how much R134a should go in?
 

I have an evacuated/converted to R134a 93 F150 with 5.0.

How much R134a should go into this system to properly charge it? Thanks.

Usually, anywhere from 70-80% of the weight of the original R12 charge is about right. Start with the 70% and check performance. Add an ounce at a time until you get ideal performance.

Steve

If you're doing it without gauges, then your doing it wrong.

Who said anything about "without gauges"?

The 93 parts (cond, evap core etc) are the same size as the 94 -95 models.
So use that charge weight. which is 33 oz

!!!!ABSOLUTELY WRONG!!! when converting to R134a.

If you do that, it will be so overcharged it will likely blow something out....

Steve

Who said anything about 'with gauges'?

Oh really.
91-93 models held 44 oz
94-95 models hold 33oz ,,,75% of what was used before in R12.
Same evap, condenser, comp volumes.

But hey I've only done thousands of retrofits in the past 19 years.
I was making the math simple for the question asked.

I interpreted "that charge weight" to be the R12 weight of 33 oz. Your post was not explicit in that the old R12 charge was 44 oz.

When placed in perspective with your additional information, your math is correct.

Sorry, but I took it the opposite way from what you meant and wanted to be certain that noobs didn't make a serious mistake.

Steve

I've done several R12 to R134A conversions and I always install a High Pressure Cut Out (HPCO) switch to prevent "blowouts" due to overpressure. Can't find them locally anymore so I bought the last two I needed from JC Whitney. With an HPCO I charge R134A to 85% of the R12 charge weight. OBTW, when you convert be sure you get a new accumulator that has desiccant compatible with R134A. Also, get an orifice tube (red/white) for R134A and adjust the compressor low side cycling switch for best performance. Check this link: http://www.forparts.com/techretrofit.htm