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'72 Cutlass Supreme R-134a

Old May 19th, 2014, 03:01 PM
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'72 Cutlass Supreme R-134a

I bought a restored ,72 Cutlass Supreme which has the A/C changed to R-134a. I've had it about three years and the A/C needs a shot of R-134a.

On the sticker that is on the evaporator, it says that it has been changed to R-134a, but then it has 8.5 lbs. listed as well.

Does anyone know if that the correct spec as it seems low to me. If it's incorrect, how many pounds should I bring it up to for a refill?
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Old June 7th, 2014, 07:22 PM
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You need to use gauges to measure the pressure on the high and low sides. The weight of refrigerant matters only when charging a completely empty system as there is no way to determine how much is still in a charged system, but the high and low side pressures can show when the proper amount of refrigerant is reached.

By the way, that 8.5 pounds sounds very odd. Most systems use around 3 pounds.
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Old June 10th, 2014, 06:20 PM
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There are a couple of rules of thumb when changing to R134A.
One is that you will only use about 75% of the charge capacity that R12 required. Just look up the R12 specs and do the math.
The second is that you are not supposed to top off 134A, but I do it all the time in .2 lb increments. Your car should have a sight glass. Just top up until the bubbles disappear.
Using a set of gauges will help tremendously. The high side should be approximately 2.5 times ambient temperature. The low side someplace in the 30-35 range.

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Old June 10th, 2014, 07:23 PM
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Vintage Air say's ignore the sight glass when charging their 134a systems, go by the temp/pressure only. Temp/pressure charts are easy to find on Google.....
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