---Not a Teacher---
In English, relative pronouns are who, whom, which, whose, and that.
A relative pronoun links two clauses into a single complex clause. It is similar in function to a subordinating conjunction. Unlike a conjunction, however, a relative pronoun stands in place of a noun. Compare:
(1) This is a house. Jankie built this house.
(2) This is the house that Jankie built.
Sentence (2) consists of two clauses, a main clause (This is the house) and a relative clause (that Jack built). The word that is a relative pronoun. Within the relative clause, the relative pronoun stands for the noun phrase it references in the main clause (its antecedent), which is one of the arguments of the verb in the relative clause. In the example, the argument is the house, the direct object of built. Note the word "that" appears twice in the prior sentence, but the first is a demonstrative pronoun.
Other arguments can be relativised using relative pronouns:
Subject: Hunter is the boy who kissed Monique.
Indirect object: Hunter is the boy to whom Monique gave a gift.
Adpositional complement: Jack built the house in which I now live. (and similarly with prepositions and prepositional phrases in general, eg These are the walls in between which Jack ran.)
Possessor: Jack is the boy whose friend built my house.
Conclusion: "as" acts as a conjunction in my opinion.
Looking forward to see more answers to it.