: 1971 Fleetwood 75 A/C conversion

05-25-09, 10:39 AM
Hi, a friend of mine just converted his 1971 Fleetwood 75's A/C system from the "old" R12 system to the new R134A. The shop manual lists the weight of the R12 needed to fill the system. After the conversion the mechanics say he should need a different amount of R134a in the system. Is that true? More or less is required? Is there a percentage that he can use as a rule after a conversion is done?
He sais that the front A/C is cold, but the rear is not cold enough, he assumes it is because of the incorrect amount....

Highway Star
05-25-09, 01:17 PM
It takes less R134 due to the higher pressures used with that type of freon. I think it's something around 20-25% less than R-12. Was the rear A/C cooling good before the conversion?

05-25-09, 02:30 PM
It was good a year ago, and then the A/C died, and additionally he installed a new heater valve for the rear A/C. Now he sais, that the A/C in front is cool but not cold. So I think he has a charging problem for sure and maybe the valve is not OK.

Highway Star
05-25-09, 04:26 PM
He might need to get it re-checked with gauges to determine if it has the correct amount of R134 in the system. It's important not to have too much, as well as too little. The condenser (in front of radiator) must also be clean of debris (bugs, leaves, etc). The aluminum lines at the evaporator (at firewall) should be cold to the touch (with a/c running).

05-25-09, 08:01 PM
The mechanic is correct, typically most R-12 converted systems require less R-134a since R-134a has a latent heat of vaporization (the amount of energy required to change state from vapor to a liquid) of 47.19 (Kcal/Kg @ 0o C) versus 36.43 (Kcal/Kg @ 0o C) for R-12, and which translates into the 20-25% figure mentioned here.

Some converted systems, however, do need more, and typically you need more condenser as well as fan enhancements. The POA valve should also be adjusted for the different pressure/temperature relationship between R-12 and R-134a.

All this because a bunch of progress hating hippies in their drug induced daze decided R-12 was destroying the ozone layer. And it's only gonna get worse with king Hussein in office. Maybe you shouldn't even bother converting because R-134a is scheduled to be banned (contributes to "global warming").

They won't be happy until we have no air conditioning at all and ride around on bicycles.


05-27-09, 12:30 AM
If you fill with R-134, replace with 75% of the recommended amount for R-12.