Heat Crash deals damage. Its power depends on the weight of both the user and the target; the greater the difference between the user's weight and the target's weight, the greater the power:
This also applies to Heavy Slam. Using either on a Dynamaxed target will fail, while using either on a Pokemon that's used Minimize will cause it to deal double damage.
Heat Crash (Bulbapedia)
Heavy Slam (Bulbapedia)
