I’m guessing your FW is 50 amp service and you said you were tripping a 20 amp breaker. Sounds like you are using adapters to plug into a regular household outlet in your garage. This can be a problem depending what else is drawing current in the FW or possibly in your house on the same circuit. I used to have this same issue on my TT with 30 amp service plugged into a household outlet. Especially in July and August when it is the hottest. Try running your AC in the evening after the outside temperature has cooled down. See if it runs longer than 30 minutes. If that works, you might see if you can find someone with a 50 amp box or generator where you can get 30 to 50 amps of continuous power and see if that solves your problem.