You may have one of two problems,1) Your A/C system is low on 134a Freon charge. or 2) the connecting high pressure switch is not making good contact. I would check nu. 2 first because if the compressor is not coming on at all it's going to blow hot air but the A/C indicator light will still be on. If it's low on charge, the light will blink off and on.

In the above case, AC is likely to give out air at the same temperature without any cooling or heating.

However if the AC starts giving hot air into your room in cooling mode than the problem could be in the radiator cooling. Reason could be choking of the radiator cooling coils which blow hot air out from the back of your AC. This generally happens if the external part of your room AC is situated around potential choking materials lying loose such as waste, birds feathers etc. The radiator fan sucks such loose material into the radiator coils which get choked, resulting in back-flow of hot air of the radiator into your room. It also adversely affects the cooling cycle as the gas does not get cooled adequately, in the radiator.

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