When I engage the A/C it blows hot

Welcome to 2CarPros.

The system has pressure sensors. If there is no pressure, it will not allow the compressor to engage. That doesn't mean the compressor needs replaced. What really needs done is to have the system recharged to see two things. First, does the compressor engage and produce what is needed for it to cool the vehicle, and second, does the system maintain the pressure and not have a leak.

Here are a couple links you may find helpful:

https://www.2carpros.com/articles/car-air-conditioner-not-working-or-is-weak

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

If there is no pressure in the system, what I suggest is to vacuum the system and then recharge it. This is a good idea because while it is under a vacuum, you can determine if it holds vacuum. If it doesn't, then you know there is a leak and further diagnoses needs performed to locate the leak. It will save you money on Freon.

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

Here is a link that discusses leak detection:

https://www.2carpros.com/articles/air-conditioner-leak-detection

I hope something here helps. Let me know what you find and feel free to ask questions if you have them.

Take care,
Joe