Hi folks. This is going on a 76 450sl (107) that has already been converted over to R134a some 15 years ago. I just took possession of the car last year and this is the first summer I've had it...trying to to get the AC going. Currently blowing hot air, so figured I would try to charge the refrigerant. Purchased a recharge kit from Advanced with the gauge built into the hose. Followed the directions:
1. Engine idling, AC on max
2. Verified that the clutch on the compressor had engaged and was spinning
3. Connect quick connect on low side
4. Gauge reads "0"
5. Squeezed trigger for a couple of seconds
6. Gauge now reads "WARNING" but slowly drops down over the course of a minute back to "0".

I'm going to check the schrader valve tonight..totally slipped my mind to check that out. Any other suggestions of what it might be. I am assuming that if the compressor is spinning...then it is sucking correct?

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Birmingham, AL
2006 Audi A4 "Audrey"-daily driver
1976 MB 450SL "Marlene"
2000 Jetta VR6 "Julia"-traded at 220k miles
1997 Jetta 2.0Trek "Blanche"-traded at 450k miles YES 450,000 miles
1986 Prelude "Gladys"-died at 120K miles

You need to evacuate the system by putting it on a vacuum pump. Draw a vacuum of 30" and let it sit to see if it holds the vacuum. If not, give it a partial charge of refrigerant with a dye tracer. Use a black light to check for leaks, fix them and repeat the vacuum test until it is tight. It is a waste of time and refrigerant to charge a system without first making sure it is able to hold the charge.

230/8

I agree with the above. You need to visually inspect the system and see if you can find the source of the leak. It could be a hole in the hose, it could be a fitting broke off the condenser. If the system reads "0" now then the system is open. Putting more R-134 in will only let it leak back out.

Since the system is open the receiver/drier needs to be replaced. These cost about $20.

The system needs to have a vacuum pulled on it to remove moisture. This also helps to verify the absence of leaks. Skipping this step is a recipe for failure as the moisture in the system will combine with the refrigerant oil and create acid.

Once these steps have been done you can refill the R-134. You need a proper manifold gauge set as refilling R-134 is dependant on the high side pressure.

Look on the brightside - at least the car is already converted!

I appreciate your responses....since I don't have the vacuum pump or the gauges..i guess i'll take it to the mechanic...

Thanks!

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Birmingham, AL
2006 Audi A4 "Audrey"-daily driver
1976 MB 450SL "Marlene"
2000 Jetta VR6 "Julia"-traded at 220k miles
1997 Jetta 2.0Trek "Blanche"-traded at 450k miles YES 450,000 miles
1986 Prelude "Gladys"-died at 120K miles

HIJACK: I'm looking to recharge my already converted r134a system. I've read that you need to be certified to handle it, true? Can I buy it in stores like online? I had it recharged last year and it didn't hold, but I want it for an 8 hour trip I'm taking

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1983 240D 3.0T 4-speed manual, now sold

1989 Subaru GL Wagon 5-speed Touring Edition

You should be certified to safely handle any refrigerant product and work of automotive AC systems, and if you offer your services for sale to the public as an installer you must be certified. That said, you can still buy R134a and the related service products over the counter in most auto parts stores without presenting a certification number.