A/C and fan motor

I have a 1998 Peterbild 379 with a cat. How much freon does the system hold when it is empty?

Next question. When I'm driving down the road the engine fan will not come on with the a/c on or off it doesn't matter. I replaced the high low pressure switch and the fan pressure switch. There was a fuse out by the fuse box. when I put it in the fan comes on but does not turn off. All the relays inside the dash are good. With the fuse out of the fuse box with the a/c on the fan comes on and off while idleing. I replaced the water temp sensor and the gage sensor and I replaced another sensor thats in front of the motor. I checked for broken wires. I could manually override it and it will come on at an idle or going down the road. By the relays there is a junktion box with 4 fuses that go in it. One was missing and I put a fuse in it, but not sure what it goes to. I didn't notice anything different when I put it in. Any help will be appreciated.

Thanks
Cindy

 

Thanks for the answer but that really wasn't my question. My question is how much freon does the system hold when it is comletely empty? The second question was about my engine fan, not the a/c fan. But thanks for answering I really appreciate it.