Heil furnace no ac the transformer has been replaced twice keeps burning out

You have a low voltage short somewhere. It would be helpful to know if the transformer burns out right away, or last awhile...
In any case, the next transformer needs to have a circuit breaker on it, so you can RESET it instead of having to replace it! You DO NOT have to use an OEM transformer from Heil. Get one with a circuit breaker.
Then, take note of when the breaker trips. Does it happen as soon as the outdoor unit comes on? Probably a short in the contactor. Does it happen when the blower comes on? Could be a short in the blower control board.
If none of this helps, you could check here: My A/C Is Broken - Help Me Fix My Central Air Conditioner
There is live troubleshooting help there.