Well, I have to drain the water heater pan to the outside of the house but, I live in a condo and space is very limited, I have the a/c furnace above th water heater, can I hook
The drain pan pipe to that of the a/c?

You can if you can connect a small pump to the water heater drain pan and pump it vertically to the condensate line of the AC unit.

Otherwise water does not run uphill.

Where does the a/c condensate line go? IF it comes down to the floor can you run next to it? I don't suggest tying into it. If the condensate line gets plugged(which is not uncommon)it would back up into the water heater pan, posing a potential problem for the heater. I have seen this happen a few times.

Is the water heater on a outside wal? Let me know, Tom