read pegged to 29" on the lower scale of the compound gauge. not zero.
and that is NOT the limit of the scale, at 28.9 inches of mercury, vacuum there are microns of scale between it and 29.2" perfect vacuum. I like to shoot for stable 1000 microns in automotive evacuation that will hold.
it's REALLY hard to go lower than 1000 in a semiherm system. it's nearly impossible in a leaking system to get it below 2000 microns. and it will not stay there long. oil can slow the movement of atmosphere into the system through the pores in the lines, and the spaces between the seals. but just adding oil to the system will not move it around enough to do it. it's gotta be fed through an operating system to spread.

Unless you are discussing scientific gauges...
then: One Atmosphere = 14.7 PSIA = 0.0 PSIG

Perfect Vacuum = 0.0 PSIA = - 14.7 PSIG

sjh · #4 04-16-2011, 03:31 PM

The units and standards used for pressure measurements are very confusing.

Normally atmospheric pressure is called 1 atm. Now the fun begins:

1 atm ~ 1 bar (there's a 1% error)
1 atm = 14.7 PSI (pounds per square in)
1 atm = 760 mm Hg (millimeters of mercury)
1 atm = 29.9" Hg (inches of mercury)

and just for fun

1 atm = 101,300 Pa (Pascal) = 101.3 KPa [Metric]

One other common identity is -

1 mm Hg = 1 Torr
1 mm Hg = 1,000 microns

Another source of confusion is what does one choose to call zero pressure. Normal atmospheric pressure may be defined as zero or a perfect vacuum may be defined as zero. The difference protocols are designated either "gauge (G)" or "absolute (A)". So -

At norrmal atmospheric pressure: 14.7 PSIA = 0.0 PSIG

At a perfect vacuum: 0.0 PSIA = -14.7 PSIG

I believe there is one other potential source of confusion but those experienced with AC systems will have to verify this statement. Starting at atmosphere and then drawing a partial vacuum the system would start at 1.0 atm and then progress to 0.8 atm, then 0.6 atm, etc.

In AC systems it appears they use gauge (G) readings and inches of Hg. So starting at atmosphere and drawing a partial vacuum the system would start at a reading of 0.0" Hg and then proceed to -5.0" Hg, then -10.0" Hg etc.

So at a vacuum the pressure would read -29.9" Hg and while it is not normally written the - 29.9" Hg is understood to be a gauge (G) reading and not an absolute (A) reading. And, from what I see in the AC literature, the minus sign is normally dropped and they usually don't say mercury.

So, at the end of the day, a perfect vacuum maybe indicated by any of the three statements -

Perfect vacuum = 0.0" Hg (absolute scale)
Perfect vacuum = -29.9" Hg (gauge scale)
Perfect vacuum = 29.9" (gauge scale, no minus sign, no mercury)

mako224 · #5 05-30-2011, 08:39 AM

Quote:

Originally Posted by leathermang

For the record ...
Do you want to describe what you did with regards to the oil in the system ?
In other words... did you have to plan ahead and make decisions about oil based on what you planned to do in the future ?

The more usual way to check for leaks is to pressurize with Nitrogen and four ounces of R22 ( which the EPA allows you to vent legally )..
This would negate any potential oil compatibility issues .
And would usually cost less than having the R134a evacuated by a pro with the proper equipment charging for their time...

Use 420A oil is compatable and boiling point of refrigerant very close to R12. Our HVAC Service Dept researched and uses it extensively on older commercial R12 HVAC Compressors. I have had it in my 88 BMW and 91 SL for over two years without a glitch. 420A does not require any "O" ring changes and or modifications, just charge and go.

vstech · #6 05-30-2011, 10:32 PM

Quote:

Originally Posted by mako224

Use 420A oil is compatable and boiling point of refrigerant very close to R12. Our HVAC Service Dept researched and uses it extensively on older commercial R12 HVAC Compressors. I have had it in my 88 BMW and 91 SL for over two years without a glitch. 420A does not require any "O" ring changes and or modifications, just charge and go.

it's a blend of 134 and 142, similar to freeze 12, if I read the chart correctly...

Hit Man X · #7 06-07-2011, 07:33 AM

Quick question,

what RPM is recommended for checking pressures on the chart? 1500-1800rpm?

JHZR2 · #8 09-03-2018, 12:45 PM

Quote:

Originally Posted by leathermang

The more usual way to check for leaks is to pressurize with Nitrogen and four ounces of R22 ( which the EPA allows you to vent legally )..
This would negate any potential oil compatibility issues .
And would usually cost less than having the R134a evacuated by a pro with the proper equipment charging for their time...

Generally I spare no expense to do a job right, but just thinking out loud... I have a Co2 extinguisher, a regulator and a good deal of r134a.

Would the pressurized leak test be viable with co2 and r134?

My understanding is that this would be done statically without the system operating, so oil miscibility and flow would not be a concern.

Just saves buying stuff I’ll hopefully never use again, and buying r22 (for which I have a license so I can procure, just like r12) merely to vent.

Thanks!!

ROLLGUY · #9 09-03-2018, 05:49 PM

Quote:

Originally Posted by JHZR2

Generally I spare no expense to do a job right, but just thinking out loud... I have a Co2 extinguisher, a regulator and a good deal of r134a.

Would the pressurized leak test be viable with co2 and r134?

My understanding is that this would be done statically without the system operating, so oil miscibility and flow would not be a concern.

Just saves buying stuff I’ll hopefully never use again, and buying r22 (for which I have a license so I can procure, just like r12) merely to vent.

Thanks!!

It is against the law to vent r134a, so I would just use the cO2 at around 250 psi to test for leaks.

Concerning O rings (above post), there are #6, #8, #10, and #12 used in these systems. Cars with the Denso compressor have a special manifold seal. Other than that, standard size O rings are used everywhere else.

Diseasel300 · #10 09-03-2018, 08:11 PM

Quote:

Originally Posted by ROLLGUY

Cars with the Denso compressor have a special manifold seal. Other than that, standard size O rings are used everywhere else.

Possibly later models. My '86 SDL has the factory manifold on it and uses standard O-rings.

JHZR2 · #11 09-03-2018, 11:58 PM

Quote:

Originally Posted by ROLLGUY

It is against the law to vent r134a, so I would just use the cO2 at around 250 psi to test for leaks.

Concerning O rings (above post), there are #6, #8, #10, and #12 used in these systems. Cars with the Denso compressor have a special manifold seal. Other than that, standard size O rings are used everywhere else.

Thanks very much!

It seems to be very difficult to find any set that has #6 size o rings. Do you recall where this size is used?

Thanks again!!

ROLLGUY · #12 09-04-2018, 12:05 AM

Quote:

Originally Posted by JHZR2

Thanks very much!

It seems to be very difficult to find any set that has #6 size o rings. Do you recall where this size is used?

Thanks again!!

On a W123 the drier has #6, Condenser a #6 & #10, and #12's for the suction line. The short hose from the hard line mounted on the motor mount arm is either a #8 or #10. The TXV uses #6, #10 & #8 (I may be wrong on the TXV, someone correct if needed). Either way, a complete HBNR O ring assortment is available from Harbor Freight. It has all the sizes needed and more.

Zulfiqar · #13 09-04-2018, 11:36 AM

Quote:

Originally Posted by JHZR2

Thanks very much!

It seems to be very difficult to find any set that has #6 size o rings. Do you recall where this size is used?

Thanks again!!

you can buy a correct vehicle specific O ring set from autozone etc, they are branded as santech and come in little baggies for about 5 dollars. They have all the rings including any special manifold seals.

I use these seal sets now on every car I do, no more hunting for correct sizes and the rings I get have an expiry date so I always get fresh rings for a fresh job.

leathermang · #14 04-15-2011, 11:11 PM

Some oils are specified for R134a and some for R12 and I think some will do for both.. but I do not know how well they will do for both in our NON SUMP Delco R4 compressors.. thus I have not investigated it..

Many auto parts stores.. if you get the $20 over the internet EPA license based on an OPEN BOOK TEST... will sell you R-12... you have to ask them for it...and many of the idiots at the front counter see a request so seldom they do not even know the store has it... but often getting it off Ebay is cheaper..

vstech · #15 04-15-2011, 11:23 PM

I'll start the ball rolling.

to properly test a refrigeration (A/C) system for leaks you need PRESSURE! it must be in the form of a gas. NO liquid can be present or it invalidates the test.
Standard test gas is Dry nitrogen. CO2 can be used as can any gaseous refrigerant, but refrigerants are NOT legal to vent, so it's not a good idea to use them unless you have recycling equipment.

testing for leaks with vacuum is a ridiculous plan. I know MANY shops and individuals think it's a good way to test for leaks. It is NOT!
on a rigid piped system (home a/c or refrigerators etc) vacuum can and is used to test for leaks as well as moisture presence... but a DIGITAL micron gauge is required for the test.
mobile refrigeration with flex lines, and semi hermetic compressors with a shaft driven compressor simply cannot reliably be tested with vacuum. the rubber will mask a vacuum leak test, and the crank seals will vent moisture into the compressor, and the dryer in short order...