I just refilled a bottle of auto air conditioning R-134a refrigerant for my car. Before refilling the pressure was read around 30 in blue safe zone. After refilled, the pressure meter reads normal at 35 (Normal range in blue zone) - LOW PRESSURE PORT. However, today when I was driving my car with my a/c on, I kind of feel like the compressor stop for few seconds, and then it switch on again. After I parked my car at home, I used the meter to measure the LOW PRESSURE PORT again, then it surprised me the pressure up to a much higher range in yellow zone (between 45-55), which is alert zone. Now, I turned my A/C OFF because I don't want to give extra work load to the compressor and the a/c system. Then I read my G's repair manual and found out that G has some kind of protection from either too high or too low pressure from refrigerant:

MY MANUAL SAID:
Refrigerant System Protection

REFRIGERANT PRESSURE SENSOR
The refrigerant system is protected against excessively high- or low-pressures by the refrigerant pressure sensor,
located on the condenser. If the system pressure rises above, or falls below the specifications, the refrigerant
pressure sensor detects the pressure inside the refrigerant line and sends the voltage signal to the ECM.
ECM makes the A/C relay go OFF and stops the compressor when pressure on the high-pressure side
detected by refrigerant pressure sensor is over about 2,746 kPa (28 kg/cm2 , 398 psi), or below about 134 kPa
(1.4 kg/cm2 , 20 psi).

PRESSURE RELIEF VALVE
The refrigerant system is also protected by a pressure relief valve, located in the rear head of the compressor.
When the pressure of refrigerant in the system increases to an unusual level [more than 3,727 kPa (38 kg/cm2
, 540 psi)], the release port on the pressure relief valve automatically opens and releases refrigerant into the
atmosphere. ***END***

My questions are:
(1) If the pressure relief valve can release the pressure automatically, do I have to worry the pressure is too high now?
(2) Or, can I release the refrigerant manually? If so, how to do it? I know repair shop use a machine to evacuate the refrigerant.

Thanks for your advice. : )

Tim

 

the valve is like your tire valve. you can push the center pin and the
gas will let out. use your refill can's nozzle (with the pressure gauge) and
push in alittle but not all the way. it will release the pressure...then
quickly lock it onto the valve to check the pressure. repeat as necessary.

im no pro at this, but ive had to refill my cooper-s number of times cause
it's got a small leak somewhere which my dealer failed to locate even after
4 attemps, new hoses, new compressor, etc.