ADC and Support have near the same level of tankiness. Would Ashe work as a good support considering she would have a utility slow which can be buffed by her q,frozen mallet and rylais crystal scepter as well as her ult stun?
My opinion on this is that Ashe would make a bad support. By support I talk about one going full support, i.e. relying on passive gold, masteries, GP/10 items as a way to grab gold, and a champion that is here for the sole purpose of enabling an ADC to grow in power.
Why is this? Because her kit is made to deal damage over utility. Of course, she has a nice slow, but she lacks a real crowd control ability to mitigate the other ADC damage. If you take other supports, Lulu Thresh and Janna have a shield, Sona has the Z (W, on US keyboards) power chord that decreases the target's damage, Soraka Sona Taric and Nami have heals, Taric Lulu Thresh and Leona have stuns that stop the ADC from attacking.
In what way can Ashe compete in this area? Ok, her ult can stun, I'll grant you this. But this comes with a huge cooldown. Basically, if the other team attacks, you can only not lose by doing more damage and killing them.
Second point, the squishiness of supports are usually well addressed by their kit in late game. Shields, heals or armour boost grow with the champion level. Ashe doesn't have any of this. So, unless you buy armour and health, you will still be squishy.
Third, all support champions have some small way to boost their ADC on other characteristics like: attack speed, movement speed, AD, AP. Ashe has none of these.
However, this does not mean that Ashe would be a bad pick for the second bot-laner. But then you can't really say you are playing her as a support. If your objective is to completely overwhelm the other team and force them to hug their tower, this may be a good pick.
Edit: On the slow component I did not talk about
First of all, we need to read this on wikia and Ashe's page as well.
Ashe's Frost Shot slow cannot be buffed by either Frozen Mallet nor Rylai's Scepter as her Frost Shot does not proc on hit effects. Only her AoE slow can be stacked with Rylai's (as Frozen Mallet is for AA only).
So it is really not a good idea to build Frozen Mallet on Ashe in any cases. Rylai's Crystal Scepter... hum 2900 gold for 80AP and 500 health? What will Ashe do with 80 AP anyway? A Randuin's Omen would be far more interesting for her.
And final thought: does Ashe really need a boost to her slow? Really?
The answer "no" has already been nicely explained in response to you, as Ashe doesn't have many of the characteristics of a support. But if you really want to try her bottom lane to complement your ADC, for fun I recommend CDR Ashe.
The idea is to maximize your utility slow and poke trading potential by capping your cooldown reduction at 40% as soon as possible. This lets you spam Volley every 2.4 seconds, Enchanted Crystal Arrow every 48 seconds, and Hawkshot every 24 seconds at max level. It also adds debuffs to your Volley that scale well throughout the game and enhance the damage of your teammates.
Who it works against
This works best against teams who you can disengage from and kite, or simply outpoke. For example, this pick could work against a Nasus, Renekton, Udyr, Pantheon, Shen, Ryze, Elise, and a variety of mid/short range casters and bruisers. If they have to walk up to you to kill you, you can probably kite them. This would most likely fall flat against heavy poke like Caitlyn and Nidalee, or bruisers/assassins with reliable and persistent engage like Vi, Ahri, Kassadin, and Zed.
The playstyle is simple, learn your Volley range and abuse it to hell. Most champions without long-range engage and hard CC will not be able to punish you for volleying into them. Make a habit of moving after you volley so you don't commit too hard to your poke. Use it to poke champions while you siege towers, just beware of tower aggro when you get in range as Elder Lizard true damage ticks over a long duration. Also use Volley to peel for your team when you are being chased. The slow is extremely effective against a grouped team and they will have a hard time catching you and your team. Even if they catch you, they will have a hard time continuing to your team while the slow from your Volley is still burning them. Save your ultimate for protecting your ADC or for a long-range gank across the map when you can coordinate it. Avoid auto-attacking unless you aren't being focused; you attack very slow with this build and your damage output will be minimal, even with your Focus passive.
The core is Spirit of the Elder Lizard, Ionian Boots of Lucidity, and Chalice of Harmony. This nets you:
Your core costs a total of 3880 gold, which is pretty pricey but achievable mid game for a support who is doing well. There is no hope for achieving this during laning phase unless you manage to extend that phase, so expect to play a very passive early game without your core.
The final item to cap your CDR is Black Cleaver, with the Brutalizer component giving CDR. The armor shred on your Volley is very effective, but Black Cleaver is quite a costly item for a support. You want to build it only after you get your three core items. Chalice is necessary for mana sustain only; you aren't intended to finish Athene's Unholy Grail, nor will you ever make enough gold to finish it after you've purchased your other items. Tear of the Goddess -> Manamune is an option for mana sustain, but it doesn't provide as much mana regen as Chalice. Also, the likelihood of you finishing Manamune is extremely low. The other items I mentioned are far more crucial to finish.
In the case you do happen to get a lot of extra gold income, build as much AD as you can after your core to scale your Volley. I recommend Last Whisper so your base physical damage and AD scales, then Infinity Edge. After those, purchase red potions before finishing Athene's Unholy Grail - Athene's doesn't give many more stats over the base Chalice compared to the stats you get from red potions.
Never build Rylai's Crystal Scepter or Liandry's Torment. Although they have natural synergy with Volley's slow from Frost Shot, you have no means of scaling the magical damage. By the time you can afford those two items they will be completely useless purchases. You're much better off scaling more AD or tanky items to help survive longer engagements.
To clarify the preferred build path:
Typical support pots + ward + gold income start -> Spirit Stone -> Spirit of the Elder Lizard -> Ionian Boots of Lucidity -> Chalice of Harmony -> Brutalizer -> Black Cleaver -> Last Whisper -> Infinity Edge -> Red potions -> Athene's Unholy Grail
If you do finish Athene's you can sell your boots since you no longer need the 15% CDR. Purchase boots of your choice.
For gold income I recommend Spelltheif's Edge. It may give little in terms of stats, but Ashe is extremely good at expending Tribute stacks with her Volley and can easily make it the most gold efficient start. Ancient Coin is good when you don't expect to be able to poke. I don't recommend Relic Shield - the gold sharing is nice but without the execute it's hard to coordinate with your ADC. CDR Ashe also builds almost no HP, so the fully upgraded Face of the Mountain's active ends up doing very little.
As for masteries, I always recommend taking the 4 point investment for Sorcery. It's 5% CDR accessible to any choice of mastery build. The rest is up to you, I prefer tanky masteries so that I'm always a presence in teamfights.
Her kit would make sense, the passive on Hawkshot would be the only thing wasted.
Apart from the slow and stun, she doesn't have much to offer the ADC (or herself) in the way of saving, but can harass and stun to setup kills I suppose, so an agressive kill lane might work. She would also benefit from building things like Zeke's Herald herself, as well as supporting the team.
Still would make more sense to play her as the ADC IMO. I think I'd personally be looking for a support with more traditional "supporting" abilities when you get into the later team fights.
Ashe is difficult support to play. Actually she lacks the burst and utility for support.Her ability are not very strong in early game.And if her passive charged faster,she could somewhat become viable player for support.
Anything is viable in the right situation. If the enemy team has only melee champs with no gap closers at all, then a support ashe would rock. She could just kite them all the way and let the adc get the final hit. It all depends on the situation. If you are up against Caitlyn, or any ranged champs actually, your Ashe with an inventory full of wards and a bit of hp will get hit pretty hard without the entire team protecting her.
Short answer: No, this will generally not be viable, but that doesn't mean you can not win a lane with it.
2 days ago I started to play ashe support. It's a viable picks, but can be counter quite easily. Here is my build : yellow support item, sightsone (of course), blade of the ruther king randouin, cdr boots, and last whisper. I pick up ad/as/armor pen/armor runes and supports masteries.
With this build, ashe support works extremely well with caitlyn adc. You have a really strong poke, thanks to cait"s aa and ashe z(or w) and aa. If you and the cait're playing well. You can poke them until near their death even before they hit level 2. But this build doesn't work too well late game, because your damage output is still low even if you get fed, and you can't do a shit against some champions (like akali). But her ults bring a lot to every lane if you manage to pull off some good ones.
(sorry if i made some language mistakes, I'm french :P)
I'd like to say that it can be viable, but NOT optimal. A lot of people are responding like you MUST say no. Sorry to say, but I had someone play an adc Ashe support in Diamond 1 and it actually worked decent. The main ADC still takes all of the farm, and the Ashe basically harasses and does a build similar to ADC just with a lot less punch. It nets you an additional initiation tool/peeling tool. It allows for anyone trying to jump on the ADC to be essentially perma slowed.
So yes, there are benefits and it is viable BUT I would argue it's definitely situational. I wouldn't do it and expect your team to be happy with you though and be ready for rage. (still don't steal any additional CS from your main ADC.)
TL;DR; It has worked well for some people at Diamond 1. This is enough proof for me that there are situations and ways for it to work.