How cold should A/C be in 116 300SD - PeachParts Mercedes-Benz Forum

WANT '71 280SEL · #1 08-08-2003, 08:47 PM

Just got a '79 300SD. It is still R-12 and has never been touched, even has the original r/d. Should this be as cold as my dad's recently converted 300E? It was converted to r-134a. My A/C in the SD is horrible. Their aren't any leaks. Should a car like that have very cold A/C?
Thanks
David

#2 08-08-2003, 11:49 PM

I'm guessing here, but I think if everything is working
correctly the a/c should work as good as any car.
The fact that it is a 79' does not make it inferior
as far as its capability to cool.
I had my 82' diagnosed with a bad compressor
and the shop only put enough freon in it to try
to get the compressor to work. (3/4 lb) I was
on my way after a $45 dianostic charge and another
$40 for freon thinking I need a new compressor.
The A/C did work after that, not super cold but
noticable. They said they put a dye in the system
to detect where it was leaking, since freon will
work forever unless it leaks out (their words).
They said that the compressor may have started
working since the added charge of freon, and
that I never noticed the dye because an ultra-
violet light is necessary to see it. So although
I may have a leak, a full charge of freon may
have taken care of everything, though it may
have not lasted if I had a leak. So what I would
do is a search about how to be liscensed to buy
freon and try to charge it yourself. From what
I've read it costs about $20 to get liscensed
and then you can buy freon cheap enough to
make up for the $20.
I hope you got a deal on the 79', my 82' just
sold for $1,000 and the buyer was extremely
pleased. You inquired about it in July but never
responded to my email. I thought mabee you
were too flooded out in fort wayne to get to Mi.

leathermang · #3 08-09-2003, 08:45 AM

Yes, the age should make no difference... the condition is all that matters...
An Auto air conditioner will leak over the years due to the design.. at the very least the compressor main shaft which has the clutch on it is designed to get oil to the front shaft seal by pushing it out of the system.. a tiny bit at a time....
If yours IS working... but just not cooling ENOUGH... that is a really good sign... and you will probably have great success doing a simple refresh of your R12/receiver/dryer....
But since you will have to open it up to do that... I really would suggest you read up on what it would take to flush your system before putting those things on it... which would include putting NEW OIL into the system.... and a really good vacuum job on it....

WANT '71 280SEL · #4 08-12-2003, 03:24 PM

so you think that with just replacing the r/d it would make it colder? I have a relative with all the r-12 tools like guages, vac pumps, etc.
Thanks
David

Kestas · #5 08-13-2003, 05:01 PM

Yes, your a/c should be cold. Considering the age, you are probably just low on refrigerant. Freon is a "slippery" molecule and hard to contain forever.

I disagree with leathermang that a "refresh" of the refrigerant or dryer is needed, unless he meant topping off the freon. But don't just nilly-willy change the dryer. It's unnecessary work and not a part that usually goes bad. You don't want to unnecessarily open up the system unless you have to. There are no maintenance parts on the a/c sytem. The parts either work or they need to be replaced.

Since you're getting SOME cooling, the first step is to visit your relative, hook up the gauges, and get the pressure readings. You'll probably find the high side to be under 100 psi. It should be way up there over 200 psi. Post back with your results.

#6 08-14-2003, 08:31 AM

Start by running it on max at about 1,500 RPM for five minutes then check the sight glass. If it is showing bubbles then it is low on freon.

Good luck,

leathermang · #7 08-14-2003, 10:31 AM

Kestas,
He has said he has the original Receiver Dryer.... you think that replacing a 24 year old Receiver dryer , which would probably cost about $35 dollars is " willy Nilly " ..... ?

And concerning the " a part that normally does not go bad " NOT TRUE... when they get OLD the bag which holds the silica jell just ROTS off or vibrates to death... and contaminates the rest of the system...

I would carefully get this Receiver out and replaced and not take the chance that while adding refrigerant it decides to let go....

Kestas · #8 08-14-2003, 11:50 AM

Yes, I had that scenario in mind when I posted. If David is getting SOME cooling, I doubt that the drier has disintegrated. To replace the drier as a maintenence procedure opens up other issues, such as maintaining proper lubricant levels, new gaskets, evacuating, and recharging, all of which involve a lot of work and grief.

I'm not an expert on silica bags, but yours was the first time I saw concern about silica bags getting brittle and needing replacement as a matter of preventive maintenance. Perhaps I should change the drier on my 32-year-old Cutlass, even though the a/c works fine.

WANT '71 280SEL · #9 08-14-2003, 03:32 PM

I have a little bit of a problem when looking for bubbles like Larry said. I can't even see through the hole! It is so old that it is faded! The whole r/d looks cracked maybe? The paint is chipping off. No doubt it is the original.
Thanks
David

leathermang · #10 08-14-2003, 03:42 PM

This is from a wonderful site.... aircondition.com

http://www.familycar.com/Classroom/ac1.htm#EVAPORATOR

The receiver-drier is used on the high side of systems that use a thermal expansion valve. This type of metering valve requires liquid refrigerant. To ensure that the valve gets liquid refrigerant, a receiver is used. The primary function of the receiver-drier is to separate gas and liquid. The secondary purpose is to remove moisture and filter out dirt. The receiver-drier usually has a sight glass in the top. This sight glass is often used to charge the system. Under normal operating conditions, vapor bubbles should not be visible in the sight glass. The use of the sight glass to charge the system is not recommended in R-134a systems as cloudiness and oil that has separated from the refrigerant can be mistaken for bubbles. This type of mistake can lead to a dangerous overcharged condition. There are variations of receiver-driers and several different desiccant materials are in use. Some of the moisture removing desiccants found within are not compatible with R-134a. The desiccant type is usually identified on a sticker that is affixed to the receiver-drier. Newer receiver-driers use desiccant type XH-7 and are compatible with both R-12 and R-134a refrigerants.

---------------------------------------------
If you like site glasses you might consider installing one of the see through models which allow you to put a flashlight below so you can see what is happening ( limited to the natural limitations of any sight glass in the first place ).