How much R-134 ?

Using a GOOD digital thermometer, have it installed at the pass side dash AC duct. Run the RV at 1200 to 1500 RPM's and on MAX cool(recirc). Have someone WATCH the thermometer. Then slowly add the 134a. The output temp will then slowly drop. Once the temp gets to a low temp and stops going lower and then starts to RISE, stop the fill. You have reached the saturation point. Just blindly adding 134a is not a good idea. Also, do NOT add any oil to the system. NOT NEEDED. Doug

If it's working your just going to add some aka top off

The total system amount doesn't matter, unless you evacuate it and refill using guages

Thanks all. 2.7 seems to be the number. We'll see.

If you add too much, even if it was partly cold before, it will then blow hot. Too much refrigerant in the AC system is as bad as too little. Then you have to take it to a shop that has the AC evacuation system and have the system evacuated and refilled.

Even using a gauge, it is easy to add too much. Don't ask me how I know.

Autozone or Walmart recharge kit. Attach it to the low pressure side of the system, add freon until the gauge is in the green. I've done this for years of three or four vehicles now. No problem. It doesn't fix leaks but then if the leak is real slow it may save you some $.

I would look for a leak first before adding R-134. Leaks will show up as an oily substance. Look especially close at your switch that turns your system on. Auto parts stores sell R-134 with a die and ultraviolet light to help identify small leaks. Does your system blow any cold air?

Auto-Zone, and some other large auto parts stores will LEND you a set of gauges, along with an instruction manual, if you want to go that way.

The Evans-Tempcon total R-134a refrigerant charge capacities for various vehicle/chassis can be found here:

RV Applications Refrigerant Charge Guide

You can also use your hand by feeling the low pressure line (larger of the two) coming off the compressor. That line will be cold to touch. It should also sweat when it's humid out. Do not over fill your system as that will cause it to ice up. As stated above the best way is with a good set of gauges.

If you don't have gauges, use a thermometer in the AC outlet duct and stop adding Freon when the temperature has reached it's lowest point.