Originally Posted by rclarke
If you hook them both together for extra air capacity set the pressure switches so that the second compressor comes on 5-10psi lower than the first. Most of the time only one compressor will come on and the second compressor will only come on when you are using a lot of air.
Thats what I'd do. When starting from zero pressure the little one will help build it up. Most of the time the "good" compressor will do all the work. The old one will be a backup and much better than nothing if the "good" one quits. Just pipe the tanks together.