There shouldn't be any liquid in the "intake" side of the system. This is largely prevented by the Thermal Expansion Valve (TXP), or on older vehicles, an orifice tube. These parts reside in, or just before, the evaporator - the heat exchanger internal to the vehicle in the HVAC housing under the dashboard.
At normal "at rest" temperatures and pressure, all the refrigerant will be in a gas phase. Exacly like Paulster opined.
Provided the system is not overfilled, the refrigerant will remain a dense gas until compressed and the temperature lowered - this pressure comes from the compressor, and the gas-to-liquid phase change will occur in the condenser (another heat exchanger, usually in front of the radiator).
If liquid were allowed to reach the intake side of the compressor, the unit would "hydrolock" and likely destroy the compressor if you weren't lucky enough to burn or break the belt first.
Answer to comment:
@Simone I'm not sure exactly what you are saying, but most gases have a fairly high boiling point compared to refrigerant. (R134a is about -15 degrees F). I'd rather call it "gas pressure" than vapor pressure, but in any case you can put thousands of psi of oxygen, helium, argon, and carbon dioxide in a tank, but none of it will be in liquid phase at normal "human" temperatures.
It all follows the Ideal Gas Law, PV=nRT, where pressure * volume is proportional to the moles (amount) * temperature * a constant (measurement units). The liquid phase (if any) is comparitively un-compressible (which is why it would break the compressor) and would not affect the pressure of a manifold gauge set reading. The gauges have no clue about temperature, only gas pressure. (There are fancy manifold sets with thermometers built in, but the gauges are still ignorant of temperature.) A chart is needed to determine if the observed pressures are appropriate for the specific refrigerant type and operating temperatures.
At rest, since I'm fairly certain all [R134a] refrigerant will be well above -15 degrees F, there should be no liquid anywhere in the system. As temperature increases, so will gas pressure. If pressure decreases suddenly, as with a small orifice discharging into the evaporator, a severe pressure drop must beget a severe temperature drop, since volume, moles, and the constant are not changing. Viola! Enjoy the "air conditioning"...