So my buddy owns a 2011 mustang 5.0 and this morning he went out and started it but the aftermarket head unit (Pioneer mixtrax) and ac controls were completely off. So I disconnected the negative terminal and reconnected it. Everything works but when he turns the ac on it works normal but then automatically turns down to barely any air coming out and after a few min goes back to normal then back down. Any idea what this could be? Let me know what y’all think thank you