a/c issues

[snake109]

my heater core has been leaking prety bad so i bypassed it right where it comes out of the firewall. my car is running a little bit hotter but that was to be expected, the temp guage stays around the "O" and "R" area. but now when i have the a/c on, the compressor cuts off when it gets hot, but on a cold start it works untill it gets hot. even if i have the blower motor on high. is there a thermal switch that cuts off the compressor when the coolent gets a little too hot to help cool the radiator? what is the sensor in the coolant line right by the heater core in the engine bay for? thanks