98 villager a/c

Hi,

I'm workingon my folks' 98 villager a/c system. It's got the dual a/c set up. My dad says it's cooling OK up fornt, bu the compressor is kicking onanad off continuously. "Like the run signal is on constant.

Sounds low on refrigetant to me.

How much R134 does this system hold?

Thanks
Bill