i have no peddle pressure and i already replaced the master cylinder
Low pressure valve.
A pressure switch a valve that shuts off the unit when the pressure is to low or to high
Near the metering unit.
If the guage is registering full all or when under half a tank it is a faulty sending unit. Cost is in the hu8ndred to repair.
It does NOT automatically mean you have 80# of pressure! NEVER trust your gauges as being the 'last word'. They're notoriously cranky on some older XJ's. (Usually due to gauge cluster connection issues or harness oxidation.) Chances are that you have a defective oil pressure sending unit. Rarely the gauge goes bad. Remove the wire on the sending unit and see if that changes the reading. If it does, replace the sending unit. If not, I'd still replace the sending unit. After you confirm the oil pressure sending unit is good, check the oil pressure relief valve. It may be stuck closed resulting in high pressure reading.
It does NOT automatically mean you have 80# of pressure! NEVER trust your gauges as being the 'last word'. They're notoriously cranky on some older XJ's. (Usually due to gauge cluster connection issues or harness oxidation.) Chances are that you have a defective oil pressure sending unit. Rarely the gauge goes bad. Remove the wire on the sending unit and see if that changes the reading. If it does, replace the sending unit. If not, I'd still replace the sending unit. After you confirm the oil pressure sending unit is good, check the oil pressure relief valve. It may be stuck closed resulting in high pressure reading.
The high pressure (discharge) side starts at the compressor outlet and ends at the metering device inlet. This side will have the smaller refrigerant lines. The low pressure (vacuum) side begins at the metering device outlet and ends at the compressor inlet. This side will have the larger refrigerant lines.
replace oil sensor unit
The fuel pump has a check valve that holds the fuel pressure. The sending unit monitors the fuel level in the fuel tank.
Simple answer NO.
Metering device The metering device controls the flow of liquid refrigerant through the system. The liquid enters at a high-pressure, high-temperature, sub-cooled state and leaves as a low-pressure, low temperature, expanded liquid state. Accurator Piston and Thermostatic Expansion Valves are the most widely used metering devices. Accurator Pistons are widely used because of their low cost and flexibility. The piston can easily be changed to match the capacity of the condensing unit. The Thermostatic Expansion Valve (TXV) is the most efficient type of metering device. The TXV automatically adjusts the flow of the liquid refrigerant based on the superheat of the refrigerant leaving the evaporator coil. As the load on the evaporator increases, the TXV increases the flow of refrigerant. This maintains the proper superheat. The TXV is efficient throughout a variety of system operating conditions, while the accurator is efficient only under designed conditions.
To add refrigerant to an AC unit, you need to first locate the service valve on the unit. Then, connect a refrigerant charging hose to the valve. Next, slowly add the refrigerant into the system while monitoring the pressure levels. Be careful not to overfill the unit. Finally, close the valve and check the AC unit to ensure it is working properly.