In "Charizard Chills", an Ice Beam from Poliwrath instantly freezes Charizard into a big block of ice. However, in "The Symbol Life", when May worries about Charizard being directly hit with an Ice Beam from Articuno, Max says "It's ok. Against a Fire-type, that attack should have no effect."
So why did it take effect in the previous series then?
The weakness types have changed slightly over time.
This image of the Pokemon Red and Blue weaknesses show that a Fire defender is neutral (i.e. 1x) versus an Ice attack.
While this more modern version of the chart for the current generation shows Ice attacks as less effective (.5x) against a fire creature.
This page shows the old versions together and you can see there's a change between gen1 and gen2 to reduce the effectiveness of Ice vs Fire creatures.
Gen2 matches the Gold and Silver which comes out around the same time or slightly after the episode you've been watching.
So the answer appears to be that between the two episodes the weakness chart changed to make Ice attacks less effective on fire creatures. Which is why originally Charizard was encased in Ice, but later (Symbol life is 6 seasons or around 340 episodes later) he can shrug off such attacks.
The frozen status condition can be inflicted on any Pokémon who isn't an Ice-type themselves, whether or not they are resistant to Ice-type attacks While Fire-types in general take less damage from Ice-type attacks, and it doesn't really make sense that a creature with an ever-burning fire on its tail can freeze, Charizard can be frozen as readily as any other Pokémon.
Such eccentricities with typing are abundant in the anime, particularly in the early seasons. In the Kanto-era episodes, Pikachu defeats no less than four Ground-type Pokémon with electric attacks, which shouldn't have any effect on them whatsoever.
Things happen in the anime for the purposes of narrative and dramatic importance. Levels are unimportant, Pokémon have moves they shouldn't know, and, yes, typing mechanics are occasionally ignored or minimized. When an ice-type move needed to be effective against Charizard, it was, and when it was more important to obey the fire v. ice dichotomy, it did.
Charizard is a fire type, but he's also a flying type.
Ice type moves are not very effective against fire types, but they are super effective against flying types. As such, an ice type move used against Charizard will have normal effectiveness, as shown in the earlier episode.
In addition, being a fire type does not prevent a Pokémon from getting frozen. So even though fire type gained a resistance to ice in later generations, as Jontia noted in his answer, the most likely explanation is that Max is simply wrong on this account and Charizard will not like getting hit by an icebeam.
Being frozen is different from being dealt damage.
A pokemon can be frozen from a hit that deals 1 damage, which will render them unable to attack until they thaw out.
Well the answer is pretty obvious
Imagine this in your mind
A dedenne pokemon a stunfisk and a pikachu are all standing out in a field of grass but are not aloud to move for the sake of this test
They all are electric type pokemon with the ability to absorb electricity
But heres the important and differing strengths/weaknesses of each
Pikachu is a Steel/Electric type
Stunfisk is a ground/Electric type
Dedenne is a fairy/Electric type
They all are Electric types but they also all have different type moves therefore increasing or decreasing thier resistance to type moves of opponents in which are either super effective against or not very effective
Also theres weight difference and the fact that some pokemon train more then others and evolution, z moves, mega evolution and other factors in play in the Pokemon universe.
Its Confusing but basically its many factors that have to be taken into account in a pokemon battle all at once
