Frigidaire Model RBG3 94U presume it is at least 25 years old. Dimensions of oven inside are 17" x 18-1/2"

When it is on bake cycle, do both upper and lower elements engage, or just the lower.

In some ovens the lower one is on. In a convection mode, both may be on. In Broil, only the top one is on. Are you having trouble with temp control or baking? I'd set it to broil to see if the top element is working.

If both come on you probably have a bad switch. Only the bottom element comes on when turned to bake. DrTom4444