I have Rudd Ultra Series Central Air and I'm wondering where reset button is on the unit

Hi, as far as this unit having a reset button on it, it would not. If this unit is a gas fired heater, it will have reset buttons on a couple of its safe controls such as the high limit switch, or roll out switch that sometimes will trip and will have to be reset. If the unit is not on in the cooling, you need to check to make sure the thermostat is calling and that there is voltage to both the indoor and outdoor units. Check the circuit breakers to see if maybe one has tripped. On the outdoor unit you will have a disconnect box mounted near the unit. It also will have 2 fuses inside of it. They may be hidden from view behind a panel cover, but you may have blown one. Your unit is a 3 1/2 ton system according to your model number in case you ever need to know. But yes, this is what you need to do if the unit stopped cooling, is to locate the breakers for both the indoor unit and outdoor unit to find if a breaker has tripped for some reason, such as it overloaded. If you do find one tripped, it will be in the midway position. Shut it off hard, and again back on hard to reset. Please keep me updated on what you have or have not found, so that I can walk you through getting it back on line.
Sincerely,
Shastalaker7
PS On the indoor unit, this model should have a 3 to 5 amp fuse on the main control board just behind one of its panels. It may have a inspection view hole you can see through to see if the led red light is on. If so, this will tell you if the indoor unit has power to it if the light is on.

Turn your power off first before you take your cover off one of the resets are on the bottom rail where the bottom of the units top fits in its a red rubber button