My car's a/c is converted to r134a. Went to use the air in June and didn't blow cold. Tested the pressure, it was very low. Three weeks ago, I added some refrigerant with sealant and it worked fine. Today, it doesn't work again.

So, I suspect I have a refrigerant leak in something other than a hose (which the sealant should have taken care of). What's the most likely culprit?

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1982 240D automatic
Odometer quit at 307K...about 325K now

compressor, condensor, expansion valve, evaporator
o-rings


I just bit the bullet and took it to an AC shop and had them diagnose mine for $40

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Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

Tested with gagues, added freon with sealant? How about dye? If you did add dye, buy/borrow a UV lamp. They are available at NAPA, penlite style AA battery or handheld flashlight 12V style. First look at the water drain tube for the evaporator. Is there any dye present? If so, the evaporator is leaking.
Now check your hoses and joints. Pull the passenger knee panel and check the expansion valve. Check the condensor, compressor and drier. If you can use the light in a dark garage, so much the better.

The chemical structure of 134A will allow it to leak through old hoses. Any old hoses should be replaced.

Even though it's sold as a "cure all of your a/c woes", I would never use sealant, EVER. It clogs everything up and creates problems. A/C shops hate the stuff, their equipment is equipped with filters and detectors to stop it from turning a three thousand dollar machine into a boat anchor. Some of the better a/c shops will not repair or warranty a vehicle with sealant.

If there was no dye present, has the car/engine/undercarriage been washed? If so, there is a chance any tracer dye was washed away.

Alan

__________________
DO IT RIGHT THE FIRST TIME, DON'T BE A HACK
Political Correctness is NOT part of my vocabulary
and finally FIGHT CRIME...SHOOT BACK

'82 240D Stick
'85 300D Auto
Drove my first MB at age 16 1960 300SL W190

An a/c system is a "CLOSED" system. It doesn't use freon, it circulates it. If you are low on freon, you've got a leak somewhere. Find and fix the leak first.

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'83 240D (for sale)
'84 Harley FXRT
'85 300CD Turbo (Sold)
'85 500SEC (for sale)
'04 Dodge Dakota Quad
'06 Harley FLHTCI
'97 SL320

The R-4 compressors are known to leak at the front seal.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Adding refrigerant with sealant has fixed my a/c woes every time I've used it (on other cars). Of course, I've never had a car this old before.

I did call a local a/c place and they were not pleased to hear I'd added sealant, although he seemed to relent a little when I explained that the refrigerant came with sealant in it--he admitted that a lot of what you buy at Pep Boys and the like does nowadays. They are supposed to call me back this afternoon, though it's getting close to 5.

The stuff did have a neon yellow color to it, so there is some dye, I assume it's a UV dye as well. I can get a UV light of some sort and poke around. Thanks for your help, everyone.

__________________
1982 240D automatic
Odometer quit at 307K...about 325K now

Correct.

If the front seal is leaking, and the compressor is original to the car, it's not a big job to replace with the correct clutch remover.

If you end up replacing the compressor with a new unit, it probably will have updated seals for the manifold hose. Old style R4's used "O" rings, new style use a colored metal and rubber seal. The compressors usually come with red, green, silver and yellow seals. I think the suction side was red and the return was yellow. I could go into it in depth, do a search for "stepped ports".

The reason for the different seals is this. The R4 was used by other auto makers, and different manifold hose block designs required different seals.
For example the thickness of the red seal is .15, green seal is .22 and the yellow seal is .12

I made the mistake once of using the wrong combination of seals. The block appeared to be parallel to the compressor, but is was off just enough that it would not hold a vacuum. I had made the mistake of using the red and green seals. I did not have to use the inserts that came with the seals.

NAPA can order the correct seals from their TEMP catalog. They are listed by color. Red 407277 Green 407278 Yellow 407279

Alan

__________________
DO IT RIGHT THE FIRST TIME, DON'T BE A HACK
Political Correctness is NOT part of my vocabulary
and finally FIGHT CRIME...SHOOT BACK

'82 240D Stick
'85 300D Auto
Drove my first MB at age 16 1960 300SL W190

The suction side is the return side.

Here is what worked on my '82 300D:

NAPA Part # TEM 407278 (Discharge) & TEM 407279 (Suction.)

Or Four Seasons (Temperature Control Division) part #24357 & 24358

Two things:
1. There are two types of "sealant". One is just a fluid that causes rubber (o-rings and hoses) to swell a bit. The other is a fluid that turns solid on exposure to moisture in the air. It's this second one that you don't want to ever use, except when your alternative is to just give up on the a/c system permanently.
2. Took it to an a/c shop, they looked at it with a UV light. Fortunately, just 2 leaky o-rings on hoses. The guy mentioned that the material used for o-rings on R12 systems is different than for R134a and mine were likely never changed when the system was converted. So, looks like I got off easy this time.

__________________
1982 240D automatic
Odometer quit at 307K...about 325K now

I would also hesitate to use o-ring conditioners in a system. They can swell the o-rings to the point where they start leaking, where you had no leak before.

I bought several cans of the stuff with o-ring conditioners a few years ago, and it's not going into any car that I own. I haven't figured out what to do with the stuff. I'm thinking of giving it to charity, so they can sell it to someone who would have just gone to the Zone for the same stuff.