I was reading the thread about 3 in 1 relays, and I thought I would post on how I handle it with fractional HP Tecumseh compressors.
A good friend at the local Tecumseh distributor sent me the following PDF that shows what relays and overloads are used on all small Tecumseh compressors. It only takes about 8 relays to cover all the pumps. I put them in a small box with a copy of the PDF, and it's great to be able to say, "your start relay is bad, but I have one in the truck".
When I did this quite a few years ago, I think it cost about $xxx (not much) for the initial stocking.