Did they change the AC hoses when retrofiting to R-134? R-134 gas molecules are smaller than R-12 and can bleed through the hoses. It was first thought that barrier hoses were needed to prevent R-134 from bleeding through the R-12 hoses. It was found though that the R-134 oil would soak into the R-12 hose and establish a barrier to prevent R-134 from bleeding through the hose. However, the old R-12 hose has to be in good condition or the R-134 oil will not establish a barrier to prevent the R-134 from bleeding through the hose. On my '77 I had to replace both of my hoses about 5 years ago because they leaked along the entire length. You can have the hoses rebuilt by many AC supply houses with R-134 barrier hose and at a very reasonable cost (I'm talking about home and business AC supply houses and replacing the hose portion using your old metal ends).
I second euro 287's good advice to let the car sit overnight to let escaping R-134 collect enough to be detected. I'll add to not stir-up the atmosphere before testing to find the escaping gas (like opening large doors to let the breeze in, turning on fans, etc.). Also good advice about charging the system.
Not cooling well can also be caused by too much oil. R-134 does not work as well if the oil content is too high (too much oil can also kill your compressor). Mixing the two different kinds of R-134 oil (POE and PAG) can also cause cooling problems. Also, R-134 oils absorb moisture more readily than R-12 oil and moisture in the system can also cause cooling problems requiring a good deep vacuum (27+ inches of mercury) drawn on the sytem to remove it.
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1977 300D: 300,000+ miles
American Honda: Factory Trained Technician & Honor Grad.
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