my coolant leaks out fast when the engine heats up only on freezing weather?

Strange. Pressure check passed and you lose coolant when you use heat.... givin the year of your vehicle I would bet your hoses to, or your heater core are bad. Do your windows steam up? Does your passenger floor get wet or front center under the dash get wet?

Your Prizm has a heater control valve. Basically what the valve does is turn the coolant flow on or off to the heater core depending on the temperature setting on the dash control panel. There's a cable that goes from the control panel on the dash to the heater control valve. When warmer air is selected the valve opens to allow coolant to flow through the heater core. When cooler air is selected the valve is closed so no coolant flows through the heater core. I would suspect that valve or the heater core is leaking. Hope that helps! Jim