A/C blows hot air when engine is idling

Hello,

Typically if you have low Freon and or clogged condenser.
You should first check the Freon level. If it is low it needs to be recharged.

Here is couple of helpful article of how to recharge your A/C system:

https://www.2carpros.com/articles/air-conditioner-how-to-add-freon
https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

https://youtu.be/uZrQCGwXfek

If the Freon level is correct then second item could be a clogged or damaged condenser.
If the condenser is faulty then you won't have proper amount of air flowing through it to make the air cold out of the vent.

Please let me know if you have any questions.

Thank you.