Where do I start with A/C restoration?

I think all I need is for the system to be recharged (on an 84 300sd). All of my climate control buttons function and the heater works. Some times ther is a delayed reaction when changing the controls but that's about it. The A/C blows cool but not cold air.

My mechanic told me he can recharge it with R12 and that R12 is pretty expensive. He also informed me that the weak link with MB HVAC systems are leaky AC hoses which are also expensive.

My car sat for almost four years before I began her restoration. Before I pay to recharge my system, is there any sort of shade-tree diagnostic test I can do to check for leaks or other malfunctions?

[D.Blake]

hotskillet,
On my 83 SD, I had leaks on the manifold hoses and the thermo expansion valve (located next to the evaporator under the dash). Look for oily residue near connections and on the large hoses. Small ones carry liquid and are less likely to leak. The R-4 compressor can also be a source of leaks. If you have the system recharged, be sure to have the flourescent dye put in. Much easier to find the leaks. Hope this helps

[GregS]

The most important thing is to find the leaks (which are often obvious by a black oily residue at the location of the leak), and to ignore anyone who tells you he will convert it to r-134a for you. As you will hear many people say on this board, these cars just don't cool well with r-134a. And since the r-12 is the most inexpensive part of the a/c repair job (no matter how expensive it is in comparison to r-134a), stick with the r-12. You'll regret it if you convert.

GregS

Greg is right on the money here. The only thing I would add is that the MB is no more or no less prone to hose leaks than any other car. They're just hoses.

Find any leaks, repair them, thoroughly evacuate and charge with R12. R12 is coming down in price, don't pay over $25 or $30 per pound max.

Hope this helps,

[MT_Merc]

I haven't checked lately, but the cheapest I ever found R12 for when I was thinking about fixing my brother's AC and our van was something like $45 per lb.; some places wanted as much as $90. I hope LarryBible is right about it coming down because 75% of the cars out there that originally came with R12 simply do not have enough condensor to really work with 134. If you can find R12 for anywhere near that, then, as mentioned, don't even think about converting it. I converted our van because I knew there would be other leaks even with new seals and because it would have taken something like 4.5 lbs of R12; even though it has a relatively massive condensor the cooling is adequit at best. If you want good AC in an R12 system, you're stuck with two choices; either make sure the system is sealed up tight and stick with R12 or be prepared to replace at least the accumulator/drier and condenser (with a parallel flow--I've got one in my Fairlane and the cooling capacity for its size is an amazing difference from tube and fin). That's my thinking on it anyway.
I'm not sure what direction I'll take on our Mercedes. For one thing, I want to replace the old York compressor with a more efficient Sanden. If I did that, I'd do all new lines with o-ring fittings. The old condenser would probably also have to go. The one remaining issue, were I to decide to go with 134, would be the evaporator. I don't have any idea what the 123's have for evaporator capacity, but if it's as limited as the rest of the system then it's not going to cool that great no matter what goodies you add. Then again, it's not like that's going to be a big concern on this car for a while

[Eric Eliel]

The A/C system in my (new to me) 123 was just checked for leaks last night using a Snap-On sniffer.

Leaks: MAJOR leak at the pressure switch on the receiver dryer. Very small leak on the front shaft seal of the compressor. Minor leak at the expansion valve, discharge hose, suction hose next to the compressor and the hose between the discharge hose and the condensor.

These are the typical places for leaks on these cars. The leak at the pressure switch is so bad its no wonder the car wouldn't hold a charge.

Now if someone would post the part numbers for the hoses for me, I'd be......too cool.

My Tech told me to keep the r12 configuration. The bad news: he was quoting something like $75 oer pound of r12. Does anyone in the Bay Area know of a good shop for A/C issues or cheap r12?

[MT_Merc]

About ten years ago you could go to any parts store and buy 12oz cans of R-12 for less than $5. Now you need certification to buy it (thank you, all-wise EPA). There used to be a few sites that listed R-12, so you could check prices and shop around based on that, but I can't seem to find any of those sites now. Unfortunately, it's probably going to be hard to find reasonable prices on R-12. Even if the wholesale price is coming down, most mechanics aren't going to be in a big hurry to pass the savings on.

Go to one of the auto a/c sites and take the online open book test and get your 609 EPA certification for about $15. You then can buy R12 on ebay or anywhere else legally. On ebay it is as cheap as about $12 per pound right now.

A shop that is charging $75 per pound is soaking the daylights out of you.

The reason it is going down, I believe, is that the cars that use it are now at least 10 years old and more and more of them are hitting the wrecking yards every day.

Good luck,

Is there any specialized equipment you need to recharge the A/C?

Thanks for thinking outside the box!

There is indeed the need for special equipment, but there is also a need for special knowledge. If you decide to take it on, I strongly recommend getting a good book and do some studying. You can get a good book for about $15 at www.ackits.com.

The equipment you will need will be a gauge manifold set for your car. You will need one set for R12/22/502 and a different set for R134a. There are products available to let you convert one to the other, but you should not mix them.

You will also need a vacuum pump. You can get a commercial one or make one from an old refrigerator compressor. Don't try using a venturi unit.

You will also need some various other tools and items such as a vent thermometer.

I have been around auto a/c since my Dad went to a three day course and then started installing and servicing auto air conditioners in his independent auto repair shop in 1957. If you don't know what you're doing you can damage systems and even injure yourself.

It's a good skill to learn, but approach it dilligently and carefully. If you do, it can be rewarding.

Hope this helps,