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R12 to R134a Conversion Chart & Formula
Retrofitting a unit from R12 to R134a refrigerant requires you to adjust the charge accordingly. The volume of r134a refrigerant is lighter than the same amount r12 refrigerant. This not only is important to know for commercial refrigeration units, but it also is vital when making repairs on HVAC equipment and even cars. Fortunately, we have an R12 to R134a conversion chart and formula to retrofit appropriately.
R12 to R134a Charge Conversion Formula (pounds only)
A charge level between 75% and 85% is recommended when converting from R12 to R134a refrigerant. If no conversion information is provided, there is an easy formula to calculate the difference in charge level. This works when the R12 charge specification is listed in pounds. Take the R12 charge specification and multiply it by 0.9. Then, subtract that result by 0.25 pounds to get the proper amount of R134a charge.
Formula: (R12 Charge Specification x 0.9) – 0.25 lbs. = R134a Charge Level
As an example, let's say the R12 charge specification is listed at 2 lbs. You would do the following:
Example: (2 lbs. x 0.9) – 0.25 lbs. = 1.55 lbs.
This indicates that an R12 charge level of 2 lbs. converts to an R134a charge level of 1.55 lbs.
R12 to R134a Refrigerant Charge Conversion Charts
While the formula above is helpful, you might be strapped for time and need an answer quickly. Below is a PDF of tables that show R12 to R134a refrigerant charge conversions in pounds and ounces:
Additional Info from the Forum
In a discussion regarding R12 to R134a conversion, one of our members, Fixbear, provided some helpful tips. In addition to a full conversion chart (in ounces), he also provided the following consideration:
Equipment built for R-12 will be sized a bit too small compared to equipment built for R-134a. In order to do the same job, an R-134a system will need a larger compressor and larger heat exchangers. As a result, a system that is retrofitted from R-12 to R-134a will have lower capacity (run longer) and will probably develop higher head pressures (not enough condenser area).
Check out the entire discussion here.